DENTAL  DEPARTMENT 


A  TREATISE 


ON 


HUMAN  PHYSIOLOGY; 


DESIGNED   FOB   THE   USE   OF 


STUDENTS  AND  PRACTITIONERS  OF  MEDICINE. 


BY 

JOHN   C.  DALTON,  M.D., 

PROFESSOR  OF  PHYSIOLOGY  AND  HYGIENE  IN  THE  COLLEGE  OF  PHYSICIANS  AND  SURGEONS, 

NEW  YORK  ;  MEMBER  OF  THE  NEW  YORK  ACADEMY  OF  MEDICINE  ;  OF  THE  NEW  YORK 

PATHOLOGICAL  SOCIETY  ;  OF  THE  AMERICAN  ACADEMY  OF  ARTS  AND  SCIENCES, 

BOSTON;    OF  THE   BIOLOGICAL   DEPARTMENT  OF  THE  ACADEMY  OF 

NATURAL  SCIENCES,  PHILADELPHIA;  AND  OF  THE  NATIONAL 

ACADEMY  OF  SCIENCES  OF  THE  UNITED  STATES  OF  AMERICA. 


SEVENTH  EDITION, 

WITH 


awl    tft- 


PHILADELPHIA: 

HENRY  C.  LEA'S  SON  &  CO. 

1882. 


Entered,  according  to  the  Act  of  Congress,  in  the  year  1882,  by 

HENRY  C.  LEA'S  SON  &  CO., 
In  the  Office  of  the  Librarian  of  Congress.    All  rights  reserved. 


3)15 


TO  MY  FATHEE, 


JOHN  0.  DAL  TON,  M.D., 


IN 


HOMAGE    OF    HIS    LONG    AND    SUCCESSFUL    DEVOTION" 


TOTHE 


SCIENCE  AND  AET  OF  MEDICINE, 


GRATEFUL  RECOLLECTION  OF  HIS  PROFESSIONAL  PRECEPTS  AND  EXAMPLE, 


IS    RESPECTFULLY  AND  AFFECTIONATELY 


INSCRIBED. 


PREFACE. 


OINCE  the  last  edition  of  this  work,  nearly  all  the  departments  of 
medicine  have  been  cultivated  with  marked  success ;  and  the  ad- 
vances in  physiological  science  during  that  time  have  made  it  desirable 
to  revise  the  greater  part  of  the  book,  and,  in  some  respects,  to  modify 
its  arrangement.  In  the  section  of  Physiological  Chemistry,  the  most 
important  alterations  relate  to  the  classification  of  the  Albumenoid 
Substances,  and  particularly  to  the  prominence  given  to  the  Ferments 
as  a  special  group.  Although  we  are  still  very  imperfectly  acquainted 
with  the  chemical  constitution  of  these  bodies,  and  are  even  able  to 
recognize  them  rather  by  the  effects  which  they  produce  than  by  their 
physical  properties,  yet  their  physiological  activity  has  assumed  an  im- 
portance which  makes  it  necessary  to  consider  them  by  themselves.  In 
treatises  exclusively  devoted  to  Physiological  Chemistry,  the  albumenoid 
substances  are  usually  classified  according  to  their  characters  of  solu- 
bility in  neutral,  acid,  or  alkaline  media,  or  in  saline  solutions  of  dif- 
ferent degrees  of  concentration,  or  by  the  varying  conditions  of  their 
coagulability  ;  but  in  a  work  like  the  present,  an  arrangement  based  on 
their  physiological  properties  and  destination  is  both  more  useful  and 
more  intelligible.  The  same  remark  will  apply,  in  great  measure,  to 
the  other  principal  groups  of  organic  substances. 

In  the  department  of  the  Nervous  System,  more  extended  considera- 
tion has  been  given  to  the  localization  of  function  in  special  parts  of  the 
cerebro-spinal  axis.  The  recent  progress  of  investigation  in  this  respect 
relates  not  only  to  the  cerebral  convolutions  and  their  connection  with 
various  forms  of  movement  and  sensation,  but  also  to  the  identification 
of  special  communicating  tracts  of  white  substance  in  the  brain  and 
spinal  cord.  The  general  use  of  hardened  and  stained  preparations,  and 
improved  methods  in  making  microscopic  sections,  have  largely  increased 
our  knowledge  of  the  intimate  structure  of  the  nervous  centres;  and 

v 


VI  PREFACE. 

the  study  of  nervous  degenerations  has  proved  an  additional  source  of 
information  in  regard  to  their  deep-seated  connections.  Although  the 
anatomical  data  obtained  in  this  way  must  be  insufficient  by  themselves 
to  determine  the  functions  of  a  part,  yet  they  are  of  material  aid  in 
the  contrivance  and  execution  of  physiological  experiments,  and  often 
indispensable  for  the  explanation  of  their  results.  Furthermore,  the 
study  of  the  vaso-motor  nerves  and  nerve  centres  has  reached  a  devel- 
opment which  makes  it  almost  a  special  department  of  nervous  physi- 
ology, and  requires  a  more  extended  treatment  than  heretofore. 

The  method  of  examination  by  microscopic  sections  has  also  been 
found  of  advantage  in  Embryology.  It  shows  the  form  and  position 
of  the  organs'  at  their  earliest  period  of  development,  and  enables  the 
observer  to  trace  their  subsequent  changes  with  greater  precision  than 
formerly.  The  most  primitive  embryonic  structures  are  still  those  which 
present  the  greatest  difficulty  in  their  study  and  interpretation;  but 
increased  facilities  of  research  are  constantly  adding  to  our  knowledge 
in  this  respect,  and  reducing  the  number  of  doubtful  or  disputed  points. 
In  the  present  work,  as  a  general  rule,  topics  which  are  uncertain  or 
incomplete  have  been  treated  with  comparative  brevity,  a  greater  space 
being  devoted  to  those  wrhich  are  demonstrated  by  satisfactory  evidence. 
The  number  of  wood-cuts  has  been  somewhat  reduced,  and  many  have 
been  replaced  by  new  ones,  intended  either  for  the  illustration  of  recent 
discoveries  or  as  improvements  on  those  of  the  former  edition. 

NEW  YORK,  December,  1881. 


CONTENTS. 


INTRODUCTION. 

PAGE 

Definition  of  Physiology — Method  of  Study  by  Observation — Organization 
of  the  Body — Physiological  Properties  of  Separate  Parts — Their  Func- 
tional Activity  during  Life — Observation  and  Experiment  on  the  Living 
Body — Present  Features  of  Physiological  Study — General  Phenomena  of 
Living  Creatures — Special  Phenomena — Departments  of  Physiology  25-29 

SECTION  I. 
PHYSIOLOGICAL    CHEMISTRY. 

CHAPTER  I. 

CHEMICAL    INGREDIENTS    OF    THE    BODY. 

Composite  Nature  of  the  Animal  Fluids  and  Tissues — Variety  of  the  Ingre- 
dients— Mode  of  Extraction — Their  Proportions  and  Physiological  Vari- 
ations—Their Classification 30-34 

CHAPTER  II. 

INORGANIC    SUBSTANCES. 

Nature  and  Importance  of  the  Inorganic  Ingredients  of  the  Body — Their 
Enumeration — Water — Lime  Phosphate — Lime  Carbonate — Magnesium 
Phosphate — Sodium  Chloride — Potassium  Chloride — Sodium  and  Potas- 
sium Phosphates — Sodium  and  Potassium  Carbonates  —  Sodium  and 
Potassium  Sulphates— Source,  Usefulness,  and  Final  Discharge  of  the 
Inorganic  Ingredients  of  the  Body 35-48 

CHAPTER  III. 

HTDROCARBONACEOUS  SUBSTANCES. 

Origin,  Composition,  and  General  Characters  of  the'Hydrocarbonaceous 
Substances — Carbo-Hydrates— Starch— Its  Production  in  Vegetables- 
Its  Proportion  in  Different  Kinds  of  Food— Its  Physical  Properties  and 
Reactions — Transformation  into  Dextrine  and  Sugar — Its  Digestion — Its 
Changes  in  Vegetation — Sugar — General  Characters  of  the  Saccharine 

vii 


Vlll  CONTENTS. 

PAGE 

Group — Varieties — Glucose — Its  Source  and  Production — Reactions — 
Fermentation — Lactose — Saccharose — Glycogen — Fats — Their  Origin  in 
Vegetation  — Varieties  —  Stearine  —  Palmitine — Oleine  — Their  Physical 
Properties  and  Reactions — Emulsification — Saponification — Their  Con- 
dition in  the  Living  Body — Physiological  Relations  of  Fat  — Choles- 
terine 49-72 

CHAPTER  IV. 

ALBUMENOID    SUBSTANCES. 

General  Characters  of  the  Alhumenoid  Suhstances — Composition — Solu- 
bility— Coagulation — Catalytic  Action — Putrefaction — Origin  in  Vegeta- 
tion— Classification — ALBUMINOUS  MATTERS — Albumen — Caseine — Para- 
globuline  —  Fibrinogen  —  Myosine — Sy  ntonine  —  Peptone — FERMENTS — 
Ptyaline — Pepsine — Pancreatine — Trypsine — Fibrine-Ferment — Diastase 
— MUCIFORM,  GELATINOUS,  AND  SOLID  ALBUMENOID  SUBSTANCES — Mucine — 
Gelatine — Chondrine — Elastine — Keratine — Source,  Changes,  and  Des- 
tination of  Albumenoid  Substances 73-91 

CHAPTER  V. 

COLORING   MATTERS. 

Composition  and  General  Characters  of  the  Coloring  Matters  —  ITemo- 
globine — Its  Crystallization — Color — Spectrum — Its  Functional  Activity 
and  Changes  in  the  Body — Melanine — Composition — Reactions — Deri- 
vation— Bilirubine  —  Bili  verdine — Reactions  —  Spectrum — Derivation— 
Urochrome — Chlorophylle 92-104 

CHAPTER  YI. 

CRYSTALLIZABLE   NITROGENOUS   MATTERS. 

General  Characters  of  the  Group — Lecithine — Cerebrine — Leucine — Tyro- 
sine — Sodium  Glycocholate — Sodium  Taurocholate — Mutual  Relations 
of  the  Biliary  Salts— Pettenk  of  er's  Test — Its  Spectrum — Creatine — Cre- 
atinine— Urea — Source  of  Urea— Its  Daily  Quantity  and  Variations- 
Relation  to  Food  and  Exercise — Sodium  Urate — Uric  Acid — Sodium 
Hippurate— Hippuric  Acid 105-118 

CHAPTER  VII. 

FOOD. 

Inorganic  Ingredients  of  the  Food— Non-Nitrogenous  Organic  Ingredients 
— Carbo-Hydrates— Fats— Their  Insufficiency  for  Nutrition— Nitrogenous 
Ingredients — Their  Importance— Their  Insufficiency— Composition  of 
Different  Articles  of  Food— Milk  — Cheese  — Butter  — Bread  — Meat — 
Eggs— Vegi'tnhU-s  —  Requisite  Quantity  of  Food  and  of  its  DittVivnt  In- 
gredients— Proportion  of  Albuminous  and  Non-Nitrogenous  Substances 
— Diet-Tables  under  Different  Conditions — Chemical  Elements  in  the 
Food— Interim!  Consumption  and  Excretory  Products  of  the  Food  119-135 


CONTENTS.  IX 


SECTION  II. 
FUNCTIONS    OF 

CHAPTER  I. 

DIGESTION. 

PAGE 

Organs  of  Digestion—  Alimentary  Canal  —  Digestive  Fluids  —  Their  Action 
on  the  Food  —  Mastication  —  SALIVA—  Salivary  Glands  —  Physical  Prop- 
erties and  Composition  of  the  Saliva  —  Its  Mode  of  Secretion  —  Daily 
Quantity  —  Its  Physiological  Action  —  GASTEIC  JUICE  —  Gastric  Follicles  — 
Gastric  Fistula  —  Physical  Properties  and  Composition  of  the  Gastric 
Juice  —  Its  Free  Acid  —  Pepsine  —  Pepsine  Extracts  and  Artificial  Digestive 
Fluids  —  Physiological  Action  of  Gastric  Juice  —  Syntonine  —  Peptone  — 
Self-Digestion  of  the  Stomach  —  Daily  Quantity  of  Gastric  Juice  —  Pro- 
cess of  Stomach  Digestion  —  Digestion  of  Bread,  Cheese,  Adipose  Tissue, 
Muscular  Flesh,  Milk,  and  Vegetable  Tissues  —  Reabsorption  of  the  Gas- 
tric Juice  —  PANCEEATIC  JUICE  —  Its  Physical  Properties  and  Composition 

—  Pancreatine  —  Trypsine—  Acidification  of  Fats  —  Mode  of  Secretion  and 
Daily  Quantity  of  the  Pancreatic  Juice  —  Its  Physiological  Action  —  THE 
BILE  —  Its  Physical  Properties  and  Composition  —  Mode  of  its  Secretion 
and  Discharge  —  Daily  Quantity  —  Physiological  Action  —  INTESTINAL 
JDICE  —  its  Physical  Properties  and  Composition  —  Its  Physiological  Action 

—  Intestinal  Digestion  —  The  Large  Intestine  and  its  Contents         .     136-194 

CHAPTER   II. 

ABSORPTION. 

Villi  of  the  Intestine—  Closed  Follicles  of  the  Intestine—  Absorption  by 
the  Villi  —  Chyle  —  Absorption  by  the  Blood-Vessels  —  Absorption  by  the 
Lacteals  —  Lacteals  and  Lymphatics  —  Passage  of  Absorbed  Materials  into 
the  Circulation  —  Absorption  of  Carbo-Hydrates  and  Production  of  Gly- 
cogen  in  the  Liver  —  Transformation  of  the  Glycogen  into  Glucose  — 
Absorption  and  Disappearance  of  the  Liver-Sugar  —  Accumulation  of 
Glucose  in  the  Blood  and  its  Discharge  by  the  Urine  .  .  .  195-211 

CHAPTER  III. 

THE    BLOOD. 

Physical  Properties  and  Constitution  of  the  Blood  —  RED  GLOBULES—  Their 
Physical  Properties  —  Their  Composition  —  Their  Varieties  in  Different 
Animals  —  Diagnosis  of  Blood  and  Blood-Stains  —  Physiological  Function 
of  the  Red  Globules  —  WHITE  GLOBULES  of  the  Blood  —  Their  Amoeboid 
Movements  —  Their  Physiological  Functions  —  PLASMA  of  the  Blood  —  Its 
Composition  —  Albumen  —  Paraglobuline  —  Fibrinogen  —  Peptone  —  Fatty 
Matters  —  Mineral  Salts  —  Coagulation  of  the  Blood  —  Clot  and  Serum  — 
Conditions  of  Coagulation  —  Nature  of  Coagulation—  Usefulness  of  Coag- 
ulation—Quantity of  Blood  in  the  Body  .....  212-231 


X  CONTENTS. 

CHAPTER  IV. 

RESPIRATION. 

PAGE 

Nature  of  Respiration — In  Animals  and  Vegetables — Organs  of  Respira- 
tion—  Gills  —  Lungs  —  Movements  of  Respiration — Their  Frequency — 
Quantity  of  Air  Used  in  Respiration— Changes  in  the  Air  by  Respiration 
— Absorption  of  Oxygen — Exhalation  of  Carbonic  Acid — Exhalation  of 
AVatery  Vapor— Of  Organic  Matter — Vitiation  of  the  Air  by  Respiration 
— Relations  between  the  Oxygen  Absorbed  and  the  Carbonic  Acid  Given 
Off — Changes  in  the  Blood  by  Respiration — Color  of  Arterial  ami  Venous 
Blood — Exchange  of  Gases  in  the  Blood — Destination  of  the  Oxygen — 
Source  of  the  Carbonic  Acid — Respiration  by  the  Tissues  .  .  232-257 

CHAPTER  V. 

ANIMAL   HEAT. 

Temperature  of  the  Animal  Body — In  Different  Classes — Internal  Produc- 
tion of  Heat — Quantity  of  Heat  Produced  in  the  Body — Normal  Varia- 
tions of  Temperature  in  the  Body — Mode  of  Production  of  Animal  Heat 
— Relations  of  Heat-Production  and  Respiration — Local  Heat-Production 
in  the  Organs  and  Tissues — Cooling  Action  of  the  Lungs  and  Skin — 
Regulation  of  the  Animal  Temperature — Effects  of  Lowering  the  Bodily 
Temperature — Effects  of  Elevating  the  Bodily  Temperature — Resistance 
of  the  Body  to  External  Cold  —  Resistance  of  the  Body  to  External 
Heat 258-273 

CHAPTER   VI. 

THE    CIRCULATION. 

The  Circulatory  Apparatus — The  Heart — Cardiac  Sounds,  Movements,  and 
Impulse — Rhythm  of  the  Heart's  Action — Pressure  of  Blood  in  the 
Heart's  Cavities — The  Arterial  Circulation — Movement  of  Blood  through 
the  Arteries — Arterial  Pulse — Equalization  of  the  Arterial  Blood  Current 
— Arterial  Pressure — Rapidity  of  the  Arterial  Current— The  Venous 
Circulation — Movement  of  Blood  through  the  Veins — Rapidity  of  the 
Venous  Current — The  Capillary  Circulation — Capillary  Blood- Vessels — 
Movement  of  Blood  in  the  Capillary  Vessels — Physical  Cause  of  the 
Capillary  Circulation — Velocity  of  Blood  in  the  Capillaries — General 
Rapidity  of  the  Circulation — Local  Variations  in  the  Capillary  Circula- 
tion    274-306 

CHAPTER   VII. 

THE    LYMPHATIC    SYSTEM. 

General  Structure  and  Arrangement  of  the  Lymphatic  System — Origin  and 
Course  of  tin-  Lymphatic  Vessels — The  Lymphatic  Glands — Transudation 
and  Absorption  by  Animal  Tissues — EndosiiK»is  and  Kxosmosis— Phys- 
ical Conditions  Influencing  Kndosmosis— Nature  of  the  Process  Absorp- 
tion and  Transudation  in  the  Living  Body — Lymph  ami  Chyle — Move- 


CONTENTS.  XI 

PAGE 

merit  of  Lymph  in  the  Lymphatic  Vessels — Daily  Quantity  of  Lymph 
and  Chyle — Internal  Renovation  of  the  Animal  Fluids  .         .         .     307-323 

CHAPTER  VIII. 

THE    URINE. 

Excretion  in  General — Excrementitious  Substances — Distinctive  Character 
of  the  Urine — Its  Physical  Properties — Its  Variations  in  Quantity,  Acid- 
ity, and  Specific  Gravity — Ingredients  of  the  Urine — Urea — Creatinine 
— Urates — Alkaline  Phosphates — Earthy  Phosphates— Chlorides — Sul- 
phates— Reactions  of  the  Urine  to  Heat — To  Acids — To  Alkalies— To 
Mineral  Salts — Abnormal  Ingredients  of  the  Urine — Glucose — Biliary 
Matters  —  Medicinal  and  Poisonous  Substances  —  Albumen  —  LTrinary 
Deposits — Earthy  Phosphates — Urates — Uric  Acid  —  Blood  —  Mucus  — 
Pus  —  Decomposition  of  the  Urine  —  Acid  Fermentation — Deposit  of 
Oxalic  Acid — Alkaline  Fermentation — Formation  of  Ammonium  Car- 
bonate— Arnmonio-Magnesium  Phosphate — Final  Disappearance  of  the 
Urea  324-341 


SECTION  III. 

THE   NEKYOUS    SYSTEM. 
CHAPTER  I. 

GENERAL  STRUCTURE  AND  FUNCTIONS  OF  THE    NERVOUS  SYSTEM. 

Mode  of  Action  of  the  Nervous  System  in  General — Its  Anatomical  Ele- 
ments— White  and  Gray  Substance — Nerve  Fibres — Their  Constituent 
Parts — Medullated  and  Non-medullated  Nerve  Fibres — Course  and  Mu- 
tual Relation  of  Nerve  Fibres — Their  Peripheral  Termination — Their 
Physiological  Properties — Motor  and  Sensitive  Nerve  Fibres — Degener- 
ation and  Regeneration  of  Divided  Nerves — Nerve  Cells — Their  Form 
and  Structure — Connection  between  Nerve  Fibres  and  Nerve  Cells — 
Physiological  Properties  of  Nerve  Cells — Nervous  Centres — Reflex  Ac- 
tion of  the  Nervous  System 342-360 

CHAPTER  II. 

NERVOUS   IRRITABILITY    AND    ITS    MODE   OF    ACTION. 

Irritability  in  General — Irritability  of  Sensitive  Fibres — Of  Motor  Fibres — 
Identity  of  Action  in  Motor  and  Sensitive  Fibres— Rapidity  of  Trans- 
mission of  the  Nerve  Force — Experiments  on  Separated  Frog's  Legs — 
On  the  Living  Human  Body — Rate  of  Transmission  in  the  Motor  Nerves 
— In  the  Sensitive  Nerves — In  the  Spinal  Cord — Rapidity  of  Nervous 
Action  in  the  Brain — Personal  Error  and  Personal  Equation  .  .  361-372 


Xll  CONTENTS. 

CHAPTER  in. 

GENERAL   ARRANGEMENT   OF   THE   NERVOUS   SYSTEM. 

PAGE 

Secondary  Groups  of  Nerves  and  Nervous  Centres — The  Cerebro-Spinal 
System — Its  Nervous  Centres — Commissures — Decussations — The  Spinal 
Cord — Its  Gray  Substance — Anterior  and  Posterior  Horns — Origin  of 
Nerve  Roots— White  Substance  of  the  Cord— Anterior,  Middle,  and 
Posterior  Columns— The  Brain— In  Fish  and  Reptiles— In  Birds— In 
Quadrupeds — The  Cerebral  Ganglia — In  Man — Connections  of  the  Brain 
with  Spinal  Cord — Medulla  Oblongata — Tuber  Annulare — Crura  Cerebri — 
Internal  Capsule — Corona  'Radiata — Convolutions  of  the  Cortex — Pass- 
age of  Nervous  Impulses  between  the  Brain  and  Peripheral  Parts  .  373-380 

CHAPTER   IV. 

THE    SPINAL    CORD. 

General  Configuration  and  Function  of  the  Spinal  Cord — Arrangement  of 
its  Gray  and  WJiite  Substance — Connections  of  the  Spinal  Nerve  Roots — 
Connection  of  Spinal  Cord  with  the  Brain — Decussation  of  the  Pyra- 
mids— Continuations  of  the  Crura  Cerebri — Transmission  of  Motor  and 
Sensitive  Impulses  in  the  Spinal  Cord  and  Nerves — Centripetal  and  Cen- 
trifugal Degeneration  of  Divided  Nerve  Fibres— Sensitive  and  Excitable 
Parts  of  the  Spinal  Cord  and  Nerve  Roots — Channels  for  Sensation  and 
Movement  in  the  Spinal  Cord — Crossed  Action  of  the  Spinal  Cord — The 
Spinal  Cord  as  a  Nervous  Centre — Reflex  Action — Physiological  Action 
of  the  Cord  as  a  Nervous  Centre 381-412 

CHAPTER  V. 

THE    BRAIN. 

General  Divisions  of  the  Brain — THE  HEMISPHERES — Fissures  and  Convolu- 
tions— Cerebral  Ganglia — Internal  Capsule — External  Capsule — Gray 
Substance  of  the  Convolutions— Its  Structure  in  Special  Parts  of  the 
Hemispheres — Course  of  Fibres  in  the  White  Substance  of  the  Hemi- 
spheres— Commissural  Fibres — Fibres  of  Association — Medullary  Fibres 
— Physiological  Properties  and  Function  of  the  Hemispheres — Localiza- 
tion of  Function  in  Different  Parts  of  the  Hemispheres — Centres  of 
Motion — Centres  of  Sensation— Centre  of  Language — Ilemiplegia  and 
Ikiniana'sthesia  from  Cerebral  Lesions — THE  CEREBELLUM — Its  Struc- 
ture and  Connections — Its  Physiological  Properties — Loss  of  Muscular 
Coordination  from  Injury  of  the  Cerebellum — THE  MEDULLA  OBLONGATA 
— Arrangement  of  its  Gray  Substance — Its  Physiological  Properties — Its 
Connection  with  Respiration — With  Deglutition — With  Plionation — With 
Articulation 413-145 

CHAPTER   VI. 

THE   CRANIAL    NERVES. 

General  Characters  and  Classiticntion  of  the  Cranial  Nerves— THE  OLFAC- 
TORY NERVES — Their  Physiological  Properties— OPTIC  NERVES — Their 


CONTENTS.  Xlll 

PAGE 

Physiological  Properties — Their  Decussation — OCULOMOTORIUS — Its  De- 
cussation — Its  Physiological  Properties — PATIIETICUS— Its  Physiological 
Properties — TRIGEMINUS — Its  Physiological  Properties — Painful  Affec- 
tions of  the  Trigeminus— Its  Lingual  Branch— Muscular  Branches — 
Anastomotic  Branches — Its  Influence  on  the  Special  Senses — ABDUCENS 
— Its  Physiological  Properties — FACIAL — Its  Physiological  Properties — 
Facial  Paralysis — Crossed  Action  of  the  Facial  Nerve — Its  Sensibility — 
Its  Communications  in  the  Aqueduct  of  Fallopius — Chorda  Tympani — 
THE  AUDITORY  NERVE — Its  Physiological  Properties — GLOSSOPHARYN- 
GEAL — Its  Physiological  Properties — Its  Connection  with  the  Sense  of 
Taste — "With  Deglutition — PNEUMOGASTRIC—  Its  Physiological  Proper- 
ties— Its  Connection  with  Eespiration— With  the  Voice — With  Degluti- 
tion— With  Stomach  Digestion — Its  Influence  on  the  Heart — SPINAL 
ACCESSORY — Its  Motor  Properties — Its  Connection  with  the  Voice — With 
Muscular  Effort — HYPOGLOSSAL — Its  Physiological  Properties — Its  Con- 
nection with  Mastication  and  Deglutition — With  Articulation  .  446-495 

CHAPTER  VII. 

THE    SYMPATHETIC    SYSTEM. 

General  Arrangement  of  the  Sympathetic  System — The  Sympathetic  Gan- 
glia—Sensibility and  Motor  Power  of  the  Sympathetic  System— Its  Con- 
nection with  the  Special  Senses — Vaso-motor  Nerves  and  Nerve  Centres 
— Muscularity  and  Contractility  of  the  Blood- Vessels — Rhythmical  Con- 
traction of  Arteries  in  Particular  Regions— Contraction  and  Dilatation  of 
Arteries  under  Nervous  Influence — Centres  of  Origin  of  the  Vaso-motor 
Nerves — Tonic  Contraction  of  Blood- Vessels — Its  Influence  on  the  Local 
Circulation — Dilator  Nerves — Action  of  Arrest — Reflex  Contraction  and 
Dilatation  of  the  Blood- Vessels 496-509 

CHAPTER  VIII. 

THE    SENSES. 

General  Sensibility — SENSE  OF  TOUCH — Its  Acuteness  and  Delicacy  in  Dif- 
ferent Regions — Sensations  of  Temperature — Sensations  of  Pain — Mode 
of  Action  of  the  Senses  in  General — SENSE  OF  TASTE — Necessary  Con- 
ditions of  its  Exercise — Persistence  of  Gustatory  Impressions — SENSE 
OF  SMELL — Conditions  of  its  Exercise — Its  Acuteness  in  Man  and  Ani- 
mals— SENSE  OF  SIGHT — Organ  of  Vision — Its  Envelopes  and  Refractive 
Media — Crystalline  Lens — Retina — Blind  Spot — Macula  Lutea  and  Fovea 
—Acuteness  of  Sensibility  of  the  Retina— The  Retinal  Red  and  its  Alter- 
ation by  Light — Physiological  Conditions  of  the  Sense  of  Sight — Field 
of  Vision — Line  of  Direct  Vision — Point  of  Distinct  Vision — Accommo- 
dation— Presbyopia — Myopia — Binocular  Vision — Appreciation  of  Solid- 
ity and  Projection — General  Laws  of  Visual  Perception — Persistence  of 
Visual  Impressions — Negative  Images — SENSE  OF  HEARING — External 
Ear— Tympanum  and  Chain  of  Bones — Labyrinth — Physiological  Action 
of  the  Membranous  Labyrinth — Office  of  the  Semi-Circular  Canals — 
Cochlea— Organ  of  Corti— Physiological  Action  of  the  Cochlea— Per- 
sistence of  Sonorous  Impressions — Production  and  Perception  of  Musical 
Sounds  510-568 


XIV  CONTEXTS. 

SECTION  IV. 

REPRODUCTION. 

CHAPTER  I. 

NATURE    OF    REPRODUCTION,    AND    THE    ORIGIN    OF    PLANTS    AND 

ANIMALS. 

PAGE 

Phases  of  Existence  in  Plants  and  Animals — Their  Reproduction — Repro- 
duction by  Generation — Resemblance  of  Progeny  to  Parents— Sponta- 
neous Generation — Sources  of  Error — Reproduction  of  Entozoa — Of  Cvs- 
ticercus  Cellulosao — Of  Trichina  Spiralis — Of  Infusoria — Of  Bacteria — 
Conclusion  in  Regard  to  Spontaneous  Generation — Sexual  Generation  509-583 

CHAPTER  II. 

THE  EGG  AND  FEMALE  ORGANS  OF  GENERATION. 

Constituent  Parts  of  the  Egg — Vitelline  Membrane — Vitellus — Germina- 
tive  Vesicle — Germinative  Spot — Ovaries  and  Oviducts — Action  of  the 
Oviducts  and  other  Generative  Passages — Formation  of  the  Fowl's  Egg 
— Female  Generative  Organs  in  Quadrupeds  and  Man — Fallopian  Tubes 
—Uterus 584-591 

CHAPTER  III. 

THE    SPERMATIC   FLUID   AND   MALE   ORGANS   OF   GENERATION. 

The  Spermatozoa — Their  Anatomical  Characters — Their  Movement — Their 
Formation — Accessory  Male  Organs  of  Generation — Conditions  of  Fecun- 
dation by  the  Spermatic  Fluid — Penetration  of  Spermatozoa  into  the 
Egg — Their  Union  with  the  Vitellus — Sexual  Congress — Fecundation  of 
the  Egg  in  the  Generative  Passages 592-598 

CHAPTER  IV. 

OVULATION  AND  MENSTRUATION. 

Ovulation — Original  Formation  of  Eggs  in  the  Ovaries — Their  Periodical 
Development  and  Discharge — Rupture  of  the  Graafian  Follicle — Escape 
of  the  Egg — Accompanying  Phenomena — Menstruation — Phenomena  of 
the  Menstrual  Period — Ovulation  in  Menstruation — Relations  of  the 
Menstrual  Flow  to  the  Discharge  of  the  Egg — Passage  of  the  Egg  through 
the  Fallopian  Tube — Abnormal  Location  of  the  Impregnated  Kgg — Ova- 
rian, Abdominal,  and  Tubal  Pregnancies— Source  of  the  Menstrual  Hem- 
orrhage    599-607 

CHAPTER  V. 

THE    CORPUS    LUTEUM,    AND    ITS    CONNECTION    WITH    MENSTRU- 
ATION  AND    PREGNANCY. 

Obliteration  of  the  Ruptured  (Iraatian  Follicle — Its  Conversion  into  a  Cor- 
pus Luteum — CORPUS  LUTEUM  OF  MENSTRUATION — Rupture  of  the  Graa- 


CONTENTS.  XV 

PAGE 

fian  Follicle — Formation  of  the  Clot — Hypertrophy  of  the  Vesicular 
Membrane — Its  Yellow  Color — Decolorization  and  Condensation  of  the 
Clot — Atrophy  and  Disappearance  of  the  Corpus  Luteum — Weight  of 
the  Corpus  Luteum  at  Different  Periods  after  Menstruation — CORPUS 
LUTEUM  OF  PKEGNANCY— Its  Early  Condition— Its  Growth  and  Develop- 
ment during  Pregnancy — Its  Condition  at  Term — Its  Atrophy  after 
Delivery — Distinctive  Characters  of  the  Corpus  Luteum  in  Menstruation 
and  Pregnancy G08-615 

CHAPTER  VI. 

DEVELOPMENT  OF  THE  IMPREGNATED  EGG SEGMENTATION  OF 

THE  VITELLUS BLASTODERM FORMATION  OF  ORGANS 

IN  THE  FROG. 

Condition  of  the  Mature  Ovarian  Egg — Immediate  Effects  of  Impregnation 
— Disappearance  of  the  Germinative  Vesicle — Nucleus  of  the  Impreg- 
nated Egg — Union  of  the  Spermatozoon  and  Germinative  Vesicle — 
Deposit  of  Albuminous  Layers  in  the  Fallopian  Tube — Segmentation  of 
the  Vitellus— Vitelline  Spheres — Blastoderm — Layers  of  the  Blastoderm 
— Formation  of  Organs — Embryonic  Spot — Area  Pellucida — Primitive 
Trace — Dorsal  Plates — Medullary  Groove — Medullary  Canal — Abdomi- 
nal Plates — Chorda  Dorsalis — Formation  of  the  Cerebro-Spinal  Axis, 
Intestine,  Mouth,  Anus,  and  Limbs — Transformation  of  Tadpole  into  the 
Frog 616-622 

CHAPTER  VII. 

FORMATION    OF    THE    EMBRYO    IN    THE    FOWL'S    EGG. 

Distinctive  Characters  of  Embryonic  Development  in  Birds — The  Yolk  and 
Cicatricula — Segmentation  of  the  Cicatricula  and  Formation  of  the  Blas- 
toderm— Incubation  of  the  Egg,  and  Formation  of  the  Embryo — Exten- 
sion of  the  Blastoderm — Area  Pellucida  and  Primitive  Trace — Formation 
of  the  Blastodermic  Layers — Ectoderm,  Entoderm,  and  Mesoderm — 
Folds  of  the  Blastoderm — Position  of  the  Embryo  in  the  Egg—Dorsal 
Plates,  Medullary  Canal,  and  Cerebro-Spinal  Axis — Protovertebra?, 
Chorda  Dorsalis,  and  Vertebral  Column — Area  Vasculosa,  Blood,  and 
Blood-Vessels 623-638 

CHAPTER  VIII. 

ACCESSORY  EMBRYONIC  ORGANS — UMBILICAL  VESICLE.      AMNION 

AND   ALLANTOIS. 

Office  of  Accessory  Organs  in  the  Development  of  the  Embryo — Umbilical 
Vesicle — In  the  Fish — In  the  Human  Embryo — Amnion  and  Allantois — 
Their  Physiological  Connection — Amniotic  Folds — Amniotic  Cavity — 
Formation  of  the  Allantois— Its  Physiological  Action — Exhalation  of 
Water  by  the  Fowl's  Egg  in  Incubation — Absorption  of  Oxygen  and 
Discharge  of  Carbonic  Acid — Transfer  of  Calcareous  Matter  from  the 
Shell  to  the  Embryo  —  Ossification  of  the  Skeleton  —  Escape  of  the 
Chick  639-644 


XVI  CONTENTS. 

CHAPTER  IX. 

MEMBRANES  OF  THE  IMPREGNATED  EGG  IN  THE  HUMAN  SPECIES. 
AMNION  AND  CHORION. 

PAGE 

Membranous  Envelopes  of  the  Human  Foetus — Amnion— Its  Enlargement — 
Amniotic  Fluid — Chorioii — Early  Formation  of  the  Chorion — Villosities 
of  the  Chorion — Development  of  Blood-Vessels  of  the  Chorion — Partial 
Disappearance  of  its  Villosities— Their  Further  Development  at  the  Sit- 
uation of  the  Placenta 045-649 

CHAPTER  X. 

DEVELOPMENT     OF    THE     DECIDUA,    AND     ATTACHMENT    OF     THE 
FCETAL   MEMBRANES   TO   THE    UTERUS. 

Mucous  Membrane  of  the  Unimpregnated  Uterus — Uterine  Tubules  — 
Decidua  Vera— Hypertrophy  of  the  Uterine  Mucous  Membrane  after 
Impregnation  —  Decidua  Reflexa —  Enclosure  of  Egg  by  the  Decidua 
Reflexa — Attachment  of  the  Egg  to  the  Uterine  Mucous  Membrane — 
Corresponding  Development  of  the  Chorion  and  Decidua  .  .  650-654 

CHAPTER  XI. 

THE    PLACENTA. 

Source  of  Nourishment  for  the  Foetus  in  Man  and  Mammalians — Relations 
of  the  Allantois  and  Uterine  Mucous  Membrane — In  the  Pig — In  Rumi- 
nating Animals — In  Carnivora — In  Man — Vascular  Tufts  of  the  Placenta 
— Vascular  Sinuses  of  the  Decidua — Relation  between  the  Two — Phys- 
iological Action  of  the  Placenta 655-660 

CHAPTER  XII. 

DISCHARGE  OF  THE  FCETUS  AND  PLACENTA.      REGENERATION   OF 
THE    UTERINE    TISSUES. 

Enlargement  of  the  Uterus  during  Pregnancy — Formation  of  the  Umbil- 
ical Cord — Its  Elongation  and  Twisting — Disappearance  of  the  Umbilical 
Vesicle  —  Contact  of  the  Decidua  Vera  and  Reflexa  —  Separation  and 
Discharge  of  the  Foetus  and  Placenta — Hemorrhage  at  the  Time  of 
Delivery  —  Its  Arrest  by  Contraction  of  the  Uterus — Regeneration  <>f 
the  Uterine  Tissues  ul'k-r  Delivery 061-666 

CHAPTER  XIII. 

DEVELOPMENT    OF    THE    NERVOUS     SYSTEM,    ORGANS    OF    SENSE, 
SKELETON,    AND    LIMBS. 

Cerebro-Spinal  Axis — Cerebral  Vesicles — Their  Division — Hemispheres — 
Optic  Thalaini  —  Tuberciila  Quadrigi-mina —  Cerebellum  —  Medulla  Ob- 
]«>iigat  a— Organs  of  Special  Sense  -—Ossification  of  the  Skeleton — Forma- 
tion of  the  Limbs— The  Integument 667-671 


CONTENTS.  XV11 

CHAPTER  XIV. 

DEVELOPMENT  OF  THE   ALIMENTARY  CANAL  AND  APPENDAGES. 

PAGE 

Formation  of  the  Intestinal  Canal  —  Stomach  —  Small  Intestine  —  Large 
Intestine — Convolutions  of  the  Intestine — Anns — Imperforate  Anus — 
Capnt  Coli — Appendix  Vermiformis — Congenital  Umbilical  Hernia — 
Meconiurn — Liver — Lungs,  Thoracic  Cavity,  and  Diaphragm — Urinary 
Bladder  and  Urethra — Development  of  the  Mouth  and  Face  .  .  672-680 

CHAPTER   XY. 

DEVELOPMENT  OF  THE  WOLFFIAN  BODIES,  KIDNEYS,  AND  INTERNAL 
ORGANS  OF  GENERATION. 

Embryonic  Urinary  Apparatus — Wolffian  Bodies — Their  Structure — The 
Kidneys — Internal  Organs  of  Generation — Fallopian  Tubes  and  Vasa 
Deferentia — Descent  of  the  Testicles — Tunica  Vaginalis  Testis — Con- 
genital Inguinal  Hernia — Female  Organs  of  Generation — Descent  of  the 
Ovaries — Formation  of  the  Uterus,  Round  Ligaments  and  Broad  Liga- 
ments— Condition  of  the  Uterus  and  Ovaries  at  Birth  .  .  .  681-686 

CHAPTER  XVI. 

DEVELOPMENT   OF    THE   VASCULAR    SYSTEM. 

Successive  Forms  of  the  Circulatory  System — Vitelline  Circulation — Om- 
phalo-Mesenteric  Vessels  —  Placental  Circulation  —  Umbilical  Arteries 
and  Vein — Adult  Circulation — Development  of  the  Arterial  System — 
Development  of  the  Venous  System  —  The  Hepatic  Circulation  and 
Ductus  Venosus — The  Heart  and  Ductus  Arteriosus — Foramen  Ovale — 
Eustachian  Valve — Crossing  of  Blood-Currents  in  the  Foetal  Heart — 
Changes  in  the  Circulation  at  Birth 687-703 

CHAPTER  XVII. 

DEVELOPMENT   OF   THE   BODY   AFTER   BIRTH. 

Condition  of  the  Newly-Born  Infant — Its  Weight — Establishment  of  Res- 
piration— Condition  of  the  Nervous  System — Relative  Weight  of  the 
Internal  Organs  in  the  Foetus  at  Term  and'the  Adult — Separation  of  the 
Umbilical  Cord  and  Cicatrization  of  the  Umbilicus — Exfoliation  of  the 
Cuticle  and  Hairs — Appearance  of  the  First  Set  of  Teeth — Appearance 
of  the  Second  or  Permanent  Set — Period  of  Puberty,  and  Complete 

Ossification  of  the  Skeleton 704-706 

2 


LIST  OF  ILLUSTRATIONS. 


FIG.  PAGE 

1.  Fibula  tied  in  a  knot,  after  maceration  in  dilute  acid  ....       40 

2.  Grains  of  potato  starch 51 

3.  Saccharomyces  cerevisias,  in  its  quiescent  condition     ....       58 

4.  Saccharomyces  cerevisiae,  in  active  germination  .....       58 

5.  Oleaginous  substances  of  human  fat  . 

6.  Chyle,  from  thoracic  duct  of  the  dog 

7.  Globules  of  cow's  milk       .... 

8.  Hepatic  cells  containing  oil-globules,  human 

9.  Muscular  fibres  of  human  uterus,  three  weeks  after  parturition 

10.  Cholesterine,  from  an  encysted  tumor 

11.  Cells  of  Bacterium  term o  .... 

12.  Hemoglobine  crystals,  from  human  blood  . 

13.  Spectra  of  hemoglobine     .... 

14.  Spectrum  of  green  bile      .... 

15.  Spectrum  of  chlorophylle   .... 

16.  Sodium  glycocholate,  from  ox-bile 

17.  Spectrum  of  Pettenkofer's  test,  with  biliary  s; 

18.  Spectrum  of  Pettenkofer's  test,  with  biliary  sa 

19.  Spectrum  of  Pettenkofer's  test,  with  albumen 

20.  Human  alimentary  canal    .... 

21.  Lobule  of  parotid  gland     .... 

22.  Section  of  submaxillary  gland ;  from  the  dog 

23.  Buccal  and  glandular  epithelium ;  deposited  from  saliva 

24.  Gastric  follicles,  from  pig's  stomach ;  middle  portion 

25.  Portion  of  human  pancreas  and  duodenum 

26.  Hepatic  lobule,  in  transverse  section  . 

27.  Biliary  canals  and  ducts ;  from  the  frog's  liver 

28.  Hepatic  lobule,  transverse  section ;  from  rabbit's  liver 

29.  Duodenal  fistula 

30.  Longitudinal  section  of  wall  of  duodenum 

31.  Portion  of  one  of  Brunner's  glands     . 

32.  Follicles  of  Lieberkiihn      .... 

33.  Contents  of  stomach,  during  digestion  of  meat  . 

34.  Contents  of  duodenum,  during  digestion  of  meat 

35.  Contents  of  middle  portion  of  small  intestine     . 

36.  Contents  of  last  quarter  of  small  intestine 

37.  An  intestinal  villus 

38.  Chyle,  from  thoracic  duct  of  the  dog 

39.  Intestinal  epithelium ;  from  the  dog,  fasting 

40.  Intestinal  epithelium  ;  from  the  dog,  during  digestion 

41.  Capillary  bloodvessels  of  the  intestinal  villi 


. 

65 

.              . 

.        .        . 

67 

. 

. 

67 

. 

, 

68 

ifter  parturition  . 

68 
71 
78 
93 
95 

• 

.     (Funke) 

.         . 

.         . 

100 

> 

. 

103 

. 

108 

ts,  in  watery  solution  . 

112 

;s,  in  alcoholic  solution 

113 

. 

. 

113 

.         . 

.         . 

137 

>m  saliva 

.    (Wagner) 
.  (Kolliker) 

141 
142 
142 

>rtion 

... 

151 

• 

.  (Bernard) 

166 
175 

's  liver 

.     (Eberth) 
.       (Gentli) 

176 
176 
180 

• 

.  (Bernard) 

188 
189 

.         . 

.         .         . 

189 

m 

. 

192 

i 

192 

(Loydi-) 


(Kolliker) 


L08 

197 
198 
198 
199 


xv 


LIST    OF    ILLUSTRATIONS.  XIX 

FIG.  PAGE 

42.  Lacteals  and  lymphatics,  during  digestion 201 

43.  Human  blood -globules „         .         .213 

44.  Red  globules  of  the  blood,  adhering  together 214 

45.  Red  globules  of  the  blood,  shrunken  and  crenated      ....  214 

46.  Red  globules  of  the  blood,  swollen  by  imbibition        ....  215 

47.  Blood-globules  of  the  frog 217 

48.  White  globules  of  the  blood,  altered  by  acetic  acid     ....  220 

49.  Changes  in  form  of  a  white  globule  of  the  blood        ....  220 

50.  Head  and  gills  of  Menobranchus 233 

51.  Lung  of  frog 234 

52.  Human  larynx,  trachea,  bronchi,  and  lungs        .....  234 

53.  Single  lobule  of  human  lung 235 

54.  Capillary  bloodvessels  in  the  pulmonary  vesicles         .         .        (Frey)  235 

55.  Human  larynx,  in  its  post-mortem  condition 238 

56.  Human  larynx,  with  the  glottis  open 238 

57.  Diagram  of  the  circulation  in  mammalians  ......  275 

58.  Right  auricle  and  ventricle ;  ventricular  valves  open,  arterial  valves 

closed '.275 

59.  Right  auricle  and  ventricle ;  ventricular  valves  closed,  arterial  valves 

open 276 

60.  Course  of  the  blood  through  the  heart 276 

61.  Transverse  section  of  the  bullock's  heart  in  cadaveric  rigidity     .         .  280 

62.  Bullock's  heart,  anterior  view ;  showing  superficial  fibres  .         .         .  281 

63.  Converging  spiral  fibres  at  the  heart's  apex 281 

64.  Left  ventricle  of  bullock's  heart ;  showing  deep  fibres        .         .         .  282 

65.  Cardiographic  trace (Marey)  284 

66.  Curvatures  of  an  artery  in  pulsation 287 

67.  Curves  of  pulsation,  in  an  elastic  tube        ......  289 

68.  Trace  of  the  radial  pulse,  taken  by  sphygmograph      .         .         .         .289 

69.  j 

70.  >  Variations  of  the  radial  pulse,  under  the  influence  of  temperature 

71.  ;  (Marey)  290 

72.  Dicrotic  pulse,  in  typhoid  pneumonia         ....      (Marey)  291 

73.  Dicrotic  pulse,  in  typhoid  fever (Marey)  291 

74.  Vein,  with  valves  open      .........  296 

75.  Vein,  with  valves  closed 296 

76.  Small  artery,  breaking  up  into  capillaries 298 

77.  Capillary  bloodvessel (Kolliker)  299 

78.  Capillary  circulation,  in  web  of  frog's  foot 300 

79.  Diagram  of  the  circulation 304 

80.  Crystals  of  uric  acid ;  deposited  from  urine 332 

81.  Ferment-apparatus,  for  saccharine  urine     ....  .  333 

82.  Crystalline  masses  of  sodium  urate;  deposited  from  urine.         .         .  337 

83.  Crystals  of  lime  oxalate ;  deposited  from  urine 339 

84.  Crystals  of  ammonio-magnesian  phosphate;  deposited  from  urine       .  340 

85.  Nerve  fibres,  stained  with  perosmic  acid 345 

86.  Division  of  a  nervous  branch  into  fibres 347 

87.  Division  of  a  nerve  fibre    .........  349 

88.  Interior  bulb  of  Pacinian  body  ....      (Key  and  Retzius)  350 

89.  Sensitive  nerve  fibre  and  end-bulb      .         .         .       (Key  and  Retzius)  351 

90.  Nervous  termination  in  muscular  fibre        ....   (Ranvier)  352 

91.  Nerve  cells  .         .         .         .356 


XX  LIST    OF    ILLUSTRATIONS. 

FIG.  PAGE 

92.  Nerve  cells,  with  capsular  sheaths    .         .         .      (Key  and  Retzius)  357 

93.  Nerve  cell,  with  axis  cylinder  process       .         .      (Key  and  Retzius)  358 

94.  Frog's  leg,  showing  galvanization  of  the  muscles       ....  361 

95.  Frog's  leg,  showing  galvanization  of  the  nerve         ....  302 

96.  Diagram  of  registering  apparatus     .......  368 

97.  Transverse  section  of  the  spinal  cord        ......  374 

98.  Brain  of  alligator 

99.  Brain  of  pigeon 376 

100.  Medulla  oblongata,  and  base  of  the  brain  .         .         .        (Hirschfeld)  377 

101.  Diagrammatic  section  of  the  human  brain 379 

102.  Transverse  sections  of  human  spinal  cord 382 

103.  Transverse  section  of  the  spinal  cord ;  lumbar  region        .         .         .  383 

104.  Transverse  section,  at  the  decussation  of  the  pyramids 

105.  Degeneration  of  divided  nerves  and  nerve  roots        ....  390 

106.  Degeneration  of  the  pyramidal  tracts 395 

107.  Partial  sections  of  spinal  cord,  in  rabbit   .         .         .    (Woroschiloff )  396 

108.  Degeneration  of  columns  of  Goll      .....  (Charcot)  408 

109.  Lateral  sclerosis  of  posterior  columns  of  spinal  cord         .  (Charcot)  408 

110.  Fissures  and  convolutions  of  the  human  brain 414 

111.  Horizontal  section  of  the  human  brain 417 

112.  Vertical  section  of  a  cerebral  convolution        .         .         .      (Ilenle)  418 

113.  Brain  of  the  dog ;  viewed  from  above ;  centres  of  motion        .         .  427 

114.  Brain  of  the  dog ;  viewed  in  profile  ;  "...  428 

115.  Excision  of  angular  convolution ;  leftside 431 

116.  Excision  of  angular  convolution ;  right  side      .....  431 

117.  Brain  of  healthy  pigeon,  profile  view 437 

118.  Brain  of  operated  pigeon,  profile  view 437 

119.  Brain  of  the  cod,  showing  optic  nerves 451 

120.  Brain  of  the  fowl,  showing  optic  nerves  ......  451 

121.  Diagram  of  the  optic  nerves  and  tracts 453 

122.  Lesions  of  the  optic  nerves  and  tracts 454 

123.  Diagram  of  the  fifth  nerve,  and  its  distribution        ....  460 

124.  Diagram  of  the  facial  nerve,  and  its  distribution       ....  469 

125.  Portrait  of  facial  paralysis        ........  472 

126.  Facial  nerve  and  connections,  in  the  aqueduct  of  Fallopius       .         .  475 

127.  Ninth,  tenth,  and  eleventh  cranial  nerves.         .         .        (Hirschfeld)  483 

128.  Ganglia  and  nerves  of  the  sympathetic  system 408 

129.  Distribution  of  nerves  in  the  nasal  passages 517 

130.  Horizontal  section  of  the  right  eyeball 519 

181.  Vision  without  a  lens 524 

132.  Vision  with  a  lens .VJ4- 

133.  Indistinct  image,  from  excessive  refraction .^2~> 

134.  Indistinct  image,  from  deficient  refraction 525 

135.  Rods  and  cones,  of  human  retina     ....  (Schultze)  527 

136.  Surface  of  the  retina,  showing  ends  of  rods  and  cones     (Helmholtz)  528 

137.  Diagram,  for  showing  blind  spot  of  the  retina.         .       (Helmholtz)  530 

138.  Section  of  the  retina,  through  macula  lutea  and  fovea        (Schultze)  532 
130.  Section  of  the  eyeball,  showing  direct  and  indirect  vision         .         .  540 

140.  Catoptric  images  in  the  eye (Helmholtz)  542 

141.  Change    of   position   in    catoptric  images    during    accommodation 

(Helmholtz)  542 

142.  Emmetropic  eye,  in  vision  at  long  distances      .         .         .    (Wundt)  545 


LIST    OF    ILLUSTRATIONS.  Xxi 

FIG-  PAGE 

143.  Myopic  eye,  in  vision  at  long  distances      ....    (Wundt)  545 

144.  Single  and  double  vision,  at  different  distances          ....  547 

145.  Skull,  as  seen  by  the  left  eye     ......  548 

146.  Skull,  as  seen  by  the  right  eye 543 

147.  Rood's  apparatus,  for  measuring  duration  of  electric  spark      .         .  55 1 

148.  Ossicles  of  the  human  ear (Rudinger)  555 

149.  Ossicles  of  the  ear,  in  situ (Rudinger)  556 

150.  Bony  labyrinth  of  the  human  ear     .....  559 

151.  Bony  cochlea  of  the  human  ear        ....      (Cruveilhier)  563 

152.  Organ  of  Corti 555 

153.  Cysticercus  cellulose (Davaine)  575 

154.  Trichina  spiralis ;  encysted       .......  576 

155.  Infusoria,  of  various  kinds       .         .         .         (Ehrenberg  and  Stein)  577 

156.  Stylonychia  mytilus ;  unimpregnated  and  impregnated     .        (Stein)  580 

157.  Cells  of  Bacterium  termo 581 

158.  Human  ovum  ...........  584 

159.  Human  ovum,  ruptured  by  pressure 585 

160.  Female  generative  organs  of  frog 586 

161.  Mature  frog's  eggs 587 

162.  Female  generative  organs  of  fowl 588 

163.  Diagram  of  the  fowl's  egg 589 

164.  Uterus  and  ovaries  of  the  sow 590 

165.  Generative  organs  of  the  human  female  .         .         .         .         .  591 

166.  Spermatozoa 593 

167.  Graafian  follicle,  near  the  period  of  rupture 602 

168.  Ovary  with  Graafian  follicle  ruptured 603 

169.  Human  Graafian  follicle,  ruptured  during  menstruation    .         .         .  609 

170.  Corpus  luteum  of  menstruation,  three  weeks  old      ....  610 

171.  Corpus  luteum  of  menstruation,  four  weeks  old         .         .         .         .  610 

172.  Corpus  luteum  of  menstruation,  nine  weeks  old        .         .         .         .611 

173.  Corpus  luteum  of  pregnancy,  two  months  old 613 

174.  Corpus  luteum  of  pregnancy,  four  months  old           ....  613 

175.  Corpus  luteum  of  pregnancy,  at  term 614 

176.  Segmentation  of  the  vitellus 617 

177.  Impregnated  egg,  with  embryonic  spot    ......  620 

178.  Frog's  egg,  in  an  early  stage  of  development 621 

179.  Frog's  egg,  in  process  of  development 621 

180.  Frog's  egg,  farther  advanced    ........  621 

181.  Tadpole,  fully  developed 621 

182.  Phases  of  segmentation,  in  the  fowl's  egg         .         .         .       (Coste)  625 

183.  Transverse   section   of    the   blastoderm,   showing   its   three   layers 

(Kolliker)  628 

184.  Transverse  section  of  embryo  chick,  showing  open  medullary  groove 

(Kolliker)  630 

185.  Transverse  section  of  embryo  chick,  showing  narrowed  portion  of 

medullary  groove           ......            (Kolliker)  631 

186.  Transverse  section  of  embryo  chick,  showing  closed  medullary  canal 

(Kolliker)  631 

187.  Embryo  chick,  at  thirtieth  hour  of  incubation          .         .    (Kolliker)  632 

188.  Embryo  of  chick,  at  thirty-sixth  hour  of  incubation         .    (Kolliker)  634 

189.  Embryo  of  chick,  about  fortieth  hour  of  incubation         .    (Kolliker)  634 

190.  Portion  of  the  area  vasculosa (Kolliker)  636 


XX11  LIST    OF    ILLUSTRATIONS. 

FIG.  PAGE 

191.  Area  vaseulosa  of  the  embryo  chick 037 

192.  Egg  of  fish,  with  umbilical  vesicle    .......  639 

193.  Human  embryo,  with  umbilical  vesicle      ......  (340 

194.  Fecundated  egg,  showing  formation  of  the  amnion  ....  041 

in.").  Fecundated  egg,  farther  advanced 041 

196.  Fecundated  egg,  with  allantois  nearly  complete         ....  042 

T.»7.    1'Vcundated  egg,  with  allantois  fully  formed (',[-2 

198.  Human  embryo  and  envelopes ;   end  of  first  month  ....  045 

!!»'.'.  Human  embryo  and  envelopes ;  end  of  third  month         .        .        .  r»45 

200.  Compound  villosity  of  the  chorion 047 

201.  Extremity  of  a  villosity  of  the  chorion     ......  047 

202.  Uterine  mucous  membrane;  unimpregnated  uterus  ....  650 

203.  Uterine  tubules;  unimpregnated  uterus    ......  650 

204.  Impregnated  nterna ;  formation  of  decidua  vera       ....  fir>2 

205.  Impregnated  uterus ;  formation  of  decidua  reflexa  ....  i'>-">2 

206.  Impregnated  uterus;  egg  inclosed  by  decidua  retlexa        .         .         .  O.V2 

207.  Impregnated  uterus;  connection  of  egg  and  decidua         .         .         .  653 

208.  Pregnant  uterus ;  formation  of  the  placenta 653 

209.  Extremity  of  a  foetal  tuft,  from  human  placenta        ....  0-"i7 

210.  Extremity  of  a  foetal  tuft,  injected iio7 

211.  Diagram  of  the  placenta,  in  vertical  section 658 

212.  Human  embryo  and  its  inembran*              ......  661 

213.  Pregnant  human  uterus,  at  the  seventh  month           ....  r»o2 

214.  Muscular  fibres  of  the  unimpregnated  uterus 604 

215.  Muscular  fibres  of  the  uterus,  ten  days  after  parturition    .         .         .  005 
210.  Muscular  fibres  of  the  uterus,  three  weeks  after  parturition      .         .  005 

217.  Formation  of  the  cerebro-spinal  axis 667 

218.  Formation  of  the  cerebral  vesicles    .......  007 

219.  Foetal  pig,  showing  brain  and  spinal  cord 007 

220.  Foetal  pig,  farther  advanced      ........  668 

221.  Head  of  fo3tal  pig,  showing  hemispheres,  cerebellum,  and  medulla 

oblongata      . 608 

222.  Brain  of  adult  pig r,i;i) 

223.  Human  embryo,  one  month  old         .         .         .         .         .         .  (171 

224.  Formation  of  the  alimentary  canal 672 

225.  Foatal  pig,  showing  umbilical  hernia 674 

226.  Human  embryo,  showing  development  of  the  face    ....  07* 

227.  Head  of  human  embryo,  about  the  sixth  week          ....  U79 

228.  Head  of  human  embryo,  at  end  of  second  month     ....  0711 

229.  Foetal  pig,  showing  Wolffian  bodies OSL 

230.  Foetal  pig,  showing  Wolffian  bodies  and  kidneys       ....  682 

231.  Internal  organs  of  generation,  in  the  foetal  pig          ....  683 

232.  Internal  organs  of  generation,  in  the  foetal  pig,  farther  advanced 

233.  Formation  of  tunica  vaginalis  testis 684 

234.  Congenital  inguinal  hernia 685 

235.  Egg  of  fish,  showing  vitelline  circulation            .....  687 
230.   Diagram  of  the  embryo,  with  umbilical  vesicle  and  allantois     .          .  688 
237.  Diagram  of  the  embryo,  showing  the  plaeental  circulation        .         .  689 

Venous  system,  in  its  earliest  condition 693 

239.  Venous  system,  farther  advanced      .......  693 

240.  Venous  system,  more  fully  developed ti'.c>, 

241.  Venous  system,  adult  condition till}- 


LIST    OF    ILLUSTRATIONS.  XX111 

FIG.  PAGE 

242.  Early  form  of  the  hepatic  circulation        ......  695 

243.  Hepatic  circulation,  farther  advanced        .  695 

244.  Hepatic  circulation,  in  latter  part  of  foetal  life 696 

245.  Hepatic  circulation,  adult  condition  .......  696 

246.  Foetal  heart,  earliest  form 697 

247.  Foetal  heart,  bent  upon  itself 697 

248.  Foetal  heart,  farther  advanced 697 

249.  Heart  of  infant 698 

250.  Heart  of  human  foetus,  at  sixth  month 699 

251.  Diagram  of  foetal  circulation  through  the  heart        ....  700 

252.  Diagram  of  adult  circulation  through  the  heart        .         .         .         .  702 


VALUE  OF  WEIGHTS  AKD  MEASURES 

ACCORDING   TO   THE   METRIC   SYSTEM,    EMPLOYED   IN   THIS   BOOK. 

One  gramme =  15.434  grains. 

One  kilogramme  (1000  grammes)  =  2.2  pounds  Avoirdupois. 


One  micromillimetre    .     .     .     .     =  0.00004  (asSoo)  mch- 

One  millimetre =0.0394       (^)       " 

One  centimetre =  0.394 


One  cubic  centimetre  .     .     .     .     =0.061  cubic  inch. 

One  litre  (1000  c.  c.)     .     .     .     .     =  61  cubic  inches  (0.035  cubic  foot). 


XXIV 


HUMAN  PHYSIOLOGY. 


INTEODUCTION. 

PHYSIOLOGY  is  the  study  of  the  phenomena  of  life.  It  makes  us 
acquainted  with  their  immediate  causes,  the  conditions  of  their 
manifestation,  the  material  changes  in  the  body  by  which  they  are 
accompanied,  their  mechanism,  and  their  results.  It  teaches  us  all 
that  can  be  known  of  the  living  organism  in  a  state  of  activity,  with 
its  different  parts  performing  their  appropriate  functions,  and  the  whole 
structure  exhibiting  the  characters  of  individuality  and  life. 

In  physiology,  as  in  all  the  other  natural  sciences,  direct  observation 
is  the  only  means  by  which  actual  knowledge  can  be  attained.  Ample 
experience  has  demonstrated  that  in  these  departments  analogical 
deductions  and  inferences  are  unsafe,  and  that  every  question  must  be 
tested  by  experimental  investigation.  Even  the  anatomical  structure 
of  an  organ  can  never  indicate  with  certainty  its  physiological  proper- 
ties, until  by  immediate  examination  we  have  found  the  function  to  be 
associated  with  the  structure.  This  method,  which  depends  entirely 
upon  observation,  is  laborious  and  difficult;  but  it  is  the  method  to 
which  we  owe  all  our  present  knowledge  of  natural  phenomena, 
and  the  only  one  which  can  produce  similar  results  in  the  future. 
There  are  some  special  considerations  regarding  its  application  to 
physiology,  owing  to  the  intricate  constitution  of  organized  beings, 
and  the  complexity  of  their  functions. 

The  entire  body  is  a  composite  structure,  made  up  of  many  parts 
with  varied  characters  and  properties ;  and  the  life  of  the  organism  as 
a  whole  depends  on  the  combined  activity  of  its  different  parts.  Conse- 
quently each  one  of  these  should  be  first  studied  by  itself,  in  order  to  ascer- 
tain, so  far  as  possible,  its  individual  characters.  This  may  be  done  in 
great  measure  by  the  examination  of  single  parts,  separated  from  the 
rest ;  because  minute  anatomical  structures,  like  muscular  fibres  or  nerve 
fibres,  owe  their  distinguishing  properties  directly  to  the  nature  and 

25 


26  INTRODUCTION. 

combination  of  their  constituent  materials.  So  long  as  they  are  con- 
nected with  the  living  organism,  their  physical  constitution  is  main- 
tained by  the  supply  of  nutriment  from  the  blood  and  interstitial 
fluids.  But  after  this  supply  is  cut  off,  they  still  remain  for  a  time 
sufficiently  unaltered  to  exhibit  their  specific  characters.  By  this 
means  we  learn  that  the  physiological  property  of  a  muscular  fibre 
is  contractility ;  and  that  there  are  two  kinds  of  these  fibres,  the 
striped  and  the  unstriped,  both  of  which  contract  under  the  application 
of  a  stimulus,  but  with  different  degrees  of  rapidity.  A  nerve  fibre, 
on  the  other  hand,  has  the  power  of  transmitting  a  stimulus  to  distant 
regions,  and  of  calling  into  activity  other  parts  with  which  it  is  con- 
nected. In  certain  instances  the  action  and  products  of  special  gland- 
ular tissues  may  be  studied  with  some  success  in  a  similar  way.  As 
a  general  rule,  investigations  of  this  kind  are  most  readily  carried  out 
in  the  cold-blooded  animals ;  because  their  tissues  are  the  seat  of  a 
less  rapid  alteration  than  in  the  warm-blooded  classes,  and  retain  their 
normal  properties  for  a  longer  time  after  separation  from  the  body. 

But  the  functional  activity  of  entire  organs,  or  of  an  apparatus  of 
associated  organs,  can  be  studied  only  by  experimental  observation 
upon  the  living  body.  A  compound  structure  produces  results  in  which 
all  its  various  parts  have  their  share,  and  which  are  affected  by  the 
manner  in  which  these  parts  are  combined  in  successive  or  simultaneous 
action.  Thus  every  muscular  fibre  in  the  walls  of  the  heart  has  the 
same  simple  property  of  contractility ;  but  the  physical  action  of  the 
organ,  as  a  whole,  is  produced  by  so  many  contractile  fibres,  arranged 
in  so  complex  a  form,  that  it  needs  a  direct  inspection  of  the  living 
heart  to  show  the  character,  rhythm,  and  frequency  of  its  pulsations. 
The  glandular  organs  yield  secretions  which  contain  not  only  the  special 
products  of  their  cells,  but  also  materials  supplied  from  the  circu- 
lating blood;  and  this  supply  varies  in  quantity  and  composition 
according  to  different  nervous  and  vascular  conditions.  In  the  digestive 
apparatus  a  number  of  secretions  act,  in  succession  or  together,  upon 
the  elements  of  the  food,  and  thus  modify  the  properties  derived  from 
their  individual  composition.  These  facts  make  it  necessary,  in  the 
solution  of  the  most  important  questions,  to  study  the  animal  functions 
by  means  of  observation  and  experiment  during  life. 

The  progress  of  physiology  at  the  present  day  is  characterized  by 
the  general  adoption  of  methods  which  yield  results  in  many  respects 
more  definite  and  positive  than  those  formerly  attained.  This  is  laruvly 
due  to  the  improvements  in  physics  and  chemistry,  which  place  at  the 
disposal  of  the  physiologist  more  effective  means  of  investigation. 
Many  of  the  phenomena  presented  by  living  bodies  can  now  be  exam- 
ined, measured,  and  recorded  by  the  aid  of  optical,  electrical,  photo- 
graphic and  registering  instruments,  by  which  our  knowledge  in  regard 
to  them  is  rendered  both  more  extensive  and  more  precise.  We  aro 
also  enabled  by  this  means  to  compare  the  results  of  different  observa- 
tions, and  to  reach  the  important  deductions  based  on  the  relation  of 


INTRODUCTION.  27 

quantities.  This  seems  to  be  still  the  most  imperfect  department  of 
the  subject,  and  one  in  which  we  are  most  liable  to  hasty  conclusions 
from  insufficient  data ;  but  the  method  is  one  of  great  promise,  and 
has  already  produced  much  certain  and  useful  information.  The  animal 
functions  are  examined  in  every  way  in  which  they  are  accessible  to 
physical  and  numerical  investigation.  The  structure  of  each  organ, 
and  the  constituent  materials  of  its  tissues,  are  determined  by  appro- 
priate means.  The  changes  in  its  volume,  temperature,  vascularity, 
and  composition,  the  nature  and  quantity  of  the  materials  consumed 
and  of  the  force  manifested,  are  ascertained  and  registered.  The  new 
substances  produced  are  tested  and  measured,  and  the  accompanying 
changes  in  other  organs,  or  in  the  whole  body,  are  subjected  to  similar 
examination. 

In  this  way  the  physiologist  studies  the  living  body  as  a  machine. 
He  endeavors  to  learn  the  construction  of  its  parts,  the  mechanism  of 
their  action,  the  materials  with  which  it  is  supplied,  the  chemical  trans- 
formations of  its  internal  nutrition,  and  the  phenomena  which  it  ex- 
hibits in  every  department  of  the  vital  operations.  For  this  purpose 
he  employs  all  the  available  means  of  scientific  investigation. 

A  large  part  of  the  phenomena  presented  by  living  creatures  are 
general  in  character,  and  show  themselves  in  all  classes  of  vegetable 
and  animal  organisms.  The  absorption  of  new  material  and  the  dis- 
charge of  waste  products,  indicating  the  incessant  renovation  of  the 
organized  fabric,  and  the  direct  relation  between  the  quantity  of  nutri- 
ment consumed  and  the  active  manifestation  of  vitality,  are  noticeable 
facts  in  every  form  of  animated  existence.  Some  of  the  materials  and 
conditions  necessary  to  life  are  the  same  in  all  cases.  The  consumption 
of  oxygen  and  the  discharge  of  carbonic  acid  are  universal  phenomena, 
both  in  animals  and  vegetables.  The  presence  and  absorption  of  moist- 
ure are  also  indispensable  conditions;  and  in  every  case  there  are 
certain  limits  of  temperature  which  cannot  be  overpassed  in  either 
direction  without  disturbance  or  arrest  of  the  vital  operations.  The 
general  nature  of  these  conditions  shows  their  fundamental  impor- 
tance in  the  phenomena  of  life,  and  requires  a  certain  acquaintance 
with  vegetable  physiology  as  an  aid  to  the  more  successful  study  of 
the  animal  functions. 

On  the  other  hand,  there  are  some  special  forms  of  vital  activity 
which  are  confined  to  vegetables,  and  others  which  are  met  with  only 
in  animals.  Thus,  the  deoxidation  of  carbonic  acid  and  water,  together 
with  the  combination  of  their  remaining  elements  to  form  organic  mate- 
rials, can  be  accomplished  only  by  the  living  tissues  of  green  vege- 
tables ;  animals  having  no  power  to  produce  organic  matter,  but  only  to 
consume  it.  Furthermore,  it  is  only  in  the  higher  animals  that  con- 
sciousness, sensation,  and  volition  appear  to  have  a  distinct  existence, 
and  come  into  prominence  in  connection  with  the  functions  of  the 
nervous  system.  In  the  animal  kingdom  certain  materials  or  modes  of 
activity  are  so  nearly  the  same  in  many  different  classes  as  to  indicate 


28  INTRODUCTION. 

a  close  relation  with  some  common  feature  of  their  organization ; 
while  others,  on  the  contrary,  are  confined  to  two  or  three  species  alone. 
Thus,  the  red  coloring  matter  of  the  blood  is  identical  in  color,  general 
composition,  optical  properties,  and  physiological  action  throughout  the 
different  groups  of  quadrupeds,  birds,  reptiles,  and  fish ;  in  all  of  them 
the  nerve  fibres  have  the  same  distinctive  endowments  of  motor  and 
sensitive  qualities,  and  the  internal  reactions  are  performed  by  the  nerve 
centres  in  a  similar  way.  But  the  power  of  producing  electric  shocks 
exists  only  in  a  few  species  of  fish,  which  resemble  in  all  other  respects 
the  fishes  which  are  non-electric.  Both  the  general  nature  of  the  more 
common  functions,  and  the  specific  character  of  those  which  are 
exceptional,  become  legitimate  sources  of  knowledge  in  physiological 
science. 

The  physiology  of  the  human  species  includes  all  the  more  general 
and  fundamental  facts  common  to  man  and  animals,  as  well  as  the 
specific  differences  peculiar  to  the  human  organism.  These  differences, 
as  a  general  rule,  do  not  relate  to  the  character  of  the  vital  phenomena 
nor  to  their  mode  of  production,  but  only  to  their  quantity  or  intensity. 
Thus  the  animal  heat,  produced  in  the  living  tissues,  is  generated  no 
doubt  by  processes  of  the  same  kind  in  the  human  species  as  in  quad- 
rupeds ;  but  the  exact  temperature  of  the  human  body,  and  its  normal 
variations,  are  to  be  determined  by  direct  observation  upon  man.  The 
consumption  of  oxygen  and  the  exhalation  of  carbonic  acid  take  place 
in  essentially  the  same  manner  in  man  as  in  the  higher  animals  ;  but 
the  precise  quantity  of  each,  and  their  numerical  relation  to  other  ingre- 
dients or  products  of  the  body,  are  peculiar  to  man  and  must  be  ascer- 
tained by  special  examination.  Nearly  all  the  observations,  therefore, 
requiring  to  be  made  upon  the  human  subject,  relate  to  matters  of  detail, 
most  of  the  general  and  fundamental  facts  being  reached  by  investiga- 
tions in  the  physiology  of  animals.  The  exceptions  to  this  rule  are 
mainly  connected  with  certain  functions  of  the  nervous  system,  which 
are  so  highly  developed  in  man,  as  compared  with  the  animals,  that  their 
activity  becomes  different  in  kind  as  well  as  in  degree.  Thus  the 
faculty  of  articulate  language,  which  has  no  existence  in  animals,  has 
been  localized  in  a  particular  region  of  the  brain,  wholly  by  means  of 
observations  upon  man;  and  it  is  probable  that  the  same  methods  will 
be  requisite  in  regard  to  some  other  of  the  nervous  functions.  But  in 
most  respects  the  phenomena  of  human  physiology  are  intimately  con- 
nected with  those  of  the  higher  animals. 

The  study  of  physiology  is  naturally  divided  into  several  depart- 
ments or  sections,  each  of  which  deals  with  certain  special  subjects, 
and  is  distinguished  by  the  nature  of  the  facts  investigated,  the 
methods  by  which  they  are  examined,  and  their  relation  to  the  vital 
activity  of  the  whole  body. 

The  first  section  is  devoted  to  Physiological  Chemistry.  It  com- 
prises the  study  of  the  chemical  ingredients  of  the  living  body,  their 
composition  and  reactions,  the  source  from  which  they  are  derived,  their 


INTRODUCTION.  29 

quantity  and  distribution  in  the  animal  frame,  their  occurrence  as  con- 
stituent parts  of  the  food,  their  combinations  and  decompositions  in  the 
body,  and  the  form  under  which  they  appear  in  the  products  of  excre- 
tion. It  aims  to  give  a  general  view  of  the  materials  supplied  to  the 
animal  organism,  and  the  use  which  they  subserve  in  the  processes 
of  life. 

The  second  section  treats  of  the  functions  of  Nutrition.  It  includes 
the  action  of  the  digestive  apparatus,  by  which  the  food  is  prepared 
for  assimilation,  the  absorption  of  the  digested  products,  their  elabora- 
tion in  the  glandular  organs,  the  blood  and  its  circulation,  the  forma- 
tion and  character  of  the  secretions,  the  phenomena  of  respiration,  the 
production  of  animal  heat,  and  the  constitution  and  properties  of  the 
excreted  fluids.  These  processes  have  for  their  object  the  vegetative 
growth  and  renovation  of  the  body,  or  the  maintenance  of  its  normal 
structure  and  organization.  They  are  for  the  most  part  of  a  physical 
or  chemical  nature,  and  are  distinguished  from  other  physical  or  chem- 
ical phenomena  only  by  the  variety  and  complexity  of  their  results. 

The  third  division  in  the  natural  order  of  study  embraces  the  func- 
tions of  the  Nervous  System.  These  functions  are  of  a  different 
character  from  the  preceding,  and  are  investigated  by  different  means. 
The  two  groups  of  phenomena  are  thus  distinguished  from  each  other, 
notwithstanding  the  fact  that  they  are  mutually  dependent.  The 
activity  of  the  nervous  system  requires  for  its  support  a  continued 
nutrition;  and  on  the  other  hand  the  influence  of  the  nervous  system  is 
everywhere  felt  by  the  organs  of  circulation  and  secretion.  But  the 
immediate  action  of  the  nervous  system  is,  so  far  as  we  can  judge,  of 
a  special  nature,  and  one  which  has  no  resemblance  to  the  nutritive 
operations.  It  is  a  means  of  sympathetic  communication,  by  which  the 
different  organs  are  alternately  stimulated  or  controlled,  and  which  acts 
as  the  instrument  of  sensibility,  consciousness,  volition,  and  movement. 
It  brings  the  living  body  into  active  relation  with  the  external  world, 
and  provides  for  the  exercise  of  the  animal  instincts  and  powers. 

The  last  group  of  functions  contains  those  belonging  to  Reproduc- 
tion. They  are  made  up  of  phenomena,  different  in  kind  from  either 
of  the  foregoing,  and  having  for  their  object  the  continuation  of  the 
species.  They  consist  in  the  production,  from  the  parent  organism, 
of  the  sexual  elements,  and  in  the  appearance,  from  the  union  of  these 
elements,  of  a  progressive  series  of  organic  forms,  following  each 
other  in  a  determinate  order  of  successive  transformations,  until  the 
last  form  in  the  series  reproduces  that  of  the  original  parent.  The 
distinguishing  feature  of  this  process  is  therefore  that  the  functions 
of  nutrition  and  growth  are  here  directed  by  a  law  of  continuous  devel- 
opment ;  and  it  presents,  as  the  main  object  of  our  study,  the  form  and 
structure  of  the  different  parts  as  they  successively  appear  in  the  grow- 
ing organism. 


SECTION  I. 

PHYSIOLOGICAL  CHEMISTRY. 


CHAPTER  I. 
CHEMICAL  INGREDIENTS  OF  THE  BODY. 

THE  first  requisite,  in  the  study  of  the  vital  operations,  is  a  knowl- 
edge of  the  substances  which  make  up  the  animal  frame.  It  is  these 
substances  which  give  to  the  organic  tissues  and  fluids  their  specific 
character  ;  and  the  manner  in  which  they  are  supplied,  and  the  changes 
which  they  undergo  within  the  body,  constitute  the  basis  of  all  the 
properties  which  distinguish  the  living  structure. 

If  we  examine  any  one  of  the  fluids  contained  in  various  parts  of  the 
body,  such  as  the  blood,  the  lymph,  the  bile  or  the  saliva,  we  find  that 
it  is  made  up  of  a  number  of  different  ingredients,  mingled  together  in 
certain  proportions.  Thus  the  blood  contains  albuminous  matters  and 
water,  together  with  calcareous  or  alkaline  chlorides,  carbonates,  and 
phosphates.  In  the  bile  there  are  biliary  salts,  coloring  matters,  choles- 
terine,  and  mineral  substances ;  and  the  saliva  is  a  mixed  solution  of 
albuminous  and  saline  ingredients.  The  proportion  of  these  ingredi- 
ents, in  each  animal  fluid,  is  maintained  by  the  process  of  nutrition  at 
about  the  same  standard;  those  which  are  expended  and  lost  in  the  vital 
operations  being  replaced  by  others  of  the  same  kind  derived  from  the 
food  or  produced  by  the  transformation  of  other  materials. 

There  is  a  similar  association  of  different  ingredients  in  the  solid  parts 
of  the  body.  Even  where  the  animal  tissue  appears  most  homogeneous, 
it  contains  a  variety  of  materials,  and  it  is  probable  that  the  minutest 
fibre  or  membrane  in  the  system  is  made  up  in  the  same  way  of  several 
constituents.  In  the  hard  substance  of  bone,  for  example,  there  is 
water,  which  may  be  expelled  by  evaporation ;  lime  phosphate  and  car- 
bonate, which  may  be  extracted  by  solvents ;  a  peculiar  animal  matter, 
with  which  the  calcareous  salts  are  in  union  ;  and  various  other  saline 
substances,  in  special  proportions.  The  muscular  tissue  contains  water, 
sodium  and  potassium  chlorides,  lime  phosphate,  creatine,  albumen,  col- 
oring matter, and  myosine.  It  is  the  object  of  physiological  chemistry 
to  isolate  these  different  substances  from  each  other,  to  study  their  spe- 
cific properties,  and  to  learn  the  part  taken  by  each  in  the  act  of 
nutrition. 

But  it  is  very  important  in  this  investigation  to  determine  what  are 
the  real  ingredients  of  the  animal  frame,  and  to  distinguish  them  from 

30 


CHEMICAL    INGREDIENTS    OF    THE    BODY.  31 

the  abnormal  products  of  their  change  or  decomposition.  The  substances 
in  question  must  be  extracted  from  the  tissues  and  fluids  of  the  body 
by  the  aid  of  physical  and  chemical  manipulations,  such  as  evaporation, 
solution,  precipitation,  and  crystallization.  Many  of  them  are  of  a  nature 
to  be  altered  or  decomposed  by  the  treatment  to  which  they  are  subjected, 
or  even  by  the  unnatural  conditions  resulting  from  the  cessation  of  life. 
The  coagulable  substances  of  the  blood  and  of  the  muscular  tissue,  which 
are  fluid  during  life,  soon  after  death  pass  into  the  solidified  condition, 
and  thus  no  longer  present  their  original  characters.  The  red  coloring 
matter  of  the  blood  requires  to  be  extracted  at  a  temperature  nearly  as 
low  as  the  freezing  point  of  water,  otherwise  it  loses  its  natural  com- 
position and  becomes  changed  into  other  substances.  The  normal 
coloring  matter  of  the  retina  is  bleached  by  the  action  of  daylight, 
and  so  disappears  altogether  unless  special  precautions  be  used  for  its 
protection.  This  sensibility  of  the  organic  ingredients,  making  them 
liable  to  be  affected  by  unnatural  conditions,  is  the  reason  why  many 
of  them  have  long  remained  unknown  or  misunderstood ;  and  it  also 
accounts  in  great  measure  for  the  changing  nomenclature  of  physiological 
chemistry.  By  improved  methods  of  extraction,  an  organic  ingredient 
is  often  obtained  in  a  new  form,  which  more  fully  represents  its  normal 
character ;  and  it  therefore  receives  a  different  name,  to  distinguish  it 
from  the  former  substance.  Thus,  the  coloring  matter  of  the  red  blood- 
globules,  formerly  known  as  "hematine,"  was  obtained  from  the  blood 
in  an  insoluble  condition  by  the  use  of  heat  and  acids.  Subsequently, 
when  extracted  by  the  simpler  action  of  water  and  alcohol,  at  low 
temperatures,  retaining  its  natural  color,  solubility,  and  spectroscopic 
character,  it  was  named  "  hernoglobine,"  and  was  recognized  as  the 
real  constituent  of  the  red  globules. 

The  physiological  ingredients,  therefore,  of  the  animal  frame  are 
substances  which  exist  in  its  solids  or  fluids  under  their  own  form,  and 
are  obtained  by  means  which  do  not  change  them  into  other  matters 
or  decompose  them  into  their  chemical  elements.  Lime  phosphate, 
for  instance,  is  an  immediate  constituent  of  the  bony  tissue,  but  phos- 
phoric acid  is  not  so,  for  it  is  not  present  under  its  own  form,  but  is 
obtained  only  by  breaking  up  its  combination  with  the  calcareous  mat- 
ter ;  while  phosphorus  is  a  product  of  still  further  decomposition  of  the 
phosphoric  acid.  An  animal  substance  containing  the  alkaline  acetates 
or  lactates,  if  treated  by  incimeration  in  the  air,  would  yield  as  a  residue 
the  carbonates  of  the  same  bases,  the  original  organic  acids  having  been 
destroyed  and  replaced  by  carbonic  acid.  As  a  rule,  accordingly,  in  the 
examination  of  animal  tissues,  the  simplest  forms  of  chemical  manipu- 
lation are  most  successful.  The  substance  or  fluid  is  first  subjected  to 
evaporation,  in  order  to  extract  and  estimate  its  water.  The  evap- 
oration is  conducted  at  a  heat  not  above  100°  C,  or  the  boiling  point 
of  water,  since  a  higher  temperature  would  often  be  injurious  to  the 
organic  ingredients.  From  the  dried  residue  sodium  chloride,  alkaline 
sulphates,  carbonates,  and  phosphates  are  extracted  with  water.  Coloring 


32  PHYSIOLOGICAL     CHEMISTRY. 

matters  are  usually  separated  by  alcohol,  and  oils  may  be  dissolved  out 
by  ether.  When  a  chemical  decomposition  is  unavoidable,  it  must  be 
kept  in  sight  and  afterward  corrected.  Thus,  the  sodium  glycocholate 
of  the  bile  is  separated  from  certain  other  ingredients  by  precipitating 
it  with  plumbic  acetate,  forming  lead  glycocholate  ;  but  this  is  afterward 
decomposed  in  turn  by  sodium  carbonate,  reproducing  the  original 
sodium  glycocholate.  Certain  organic  materials  of  peculiar  physiological 
activity  are  extracted  by  means  of  glycerine,  which  preserves  them  in- 
definitely in  an  unaltered  condition  ;  and  as  a  general  rule  the  improve- 
ments in  this  branch  of  investigation  consist  in  exact  regulation  of  the 
temperature,  the  avoidance  of  strong  acid  and  alkaline  reagents,  the 
employment  of  mild  solvents  and  precipitating  solutions,  and  in  especial 
care  that  the  substance  to  be  examined  is  obtained  in  a  fresh  condition, 
unchanged  by  cadaveric  alterations.  By  this  means  we  may  form  a 
tolerably  correct  estimate  of  the  nature,  quantity,  and  properties  of  the 
constituent  materials  of  the  living  organism. 

The  manner  in  which  these  ingredients  are  associated  together  is  also 
deserving  of  notice.  In  every  animal  solid  and  fluid,  there  is  a  number 
of  different  substances  present  in  certain  proportions,  so  united  with 
each  other  that  the  mixture  presents  a  homogeneous  appearance.  But 
this  union  is  of  a  complicated  character ;  and  the  presence  of  each  in- 
gredient depends,  to  a  certain  extent,  upon  that  of  the  others.  Some 
of  them,  such  as  the  alkaline  carbonates  and  phosphates,  are  in  direct 
solution  in  the  water.  Some,  which  are  insoluble  in  water,  are  retained 
in  solution  by  the  presence  of  other  soluble  substances.  Thus,  the 
insoluble  lime  phosphate  of  the  urine  is  held  in  solution  by  the  acid 
sodium  biphosphate,  also  present  as  an  ingredient.  In  the  alkaline 
blood-plasma,  on  the  other  hand,  the  lime  phosphate  is  liquefied  by 
union  with  the  albumen,  which  is  itself  soluble  in  the  water  of  the 
plasma.  The  same  substance  may  be  fluid  in  one  part  of  the  body, 
and  solid  in  another  part.  Thus,  in  the  blood  and  secretions  the 
water  is  fluid,  and  holds  other  substances  in  solution ;  while  in  the 
bones  and  cartilages  it  is  solid,  by  its  union  with  the  animal  and 
saline  ingredients,  abundantly  present  in  the  solid  form.  In  the  blood, 
the  lime  phosphate  is  fluid  by  solution  in  the  albumen ;  but  in  the 
bones  it  forms  a  solid  substance  with  the  animal  matter  of  the 
osseous  tissue ;  and  the  union  of  the  two  is  as  intimate  and  homo- 
geneous in  the  bones  as  in  the  blood.  4n  animal  ingredient,  there- 
fore, never  exists  alone  in  any  part  of  the  body,  but  is  always 
associated  with  a  number  of  others,  by  homogeneous  mixture  or 
mutual  solution. 

The  proportion  in  which  each  ingredient  is  present,  in  any  animal 
solid  or  fluid,  is,  as  a  rule,  characteristic  of  that  tissue  or  secretion, 
and  contributes  largely  to  its  physiological  characters.  Thus,  water 
is  present  in  large  quantity  in  the  perspiration  and  the  saliva,  but  in 
small  quantity  in  the  bones  and  teeth.  Sodium  chloride  is  compara- 
tively abundant  in  the  blood  and  deficient  in  the  muscles.  On  the 


CHEMICAL    INGREDIENTS    OF    THE    BODY.  33 

other  hand,  potassium  chloride  is  more  abundant  in  the  muscles,  less 
so  in  the  blood.  But  these  proportions  are  nowhere  absolute  or  in- 
variable. There  is  a  difference,  in  this  respect,  between  the  chemical 
composition  of  an  inorganic  substance  and  the  physiological  constitu- 
tion of  an  animal  fluid.  The  former  is  constant  and  definite  ;  the  latter 
always  presents  certain  variations.  Thus,  water  is  invariably  com- 
posed of  the  same  relative  quantities  of  hydrogen  and  oxygen ;  and 
these  proportions  are  essential  to  its  existence.  But  in  the  urine,  the 
proportions  of  water,  urea,  urates,  and  phosphates  vary  within  certain 
limits  in  different  individuals,  and  even  in  the  same  individual,  from 
one  hour  to  another.  This  physiological  variation  takes  place,  within 
the  limits  of  health,  in  all  the  animal  solids  and  fluids.  It  is  a  necessary 
accompaniment  of  the  actions  of  life,  and  one  of  the  characteristic  phe- 
nomena of  living  beings.  The  animal  body  is  the  seat  of  incessant 
changes,  and  all  its  manifestations  of  vital  activity  are  either  the 
causes  or  the  result  of  its  internal  alterations.  Every  variation  in  its 
general  condition  is  accompanied  by  a  corresponding  variation  in  the 
constitution  of  its  different  parts.  This  constitution  is  consequently  of 
a  very  different  character  from  the  chemical  constitution  of  an  oxide  or  a 
salt.  In  the  analysis  of  an  animal  tissue  or  fluid,  the  numbers  express- 
ing the  proportion  of  its  different  ingredients  are  always  understood  to 
be  approximate,  and  not  absolute.  They  represent  the  general  character 
of  the  mixture,  but  allow  of  its  variation  within  physiological  limits. 

The  chemical  ingredients  of  the  body  are  naturally  divided  into  five 
classes : 

The  first  of  these  classes  comprises  all  ingredients  of  a  purely 
INORGANIC  nature.  These  substances  are  derived  mostly  from  the  exte- 
rior. They  are  found  abundantly  in  the  inorganic  world  as  well  as 
in  organized  bodies ;  and  they  present  themselves  under  the  same  form 
and  with  the  same  properties  in  the  interior  of  the  animal  frame  as 
elsewhere.  They  are  crystallizable,  with  definite  chemical  characters 
and  a  simple  chemical  constitution.  They  are  compounds,  in  simple 
proportions,  of  hydrogen  and  oxygen,  the  metals  of  the  alkaline  and 
earthy  salts,  sulphur,  phosphorus,  chlorine,  and,  in  general  terms,  of 
the  ingredients  of  mineral  substances.  They  comprise  water,  which  is 
the  most  abundant  of  its  class  in  the  animal  frame,  sodium  and  potas- 
sium chlorides,  phosphates,  and  sulphates,  alkaline  carbonates,  the  salts 
of  lime  and  magnesia,  together  with  combinations  of  a  few  other  metallic 
elements  in  small  quantity. 

The  second  class  consists  of  the  HYDRO-CARBONACEOUS  SUBSTANCES  of 
organic  origin.  They  are  distinguished  from  inorganic  matters  first  by 
the  fact  of  their  containing  carbon  in  large  proportion  as  one  of  their 
immediate  constituents,  associated  with  hydrogen  and  oxygen,  but 
with  no  other  chemical  element.  They  are  either  crystallizable  or 
readily  convertible  into  other  crystallizable  members  of  the  same  group. 
Their  chemical  composition  is  less  simple  than  that  of  inorganic  sub- 
stances, but  it  is  still  sufficiently  definite,  and  their  chemical  characters 

C 


34  PHYSIOLOGICAL    CHEMISTRY. 

are  well  marked  and  easily  recognizable.  They  first  make  their  appear- 
ance in  the  interior  of  organized  bodies,  and  are  not  found  in  the  inor- 
ganic world,  excepting  as  the  remains  or  products  of  animal  or  vege- 
table life.  To  this  group  belong  the  several  varieties  of  starch,  sugar, 
and  oil. 

The  third  class  comprises  the  ALBUMENOID  or  nitrogenous  organic 
matters.  These  substances  derive  their  name  from  the  albumen  or 
white  of  an  egg,  which  was  among  the  earliest  to  be  studied,  and 
which  may  be  considered  as  a  representative  of  the  whole  class.  They 
differ  from  the  substances  of  the  two  preceding  groups,  especially  in  the 
fact  that  they  contain  nitrogen  as  an  ingredient,  in  addition  to  the 
three  elements  of  the  hydrocarbonaceous  matters.  They  are  exclu- 
sively of  organic  origin,  appearing  only  as  ingredients  of  the  living 
body.  Their  chemical  constitution  is  a  complicated  one — that  is,  their 
four  elements  are  united  in  such  a  way  as  to  form  compounds  of  a  very 
high  atomic  weight,  which  has  not,  however,  been  determined  with 
sufficient  precision  to  give  an  exact  chemical  formula.  Their  reactions 
with  other  substances  are  not  well  denned,  as  compared  with  the  inor- 
ganic constituents,  and  their  most  striking  physiological  properties  are 
not  such  as  can  be  expressed  in  chemical  phraseology.  Nevertheless, 
they  are  of  the  first  importance  as  ingredients  of  the  organized  frame, 
since  they  form  the  largest  portion  of  its  mass,  and  contribute  directly 
to  its  most  active  phenomena.  They  include  such  substances  as 
albumen,  caseine,  ptyaline,  pepsine,  and  myosine. 

The  fourth  class  is  composed  of  the  COLORING  MATTERS.  These  sub- 
stances, upon  which  the  different  tints  of  the  solids  and  fluids  depend, 
are  present,  for  the  most  part,  in  small  quantity,  the  most  abundant 
being  the  red  coloring  matter  of  the  blood. 

Lastly,  in  the  fifth  class  are  embraced  a  group  of  CRYSTALLIZABLE 
NITROGENOUS  MATTERS,  many,  if  not  all,  of  which  are  derived  from  the 
physiological  metamorphosis  of  albumenoid  substances.  They  are 
found  in  some  of  the  solid  tissues,  as  the  brain  and  nerves,  in  the  secre- 
tions of  the  liver,  and  especially  in  the  urine,  where  they  represent  the 
products  of  excretion. 


CHAPTER    II. 
INORGANIC  SUBSTANCES. 

THE  inorganic  substances  are  present  in  the  animal  body  in  great 
variety.  Some  of  them,  such  as  water  and  the  salts  of  lime,  con- 
stitute a  large  proportion  of  the  mass  of  the  tissues  and  fluids  in  which 
they  are  found ;  others  are  in  comparatively  small  quantity.  Some  of 
them  are  found  in  all  regions  of  the  body,  while  others  are  met  with 
only  in  particular  tissues  or  fluids ;  but  there  are  hardly  any  which  do 
not  appear  as  constituents  of  several  different  parts.  As  their  name 
implies,  these  substances  exist  abundantly  in  the  inorganic  world,  and 
form  a  large  part  of  the  crust  of  the  earth.  But  they  are  also  essential 
constituents  of  the  animal  frame,  and  necessary  ingredients  of  the 
food.  No  regimen  would  be  capable  of  supporting  life  indefinitely 
which  did  not  contain  them  in  due  proportion. 
This  group  includes  the  following  substances  : 

Water;  Potassium  phosphate; 

Sodium  chloride  ;  Potassium  sulphate  ; 

Sodium  phosphate  ;  Potassium  carbonate  ; 

Sodium  biphosphate ;  Lime  phosphate  ; 

Sodium  sulphate  ;  Lime  carbonate  ; 

Sodium  carbonate ;  Magnesium  phosphate  ; 

Potassium  chloride  ;  Magnesium  carbonate. 

Beside  the  substances  above  named  there  are  found,  as  constant  in- 
gredients of  the  incombustible  residue  of  various  parts  of  the  human 
body,  iron,  silica,  and  fluorine ;  but  it  is  not  certainly  known  in  what 
form  of  combination  these  substances  originally  existed  in  the  animal 
solids  and  fluids.  Sometimes,  but  not  always,  there  are  indications  of 
the  presence,  in  minute  quantity,  of  copper,  manganese,  and  lead,  also 
in  unknown  forms  of  combination. 

The  most  important  of  the  inorganic  substances,  considered  in  regard 
to  their  quantity  and  their  part  in  the  vital  phenomena,  are  the  fol- 
lowing : 

1.  Water,  H20. 

Water  is  present  in  all  the  tissues  and  fluids  of  the  body.  It  is 
abundant  in  the  blood  and  secretions,  where  it  is  indispensable  in  order 
to  give  them  the  fluidity  necessary  to  the  performance  of  their  functions. 
For  it  is  by  the  blood  and  secretions  that  new  substances  are  introduced 
into  the  body,  and  old  ingredients  discharged ;  and  it  is  a  necessary 
condition  both  of  the  introduction  and  discharge  of  solid  substances 

35 


36  PHYSIOLOGICAL    CHEMISTRY. 

that  they  assume,  for  the  time  being,  a  fluid  form.  Water  is  therefore 
an  essential  ingredient  of  the  animal  fluids,  for  it  holds  their  ingredients 
in  solution,  and  enables  them  to  pass  and  repass  through  the  animal 
frame. 

But  water  is  a  constituent  also  of  the  solids.  If  a  muscle  or  a  carti- 
lage be  exposed  to  gentle  heat  in  dry  air,  it  loses  water  by  evaporation, 
diminishes  in  bulk,  and  becomes  dense  and  stiff.  Even  the  bones  and 
teeth  lose  water  in  this  way,  though  in  smaller  quantity.  In  all  the 
solid  and  semi-solid  tissues,  the  water  which  they  contain  is  useful  by 
ii-iving  them  the  special  consistency  which  is  characteristic  of  them,  and 
which  would  be  lost  without  it.  Thus  a  tendon,  in  its  natural  condi- 
tion, is  white,  glistening,  and  opaque ;  and,  though  very  strong,  per- 
fectly flexible.  If  its  water  be  expelled  by  evaporation  it  becomes 
yellowish,  shrivelled,  semi-transparent,  inflexible,  and  unfit  for  perform- 
ing its  mechanical  functions.  The  same  is  true  of  the  skin,  the  muscles, 
the  cartilages,  and  the  glands. 

The  following  is  a  list,  compiled  by  Robin  and  Yerdeil  from  various 
observers,  showing  the  proportion  of  water  per  thousand  parts  in  dif- 
ferent solids  and  fluids : 

QUANTITY  OF  WATER  IN  1000  PAETS  IN 

Teeth      .        .        .        .100  Bile        .        .  .  .880 

Bones      .        .        .        .130  Milk       .        .  .  .887 

Cartilage.        .        .        .     550  Pancreatic  juice  .  .     900 

Muscles    .         .         .         .750  Urine      .         .  .  .936 

Ligaments        .         .         .     768  Lymph  ....     960 

Brain       ....     789  Gastric  juice  .  .  .     975 

Blood       .         .         .         .795  Perspiration  .  .  .986 

Synovial  fluid .         .        .805  Saliva    .        .  .  .995 

According  to  the  best  calculations,  water  constitutes,  in  the  human 
subject,  about  seventy  per  cent,  of  the  entire  bodily  weight. 

The  water  which  thus  forms  part  of  the  animal  frame  is  derived 
mainly  from  without.  It  is  taken  in  the  form  of  drink,  and  is  also 
abundant  in  various  kinds  of  food.  For  no  articles  of  food  are  taken  in 
an  absolutely  dry  state,  but  all  contain  more  or  less  water,  which  may 
be  expelled  by  evaporation.  The  quantity  of  water,  therefore,  daily 
taken  into  the  system,  cannot  be  ascertained  by  simply  measuring  the 
quantity  of  drink,  but  its  proportion  in  the  solid  food  must  also  be 
determined,  and  this  quantity  added  to  that  taken  in  with  the  fluids. 
By  measuring  the  fluid  taken  as  drink,  and  calculating  in  addition  its 
proportion  in  the  solid  food,  we  have  found,  in  accordance  with  the 
results  formerly  obtained  by  Barral,  that,  for  a  healthy  adult  man,  the 
average  quantity  of  water  introduced  into  the  system  is  about  2000 
grammes  per  day. 

There  is  reason  to  believe  that  a  certain  quantity  of  water  also  ni: 
its  appearance  within  the  body  by  the  liberation  of  its  elements  from 
various  organic  combinations.     This  is  shown  by  the  fact  that  a  con- 
siderable quantity  of  hydrogen  is  daily  introduced  into  the  system  in 


INORGANIC    SUBSTANCES.  37 

the  organic  ingredients  of  the  food,  which  is  not  wholly  accounted  for 
in  the  excretions.  The  most  reliable  estimates,  in  this  respect,  are  as 
follows : 

AVERAGE  DAILY  QUANTITY  OF  HYDEOGEN 

Introduced  in  organic  combinations  with  the  food       .         .         .40  grammes. 
Discharged     "                                              "      excretions      .         .6         " 
Kesidue  unaccounted  for 34         " 

Thus  not  more  than  fifteen  per  cent,  of  the  quantity  introduced  is 
discharged  in  the  organic  ingredients  of  the  excretions.  But  hydrogen 
is  not  exhaled  from  the  body  in  notable  quantity  in  a  free  state,  nor  in 
any  other  form  of  inorganic  combination  except  water.  The  intestinal 
gases  contain  habitually  hydrogen  and  carburetted  hydrogen  in  the 
proportion  of  about  thirty-eight  per  cent,  of  their  volume.*  The  abso- 
lute quantity  of  these  gases  in  the  normal  condition  has  not  been  deter- 
mined ;  but  it  is  evidently  quite  insufficient  to  account  for  the  missing 
hydrogen,  34  grammes  of  which  would  occupy,  in  the  gaseous  form,  a 
space  of  379  litres.  The  surplus  hydrogen  must  therefore  be  discharged 
in  the  form  of  water  or  watery  vapor.  The  estimates  given  above 
indicate  that  not  far  from  300  grammes  of  water  are  daily  produced  in 
the  body  in  this  way.  One  important  class  of  the  ingredients  of  the 
food,  hereafter  to  be  described,  already  contain  hydrogen  and  oxygen  in 
the  relative  quantities  necessary  to  form  water ;  and,  when  decomposed 
in  the  system,  they  may  readily  yield  these  elements  in  the  required 
proportions. 

Furthermore,  although  it  has  not  yet  been  proved,  in  any  particular 
case,  that  more  water  is  discharged  from  the  system  than  can  be 
accounted  for  by  that  introduced,  yet  a  comparison  of  the  average 
results  obtained  by  different  observers  always  tends  to  show  a  surplus 
of  water  discharged,  from  200  to  500  grammes  over  and  above  that  in- 
troduced with  the  food  and  drink.  The  quantity  of  water,  however, 
thus  produced  in  the  body  is  small  in  comparison  with  that  introduced 
and  discharged  under  its  own  form. 

While  in  the  interior  of  the  living  body,  water  is  useful  principally 
by  its  physical  properties.  It  is  the  universal  solvent  for  the  ingre- 
dients of  the  animal  fluids,  holding  them  in  solution  either  directly 
or  by  the  aid  of  other  substances  which  are  themselves  soluble.  It  thus 
enables  the  elements  of  the  food  to  find  their  way  into  the  circulating 
fluid,  and  into  substance  of  the  organs.  It  permeates  the  membranes 
and  brings  into  contact  with  each  other  the  inorganic  and  organic  mate- 
rials of  various  parts,  and  enables  them  to  assume  new  forms  by  mutual 
reaction.  In  this  way  it  is  subservient  to  the  phenomena  of  absorp- 
tion, transudation,  exhalation,  chemical  union  and  decomposition,  which 
make  up  the  nutritive  functions  of  the  animal  frame. 

*  Marchand :  Journal  fiir  praktische  Chemie.  Leipzig,  1848.  Band  XLIV.,  p.  10. 
Bilge:  Sitzungsberichte  der  Kaiserlichen  Akademie  der  Wissenschaften.  Wien, 
1862.  Band  XLIV.,  p.  739. 


PHYSIOLOGICAL    CHEMISTRY. 

After  forming  part  of  the  animal  solids  and  fluids,  and  taking  its 
share  in  the  vital  processes,  the  water  is  again  discharged;  for  its 
presence  in  the  body,  like  that  of  all  the  other  ingredients,  is  not  per- 
manent, but  temporary.  It  makes  its  exit  from  the  body  by  four 
different  passages,  namely,  as  a  liquid  in  the  urine  and  feces,  and  in 
the  form  of  vapor  by  the  lungs  and  skin.  The  quantity  expelled  in 
each  case  is  not  uniform,  but  varies  according  to  circumstances.  If 
the  kidneys  be  unusually  active,  the  watery  ingredients  of  the  urine 
are  increased  in  quantity,  while  the  cutaneous  perspiration  is  diminished ; 
and  the  state  of  the  atmosphere  and  the  rapidity  of  respiration  will 
influence  the  amount  of  watery  vapor  exhaled  by  the  lungs  and  skin. 
Still  there  is  a  well-marked  average  relation  between  the  activity  of  the 
various  organs  and  the  quantity  of  their  excreted  fluids.  It  appears 
from  a  comparison  of  the  researches  of  Lavoisier  and  Seguin,  Valentin, 
and  other  observers,  that  the  water  discharged  from  the  system  passes 
by  these  different  routes  nearly  in  the  following  proportions : 

By  exhalation  from  the  lungs       .....         20  per  cent. 

By  the  cutaneous  perspiration 30       " 

By  the  urine  and  feces 50       " 

While  only  four  per  cent,  of  the  water  is  expelled  with  the  feces, 
ninety-six  per  cent,  passes  out  by  the  lungs,  the  skin,  and  the  kidneys. 
It  is  evident,  therefore,  that  the  main  bulk  of  the  water  taken  in  with 
the  food  does  not  simply  pass  through  the  alimentary  canal,  but  enters 
the  circulation,  and  becomes  a  temporary  constituent  of  the  solid  tissues. 
As  it  appears  in  the  secretions  it  brings  with  it  various  ingredients 
absorbed  from  the  glandular  organs ;  and  when  finally  discharged  it  is 
mingled,  in  the  urine  and  feces  with  salts  and  excrementitious  matters, 
and  in  the  cutaneous  and  pulmonary  exhalations  with  animal  vapors 
and  odoriferous  material  of  various  kinds.  In  the  perspiration  it 
contains  mineral  sulphates  and  chlorides,  which  it  leaves  behind  on 
evaporation. 

2.  Lime  Phosphate,  2(PO4)Ca3. 

This  substance  exists  as  an  ingredient  in  all  the  animal  solids  and 
fluids.  So  far  as  regards  its  mass,  it  is,  next  to  water,  the  most  im- 
portant of  the  inorganic  constituents  of  the  body,  its  entire  quantity 
being  much  greater  than  that  of  any  other  mineral  salt.  For  though 
not  especially  abundant  in  the  fluids  and  the  softer  tissues,  it  forms 
more  than  one-half  the  substance  of  the  bones.  It  is  estimated  by 
Barral  that  the  osseous  tissues  constitute  6.4  per  cent,  of  the  entire 
mass  of  the  body ;  and  lime  phosphate  forms  on  the  average  from  57 
to  58  per  cent,  of  the  substance  of  the  bones.  This  would  give,  for 
a  man  weighing  65  kilogrammes,  or  143  pounds  avoirdupois,  2400 
grammes  of  calcareous  phosphate  in  the  whole  body.  Its  proportion 
in  various  tissues  and  fluids  of  the  human  system  is  as  follows : 


INORGANIC    SUBSTANCES.  39 

QUANTITY  OF  LIME  PHOSPHATE  IN  1000  PARTS  IN  THE 
Enamel  of  the  teeth         .     885  Milk      .        .        .        .2.72 

Dentine  .        .         .         .643  Blood    ....     0.30 

Bone       .         .         .         .576  Bile       ....     0.92 

Cartilage         ...      40  Urine    ....     0.75 

Notwithstanding  the  large  quantity  of  lime  phosphate  in  the  body  as 
a  whole,  it  is  evident,  from  the  preceding  list,  that  most  of  it  is  deposited 
in  the  solid  tissues ;  while  it  is  present  in  but  slender  proportion  in 
the  animal  fluids.  Of  these  fluids,  milk  alone  contains  lime  phosphate 
in  notable  quantity,  where  it  is  plainly  subservient  to  the  ossification 
of  the  growing  bones  of  the  infant,  by  whom  the  milk  is  used  as  food. 
In  the  circulating  fluids,  the  internal  secretions,  and  the  urine,  on  the 
other  hand,  the  calcareous  salt  is  in  small  amount.  Its  importance  in 
the  body  depends  mainly  upon  its  physical  property  of  imparting  rigidity 
to  the  solid  tissues,  rather  than  upon  its  active  qualities  in  the  phe- 
nomena of  nutrition. 

In  the  solid  tissues  it  is  associated  with  other  earthy  and  alkaline 
salts,  but  largely  preponderates  over  them  in  amount.  In  the  bones,  the 
quantity  of  lime  phosphate  is  from  five  to  six  times  greater  than  that  of 
all  the  other  mineral  ingredients  together. 

In  the  bones,  teeth,  and  cartilages,  lime  phosphate  exists  in  a  solid 
form ;  not  deposited  mechanically  as  a  granular  powder,  but  united 
with  the  animal  matter  of  the  tissues,  like  coloring  matter  in  colored 
glass,  the  union  of  the  two  forming  a  homogeneous  material.  It  is  not, 
on  the  other  hand,  so  combined  with  the  animal  matter  as  to  lose  its 
identity  and  constitute  a  new  substance,  as  where  hydrogen  combines 
with  oxygen  to  form  water  ;  but  rather  as  salt  unites  with  water  in  a 
saline  solution,  both  substances  retaining  their  original  character  and 
composition,  though  too  intimately  associated  to  be  separated  by 
mechanical  means.  The  lime  phosphate,  therefore,  may  be  extracted 
by  maceration  in  dilute  muriatic  acid,  leaving  behind  the  animal  sub- 
stance, which  still  retains  the  original  form  of  the  bone  or  cartilage. 

In  the  solid  tissues,  lime  phosphate  is  useful  by  giving  to  them 
their  due  consistence  and  solidity.  In  the  enamel  of  the  teeth,  the 
hardest  tissue  of  the  body,  it  predominates  exceedingly  over  the  ani- 
mal matter,  and  is  present  in  greater  proportion  than  in  any  other  part 
of  the  frame.  In  the  dentine  it  is  in  somewhat  smaller  quantity,  and 
in  the  bones  smaller  still ;  though  in  the  bones  it  continues  to  form 
more  than  one-half  their  entire  mass.  The  importance  of  this  sub- 
stance, in  communicating  to  bones  their  natural  stiffness  and  consist- 
ency, is  shown  by  the  alteration  which  they  suffer  from  its  removal. 
If  a  long  bone  be  macerated  in  dilute  muriatic  acid,  the  earthy  matter 
is  dissolved  out,  the  bone  loses  its  rigidity,  and  may  be  bent  or  twisted 
in  any  direction  without  breaking.  (Fig.  1.) 

In  the  formation  of  the  bony  skeleton  during  foetal  life,  infancy,  and 
childhood,  the  cartilaginous  substance  previously  existing  is  replaced 


PHYSIOLOGICAL    CHEMISTRY. 


FIG.  1. 


by  osseous  matter,  which  contains  a  larger  proportion  of  calcareous 
salts ;  while  the  anatomical  texture  of  the  parts  is  also  changed,  giving 
rise  to  the  characteristic  forms  of  bony  tissue.  This  progressive  con- 
solidation of  the  skeleton  is  known  as  the  process  of  "ossification." 
In  some  instances  it  is  defective,  owing  to  partial 
failure  in  the  powers  of  assimilation ;  and  as  the 
rigidity  of  the  skeleton  does  not  increase  in  propor- 
tion to  the  weight  of  the  body  and  the  force  of  mus- 
cular action,  the  bones  become  gradually  bent  and 
deformed,  sometimes  to  an  extraordinary  degree.  This 
affection  has  received  the  name  of  Eachitis. 

A  similar  result  is  produced  by  a  morbid  softening 
of  the  bones,  sometimes  occurring  in  adult  life,  known 
as  Osteomalakia.  In  this  disease  the  bony  fabric,  after 
its  formation,  becomes  altered  in  texture  and  compo- 
sition, and,  the  new  substance  which  takes  its  place 
being  deficient  in  calcareous  matter,  there  is  a  pro- 
gressive yielding  and  deformity  of  the  skeleton,  like 
that  which  happens  in  rachitis. 

In  the  plasma  of  the  blood  the  lime  phosphate, 
though  insoluble  in  alkaline  watery  liquids,  is  held  in 
solution  by  union  with  the  albuminous  ingredients. 
It  has  been  shown  by  Fokker  that  the  earthy  phos- 

FIBULA     TIED     IN    A      j^g      ^fcft    ^     ^j^     Qf  ^j^     with     ^     ^^ 

KNOT,    after    macera- r 

tion  in  a  dilute  acid,  mmous  matter  and  become  soluble  in  considerable 
From  a  specimen  pre-  proportion.  This  explains  the  presence  of  lime  phos- 
phate in  a  liquid  form  in  the  blood  and  in  the  milk, 
both  fluids  with  an  alkaline  reaction.  In  the  urine,  on  the  other  hand, 
it  is  held  in  solution  by  the  acid  sodium  biphosphate.  Accordingly, 
when  the  urine  is  rendered  alkaline  by  the  addition  of  soda  or  potassa, 
the  earthy  phosphates  are  precipitated,  forming  a  white  turbidity. 

The  source  of  the  lime  phosphate  of  the  animal  solids  and  fluids  is  in 
the  food.  It  exists  in  nearly  every  animal  and  vegetable  alimentary 
matter  in  common  use.  It  is  found  not  only  in  muscular  flesh,  eggs, 
and  milk,  and  in  all  the  cereal  grains,  as  wheat,  rye,  oats,  barley,  maize, 
and  rice,  but  also  in  peas  and  beans,  the  nutritive  tubers  and  roots,  as 
potatoes,  beets,  turnips,  and  carrots,  and  even  in  juicy  fruits,  such  as 
the  apple,  pear,  plum,  and  cherry. 

After  forming  for  a  time  a  constituent  part  of  the  body,  the  lime 
phosphate  is  discharged  with  the  excretions,  but  slowly  and  in  small 
amount.  According  to  the  observations  of  Neubauer  and  Beneke, 
about  0.4  gramme,  on  the  average,  is  daily  expelled  with  the  urine. 
A  slightly  larger  quantity  is  found  in  the  feces,  but  this  may  be  only 
a  residue  from  the  undigested  portion  of  the  food.  Only  traces  of  it 
are  to  be  detected  in  the  perspiration.  As  so  large  a  quantity  of  this 
salt,  therefore,  is  contained  in  the  body,  while  so  little  is  expelled 
daily  with  the  excretions,  it  is  evidently  one  of  the  more  permanent 


IN  ORGAN  1C    SUBSTANCES.  41 

constituents  of  the  frame ;  comparatively  inactive  in  the  process  of 
internal  metamorphosis,  and  serving  for  the  most  part  as  a  physical 
ingredient  of  the  solid  tissues. 

3.  Lime  Carbonate,  C03Ca. 

Lime  carbonate  is  found  in  the  bones,  the  teeth,  the  blood,  the 
lymph  and  chyle,  the  saliva,  and  sometimes  in  the  urine.  In  all  these 
situations  it  is  in  much  smaller  proportion  than  the  calcareous  phosphate 
with  which  it  is  associated.  In  the  bones,  however,  it  is  next  in  im- 
portance to  the  lime  phosphate,  being  on  the  average  one-seventh  as 
abundant  as  that  salt,  and  much  more  so  than  any  of  the  remaining 
mineral  ingredients.  In  the  animal  fluids,  its  solubility  is  accounted  for 
by  the  presence  of  the  alkaline  chlorides  or  by  that  of  free  carbonic  acid. 

4.  Magnesium  Phosphate,  2(PO4)Mg3. 

Magnesium  phosphate  was  formerly  associated  with  the  corresponding 
lime  salt,  under  the  name  of  the  earthy  phosphates,  owing  to  certain 
resemblances  in  their  chemical  relations.  Like  the  lime  phosphate, 
which  it  everywhere  accompanies,  though  for  the  most  part  in  smaller 
quantity,  it  is  present  in  all  the  tissues  and  fluids  of  the  body.  Thus 
in  the  bones  the  lime  phosphate  is  in  the  proportion  of  576  parts  per 
thousand,  while  the  magnesium  phosphate  forms  only  12.5  parts.  In 
the  blood,  the  calcareous  salt  amounts  to  0.30  part  per  thousand,  the 
magnesium  salt  to  0.22  part;  and  in  the  milk  there  are  2.72  parts  of 
lime  phosphate  to  0.53  part  of  magnesium  phosphate.  On  the  other 
hand,  the  salts  of  magnesium  have  been  found  in  larger  quantity  than 
those  of  lime  in  the  muscles,  and  nearly  twice  as  abundant  in  the  sub- 
stance of  the  brain. 

The  magnesium  phosphate  is  discharged,  by  the  urine,  in  the  average 
daily  quantity  of  0.6  gramme.  The  amount  of  both  the  earthy  phos- 
phates together  is  accordingly  about  1  gramme  per  day  ;  the  magnesian 
salt  being  rather  the  more  abundant  of  the  two. 

Both  the  magnesium  phosphate  and  carbonate,  of  which  latter  salt 
traces  occur  in  the  blood,  appear  to  have  similar  physiological  relations 
with  the  corresponding  salts  of  lime,  and  present  the  same  features  in 
their  union  with  the  tissues  and  their  solubility  in  the  animal  fluids. 

5.  Sodium  Chloride,  NaCl. 

This  is  undoubtedly  the  most  important  of  the  mineral  constituents 
of  the  body,  as  regards  its  general  distribution  and  its  active  part 
in  the  phenomena  of  nutrition.  It  is  the  most  abundant  of  all,  next 
to  lime  phosphate,  and  is  present  in  all  the  animal  tissues  and  fluids. 
Its  entire  quantity  in  the  human  body  is  estimated  by  Dr.  Lankester 
at  110  grammes,  or  nearly  one-quarter  of  a  pound  avoirdupois.  In 
the  blood  it  is  nearly  as  abundant  as  all  the  other  mineral  ingredients 
together.  Its  proportion  in  various  parts  of  the  body  is  as  follows : 


42  PHYSIOLOGICAL,    CHEMISTRY. 


OF    SoDIl'M    ClILOKIDE    IN    1000    PARTS    IN    THE 

Bones    ....  7.02  Saliva     .         .         .         .1.53 

Blood     ....  3.36  Milk        ....     0.30 

Bile        ....  3.18  Lymph   ....     5.00 

•  Gastric  juice          .         .  1.70  Sebaceous  mutter  .         .     5.00 

Perspiration  .         .  2/2-')  Urine      ....     5.50 

One  of  the  most  important  characters  of  this  salt  is  its  property  of 
regulating  the  phenomena  of  endosmosis  and  exosmosis,  or  the  tran- 
sudation  of  fluids  through  the  organic  membranes.  This  property 
is  shared  by  the  other  mineral  ingredients  of  the  blood,  but  is  more 
important  in  the  case  of  sodium  chloride,  owing  to  its  preponderance 
in  quantity  over  the  rest. 

As  sodium  chloride  is  present  in  all  parts  of  the  body,  it  is  also  an 
important  ingredient  of  the  food.  It  occurs  in  all  animal  food  as  a 
natural  ingredient  of  the  corresponding  tissues.  In  muscular  flr-h. 
however,  it  is  less  abundant  than  potassium  chloride,  while,  on  the  other 
hand,  it  is  more  abundant  in  the  blood.  It  exists  also  in  various  kinds 
of  vegetable  food. 

According  to  Boussingault,  it  is  found  in  the  following  proportions 
in  certain  vegetable  substances  : 

PROPORTION  OF  SODIUM  CHLORIDE  IN  1000  PARTS  IN 

Potatoes         .        .        .     0.43  Oats       .        .        .        .0.11 

Beets      ....     0.66  Peas       ....     0.09 

Turnips  ....     0.28  Beans    ....     0.00 

Cabbage         .        .        .     0.40  Meadow  hay  .        .        .    3.28 

The  relative  quantity  of  sodium  chloride  consumed  in  animal  and 
vegetable  food  has  not  been  determined.  In  regard  to  the  demand  for 
this  salt,  however,  there  is  a  striking  difference  between  the  carnivo- 
rous and  herbivorous  animals.  The  carnivora  receive  a  sufficient  sup- 
ply with  their  natural  food,  and  usually  show  a  repugnance  to  salt 
as  well  as  to  salted  meats.  On  the  other  hand,  the  horse  and  rumi- 
nating animals  have  an  instinctive  desire  for  salt.  They  greedily  devour 
it,  when  offered  to  them,  in  addition  to  that  naturally  contained  in  their 
food,  and  it  is  shown  by  common  experience  that  a  liberal  supply  of 
salt  is  important  for  their  healthy  nutrition. 

The  same  fact  has  been  demonstrated  in  a  more  exact  manner  by  the 
experiments  of  Boussingault.*  This  observer  made  a  series  of  com- 
parative investigations  upon  the  growth  of  two  sets  of  bullocks  of  the 
same  age  and  vigor,  and  supplied  equally  with  an  abundance  of  ordi- 
nary nutritious  food,  those  of  one  set  receiving  in  addition  each  34 
grammes  of  salt  per  day.  At  the  end  of  six  months  the  difference  in 
the  aspect  of  the  animals  of  the  two  sets  began  to  be  evident,  and 
became  more  marked  as  time  went  on.  The  experiment  lasted  for  a 
year,  and  at  the  end  of  that  time  both  sets  of  animals  had  equally 
increased  in  weight;  but  those  fed  with  ordinary  food  presented  a 

*  Chimie  Agricole.     Paris,  1854,  p.  251. 


INORGANIC    SUBSTANCES.  43 

rough  and  tangled  hide,  and  a  dull,  inexcitable  disposition,  while  in 
those  which  had  received  the  additional  ration  of  salt  the  hide  was 
smooth  and  glistening,  and  the  general  appearance  was  vigorous  and 
animated.  While  these  animals,  therefore,  may  subsist  for  a  time 
upon  the  salt  naturally  contained  in  their  food,  an  additional  quantity 
is  required  to  maintain  the  system  in  good  condition  for  an  indefinite 
period. 

There  is  a  similar  necessity  for  salt  as  an  addition  to  the  food  of  the 
human  species.  No  other  condiment  is  so  universally  employed ;  and 
its  use  seems  to  be  based  upon  an  instinctive  demand  of  the  system  for 
a  substance  which  is  necessary  for  the  full  performance  of  its  functions. 
Beside  other  properties,  it  no  doubt  acts  in  a  favorable  manner  by 
exciting  the  digestive  secretions,  and  by  assisting  in  this  way  the  solu- 
tion of  the  food.  Food  which  is  tasteless,  however  nutritious  in  other 
respects,  is  taken  with  reluctance  and  digested  with  difficulty ;  while 
the  attractive  flavor  developed  by  cooking,  and  by  the  addition  of 
salt  and  other  condiments,  excites  the  secretion  of  the  saliva  and  gastric 
juice,  and  thus  facilitates  digestion.  The  sodium  chloride  taken  with 
the  food  is  afterward  absorbed  from  the  intestine,  and  deposited  in 
various  quantities  in  different  parts  of  the  body. 

Notwithstanding  various  surmises  which  have  been  presented  as  to 
its  possible  decomposition  and  the  recombination  of  its  elements  in  the 
body,  we  have  no  certain  knowledge  of  such  changes  taking  place  in 
the  sodium  chloride  while  a  constituent  part  of  the  animal  frame.  It 
passes  from  the  alimentary  canal  to  the  blood,  from  the  blood  to  the 
tissues,  and  is  finally  discharged  with  the  urine,  mucus,  and  cutaneous 
perspiration  in  solution  in  these  fluids.  Under  ordinary  circumstances, 
much  the  largest  proportion  passes  out  by  .the  kidneys.  The  entire 
quantity  of  sodium  chloride  discharged  with  the  excretions  by  an  adult 
man  is  about  15  grammes  per  day  ;*  of  which  13  grammes  are  contained 
in  the  urine,  and  2  grammes  in  the  perspiration.  Thus,  of  all  the 
sodium  chloride  contained  in  the  body,  considerably  more  than  ten  per 
cent,  passes  through  the  system  in  twenty-four  hours.  This  plainly 
indicates  its  activity  and  importance  in  the  internal  changes  of  nu- 
trition. 

6.  Potassium  Chloride,  KC1. 

This  substance  is  found  in  many,  if  not  all,  of  the  animal  tissues 
and  fluids,  accompanying  the  sodium  chloride,  with  which  it  is  closely 
related  in  its  physiological  characters.  It  is  especially  abundant,  as 
compared  with  sodium  chloride,  in  the  muscles  and  in  the  milk,  less  so 
in  the  blood,  the  gastric  juice,  the  urine,  and  the  perspiration.  Both 
salts  are  neutral  in  reaction,  and  are  retained  in  the  liquid  form  in 
the  blood  and  secretions  by  solution  in  the  water  of  these  fluids. 
Potassium  chloride  is  introduced  as  an  ingredient  of  both  animal  and 

*  Neubaner  und  Vogel :  Analyse  des  Harns.  Wiesbaden,  1872,  p.  54.  Beneke : 
Pathologic  des  Stoffwechsels.  Berlin,  1874,  p.  322. 


44  PHYSIOLOGICAL    CHEMISTRY. 

vegetable  food,  and  is  discharged  with  the  mucus,  the  urine,  and  the 
perspiration. 

7.  Sodium  and  Potassium  Phosphates,  Xa2HPOt  and  K2HP04. 

These  substances,  associated  under  the  name  of  the  alkaline  phos- 
phates, are  of  great  importance  as  ingredients  of  the  animal  body. 
They  exist  in  all  its  solids  and  fluids,  and  in  the  latter  are  present  in 
the  liquid  form  by  means  of  their  ready  solubility  in  water.  They  are 
no  doubt  useful  in  a  variety  of  ways,  but  one  of  their  most  important 
characters  is  their  alkaline  reaction.  This  reaction  is  essential  to  a 
large  number  of  the  vital  processes,  and  is  present  in  all  the  animal 
fluids  contained  in  the  circulatory  system,  or  in  the  closed  cavities  of 
the  body.  An  acid  reaction,  on  the  other  hand,  belongs  to  but  few  of 
the  animal  fluids.  One  of  these  is  a  secretion  employed  in  the  digestive 
process ;  the  rest  are  all  discharged  externally. 

The  following  list  shows  the  comparative  frequency  of  alkaline  and 
acid  fluids  in  the  human  body : 

FLUIDS  WITH  AN  ALKALINE  REACTION.        FLUIDS  WITH  AN  ACID  REACTION. 

1.  Blood-plasma.  1.  Gastric  juice. 

2.  Lymph.  2.  Perspiration. 

3.  Aqueous  humor.  3.  Mucus  of  the  vagina. 

4.  Cephalo-rachidian  fluid.  4.  Urine. 

5.  Pericardial  fluid. 

6.  Synovia. 

7.  Fluids  of  the  living  muscular 

tissue. 

8.  Mucus  in  general. 

9.  Milk. 

10.  Spermatic  fluid. 

11.  Tears. 

12.  Saliva. 

13.  Bile. 

14.  Pancreatic  juice. 

15.  Intestinal  juice. 

If  we  take  into  account  the  carbonic  acid  exhaled  with  the  breath,  it 
is  evident  that  an  alkaline  condition  is  in  general  characteristic  of  the 
internal  fluids,  while  the  products  of  excretion  present  an  acid  reaction. 

Of  the  internal  fluids  the  most  essential  is  the  plasma  of  the  blood, 
since  it  supplies  the  materials  of  nutrition  to  the  entire  system  ;  and  its 
reaction  has  been  found  invariably  alkaline,  not  only  in  man,  but  also 
in  every  species  of  animal  in  which  it  has  been  examined.  This  reac- 
tion is  necessary  to  life,  since  Bernard  demonstrated  that  an  injection 
of  dilute  acetic  or  lactic  acid  into  the  veins  of  a  living  animal  produces 
death  even  before  the  point  of  neutralization  has  been  reached. 

The  alkaline  reaction  of  the  blood-plasma  gives  to  this  fluid  its 
capacity  for  dissolving  carbonic  acid.  According  to  Liebig,  water 
wli ich  holds  in  solution  one  per  cent,  of  sodium  phosphate  can  absorb 


j 


INORGANIC    SUBSTANCES.  45 

twice  its  usual  proportion  of  carbonic  acid ;  and  the  other  alkaline  salts 
have  a  similar  dissolving  action  upon  this  gas.  The  blood  as  it  circu- 
lates among  the  tissues  absorbs  from  them  the  carbonic  acid  formed  in 
their  substance,  and  carries  it  away  to  be  eliminated  by  the  lungs.  If 
this  important  property,  which  depends  upon  the  alkalescence  of  the 
blood,  be  lost  by  its  neutralization,  the  elimination  of  carbonic  acid  by 
the  lungs  is  no  longer  possible,  and  the  tissues  become  overloaded  by 
its  accumulation.  This  is  probably  the  cause  of  death  in  Bernard's 
experiment. 

The  alkalescence  of  the  blood-plasma  is  due  in  great  measure  to  the 
alkaline  phosphates,  which  are  present  in  human  blood  in  the  proportion 
of  0.67  per  thousand  parts.  A  peculiar  relation  exists  in  this  respect, 
for  different  classes  of  animals,  between  the  alkaline  phosphates  and  the 
alkaline  carbonates,  which  are  to  be  mentioned  hereafter.  Both  these 
groups  of  salts  have,  in  solution,  an  alkaline  reaction ;  and  both  con- 
tribute to  the  alkalescence  of  the  blood  in  man  and  animals.  But  in  the 
carnivorous  animals  it  is  the  phosphates  which  preponderate,  while  in 
the  herbivora  the  carbonates  are  more  abundant.  In  species  fed  upon 
both  animal  and  vegetable  food  the  two  kinds  of  salts  are  present  in 
nearly  equal  proportion  ;  and  in  the  same  animal  either  the  phosphates 
or  the  carbonates  may  be  made  to  predominate  by  increasing  the  pro- 
portion of  animal  or  vegetable  food  respectively.  This  is  due  to  the 
fact  that  muscular  flesh  is  comparatively  abundant  in  phosphates,  while 
vegetable  matters  abound  in  salts  of  the  organic  acids,  which  give  rise 
by  their  decomposition  in  the  system  to  carbonates  of  the  same  bases. 

The  alkaline  phosphates  are  mainly  derived  from  the  food.  They 
circulate  with  the  animal  fluids,  and  are  finally  excreted  under  their  own 
form  in  the  perspiration,  the  mucus,  and  the  urine.  A  partial  exception 
to  this  rule  is  found  in  the  urine,  where  a  portion  of  the  alkaline  sodium 
phosphate  is  replaced  by  the  acid  biphosphate,  giving  to  the  whole  fluid 
an  acid  reaction.  The  explanation  of  this  change,  as  generally  under- 
stood, is  the  following.  A  nitrogenous  organic  acid  of  new  formation, 
namely,  uric  acid,  makes  its  appearance  in  the  system,  and  is  excreted 
by  the  urine,  in  the  form  of  a  neutral  combination,  as  sodium  urate. 
It  is  believed  to  combine,  at  the  time  of  its  formation,  with  a  portion 
of  the  sodium  of  the  sodium  phosphate,  and  the  remainder  of  this  salt 
is  thus  converted  into  a  biphosphate.  The  normal  reaction  of  the  urine 
is  therefore  really  due  to  the  formation  in  the  body  of  an  acid  substance ; 
although  the  substance  so  produced  does  not  appear  in  the  urine  as  the 
immediate  cause  of  its  acidity. 

There  is  also  evidence  that  a  certain  amount  of  phosphoric  acid  is 
formed  in  the  body  by  the  process  of  oxidation.  A  substance  containing 
phosphorus  in  organic  combination,  known  as  "lecithine,"  exists  in 
various  parts  of  the  system,  especially  in  the  blood,  brain,  and  nerves, 
and  is  also  taken  with  certain  kinds  of  food ;  but  no  such  substance  is 
met  with  in  the  excreted  fluids,  where  phosphorus  exists  only  in  the 
form  of  the  phosphatic  salts.  It  is  no  doubt  oxidized  in  the  internal 


46  PHYSIOLOGICAL    CHEMISTRY. 

transformation  of  the  organic  substances,  thus  becoming  phosphoric 
acid,  which  in  turn  unites  with  the  alkaline  bases  to  form  phosphates. 
In  this  way  some  of  the  superabundant  acid  is  produced,  which  gives 
rise  to  the  reaction  of  the  excreted  fluids. 

The  sodium  and  potassium  phosphates,  including  the  acid  biphosphate, 
are  discharged  with  the  urine  to  the  amount  of  about  4.5  grammes  per 
day. 

8.  Sodium  and  Potassium  Carbonates,  C03Na2  and  C03K2. 

The  alkaline  carbonates,  as  mentioned  above,  are  associated  with  the 
phosphates  in  all  the  more  important  fluids  of  the  body.  They  are 
readily  soluble  in  watery  fluids,  and  assist  in  producing  the  alkalescence 
of  the  blood  and  secretions.  They  are  partly  introduced  with  the  food, 
where  they  exist  in  limited  quantity,  but  they  are  formed  in  great 
measure  within  the  body  by  the  decomposition  of  other  salts  of  vege- 
table origin.  Certain  fruits  and  vegetables,  such  as  apples,  cherries, 
grapes,  potatoes,  carrots,  and  the  like,  contain  malates,  tartrates,  and 
citrates  of  the  alkaline  bases.  It  has  been  often  observed  that  after  the 
use  of  fruits  and  vegetables  containing  the  above  salts,  the  urine  be- 
comes alkaline  from  the  presence  of  the  carbonates.  Lehmann  found, 
by  experiments  upon  his  own  person,  that  within  thirteen  minutes 
after  taking  15.5  grammes  of  sodium  lactate,  the  urine  had  an  alkaline 
reaction.  He  also  observed  that  a  solution  of  this  substance  injected 
into  the  jugular  vein  of  a  dog,  caused  the  urine  to  become  alkaline  at 
the  end  of  from  five  to  twelve  minutes.  The  conversion  of  these  salts 
into  carbonates  takes  place,  therefore,  not  in  the  intestine,  but  in  the 
blood.  The  same  observer  found  that,  in  many  persons  living  on  a 
mixed  diet,  the  urine  became  alkaline  in  two  or  three  hours  after  swal- 
lowing 0.65  gramme  of  sodium  acetate. 

The  organic  acid  in  these  cases  is  decomposed ;  and  the  original  salts 
are  thus  replaced  by  the  alkaline  carbonates,  which  appear  in  the  urine 
and  modify  its  reaction  as  above  described. 

A  preponderance  of  vegetable  food,  accordingly,  influences  the  quan- 
tity of  the  alkaline  carbonates  in  the  system,  and  consequently  the  reac- 
tion of  the  excretions.  As  a  rule,  the  urine  of  man  and  of  the  carnivo- 
rous animals  is  clear  and  acid,  while  that  of  the  herbivora  is  alkaline 
and  turbid  with  calcareous  deposits.  Such  turbid  and  alkaline  urine 
will  often  effervesce  with  acids,  showing  the  presence  of  carbonates  in 
considerable  quantity.  This  difference  depends  upon  the  alimentation 
of  the  animal,  and  although  in  carnivorous  and  herbivorous  animals 
under  ordinary  conditions  the  urine  is  respectively  acid  and  alkaline, 
if  they  be  both  deprived  of  food  for  a  few  days  the  urine  becomes  acid 
in  both,  since  they  are  then,  in  each  instance,  living  upon  their  own 
tissues.  Furthermore,  a  rabbit,  whose  urine  is  turbid  and  alkaline 
while  feeding  on  fresh  vegetables,  if  kept  on  a  diet  of  animal  food, 
soon  produces  an  excretion  which  is  clear  and  acid.  The  reverse  effect 
is  produced  upon  a  dog  by  changing  his  food  from  meat  to  vegetable 


INORGANIC    SUBSTANCES.  47 

matters.  Finally,  the  urine  of  the  young  calf  while  living  on  the  milk 
of  the  mother  is  clear  and  acid ;  but  after  the  animal  has  been  weaned 
and  feeds  upon  vegetable  matter,  its  urine  becomes  alkaline  and  turbid, 
like  that  of  the  adult  animal. 

9.  Sodium  and  Potassium  Sulphates,  S04Na2  and  S04K2. 

The  sulphates  are  constant  ingredients  of  the  body,  and  are  found  in 
several  of  the  animal  fluids,  including  the  blood,  the  lymph,  the  aqueous 
humor,  milk,  saliva,  mucus,  the  perspiration,  and  the  urine.  They  are 
usually,  however,  in  small  quantity,  as  compared  with  other  saline  mat- 
ters. In  the  blood  and  the  lymph  they  are  much  less  abundant  than 
either  the  chlorides,  phosphates,  or  carbonates.  In  the  milk  and  the 
saliva  there  is  hardly  more  than  a  trace  of  them ;  and  they  have  not 
been  found  in  the  bones,  the  gastric  juice,  the  bile,  or  the  pancreatic 
juice.  They  are  most  abundant  in  the  urine,  where  they  amount  to 
rather  more  than  one-half  the  quantity  of  the  phosphates,  and  they  are 
found  also,  in  small  proportion,  in  the  feces. 

The  sulphates  are  introduced  into  the  body,  to  some  extent,  with  the 
food  and  drink.  They  are  present,  in  minute  quantity,  in  muscular 
flesh  and  in  the  yolk  of  egg.  They  exist  also  in  certain  vegetable  pro- 
ducts, such  as  the  cereal  grains,  fruits,  and  tuberous  roots,  where  they 
are  less  abundant  than  the  phosphates,  though  often  more  so  than  the 
chlorides.  Spring  and  river  water,  used  for  drink,  usually  contains  sul- 
phates, including  sulphate  of  lime,  varying  in  amount,  according  to 
Payen,  from  .003  to  .06  per  thousand  parts.  In  the  water  of  the  Croton 
river,  with  which  the  city  of  New  York  is  supplied,  they  amount,  as 
shown  by  Prof.  Chandler,  to  a  little  more  than  .007  per  thousand  parts. 

Beside  the  sulphates  introduced  with  the  food  and  drink,  a  certain 
amount  of  sulphuric  acid  originates  within  the  body  by  oxidation,  in  a 
mode  analogous  to  that  already  described  for  phosphoric  acid.  The 
albuminous  substances,  which  form  so  important  a  part  of  the  solid  food, 
contain  sulphur  as  one  of  their  constituent  elements,  and  a  considerable 
quantity  is  accordingly  introduced  into  the  systenrin  the  form  of  organic 
combination.  The  entire  quantity  of  sulphur,  thus  forming  part  of  the 
organic  matters  of  the  human  body,  amounts,  according  to  Payen,*  to 
about  110  grammes;  and  at  least  1  gramme  is  taken  daily  with  the 
albuminous  ingredients  of  the  food.  A  portion  is  expelled  with  the 
daily  exfoliation  of  the  hair,  nails,  and  epidermis ;  but  no  such  sulphur- 
ous organic  compound  is  discharged  by  the  urine  and  feces  except  in 
insignificant  quantity.  On  the  other  hand,  the  sulphates  are  compar- 
atively abundant  in  the  excretions.  While  they  are  to  be  found  in  the 
blood  only  in  the  proportion  of  0.28  per  thousand,  they  exist  in  the 
urine  in  the  proportion  of  from  3.00  to  7.00  parts  per  thousand,  and  are 
discharged  by  this  channel  to  the  amount  of  about  4  grammes  per  day. 

These  facts  indicate  that  a  notable  quantity  of  sulphuric  acid  is  formed 

*  Substances  Aliinentaires.     Paris,  1865,  p.  68. 


48  PHYSIOLOGICAL    CHEMISTRY. 

in  the  body,  during  the  decomposition  of  albuminous  matters,  by  oxi- 
dation of  their  sulphur.  This  is  confirmed  by  the  fact  that  the  quantity 
of  sulphuric  acid  in  the  sulphates  eliminated  by  the  kidneys  is  increased 
by  a  flesh  diet,  and  also  by  the  administration  of  sulphur  or  a  sulphuret.* 
Dr.  Parkes  estimates  the  quantity  of  sulphuric  acid  thus  produced  in 
the  system  as  about  double  that  taken  in  the  form  of  sulphates  with  the 
food  and  drink.  It  unites  with  the  alkaline  bases,  displacing  the  weaker 
acids  with  which  they  were  combined,  and  thus  contributes  indirectly 
to  the  general  acid  reaction  of  the  excreted  fluids. 

The  foregoing  substances  are  the  most  important  of  the  inorganic 
ingredients  of  the  body.  They  are  distinguished  from  the  organic  in- 
gredients by  their  comparatively  simple  chemical  composition,  by  their 
external  origin,  and  by  the  part  which  they  take  in  the  constitution  and 
nourishment  of  the  animal  frame.  They  are  derived  for  the  most  part 
from  without,  being  taken  directly  from  the  materials  of  the  inorganic 
world.  There  are  some  exceptions  to  this  rule ;  as  in  the  case  of  the 
alkaline  carbonates  formed  in  the  body  by  decomposition  of  the  salts 
of  the  vegetable  acids ;  of  the  sodium  biphosphate  produced  from  the 
neutral  phosphate  by  the  action  of  an  organic  acid,  and  of  the  phos- 
phates and  sulphates  formed  by  the  process  of  oxidation.  But  the 
greater  part  of  the  substances  belonging  to  this  class  are  introduced 
with  the  food,  and  absorbed  by  the  animal  tissues  and  fluids,  in  the 
form  under  which  they  exist  in  external  nature.  The  lime  carbonate 
of  the  bones,  and  the  sodium  chloride  of  the  blood  and  the  tissues,  are 
the  same  substances  as  those  met  with  in  calcareous  rocks,  or  in  sea 
water. 

In  the  process  of  internal  nutrition  they  are  exempt,  as  a  general  rule, 
from  chemical  change.  Some  of  them,  such  as  the  lime  and  magne- 
sium phosphates,  are  mostly  deposited  in  the  solid  parts,  and  are  re- 
newed but  slowly,  contributing  mainly  to  the  physical  properties  of  the 
tissues,  and  taking  a  comparatively  small  share  in  the  actions  of  repair 
and  waste.  Others,  such  as  water  and  the  alkaline  chlorides,  are  intro- 
duced and  discharged-in  abundance,  passing  rapidly  through  the  system, 
and  playing  an  important  part  in  the  phenomena  of  solution  and  tran- 
sudation.  Others,  such  as  the  alkaline  phosphates  and  sulphates,  when 
formed  in  the  body  by  oxidation,  appear  in  the  urine  as  a  residue  from 
the  decomposition  of  other  substances. 

The  larger  proportion,  however,  of  the  inorganic  matters  are  reab- 
sorbed  from  the  tissues  in  which  they  were  deposited,  and  discharged 
unchanged  with  the  excretions.  They  do  not,  for  the  most  part,  par- 
ticipate directly  in  the  chemical  phenomena  of  the  living  bcdy  ;  but 
rather  serve  to  facilitate,  by  their  presence,  the  necessary  changes  of 
nutrition  in  other  ingredients  of  the  animal  frame. 

*  Neubauer  und  Vogel :  Analyse  des  Hums.     Wiesbaden,  187:2,  pp.  356,  357. 


CHAPTER    III. 
HYDEOCAEEONACEOUS   SUBSTANCES. 

rPHE  members  of  this  class  are  distinguished  from  the  preceding-  by 
-L  their  organic  origin.  They  appear  as  products  of  the  nutritive  actions 
of  organized  beings,  and  are  not  introduced  ready  formed  from  the  in- 
organic world.  They  exist  both  in  vegetables  and  in  animals.  In  the 
former  they  are  produced  as  new  combinations,  under  the  influence  of 
the  vegetative  process ;  and  even  in  animals,  which  feed  upon  vegeta- 
bles or  upon  other  animals,  they  are  so  modified  by  digestion  and 
assimilation  that  they  present  themselves,  as  final  constituents  of  the 
body,  under  new  and  specific  forms.  They  all  consist  of  carbon,  hydro- 
gen, and  oxygen,  of  which  carbon  is  present  by  weight  in  especially 
large  proportion,  forming  from  44  to  84  per  cent,  of  the  entire  sub- 
stance. Owing  to  the  absence  of  nitrogen,  which  is  an  important  ele- 
ment in  organic  matters  of  the  following  class,  they  are  known  as 
"  non-nitrogenous  "  substances.  They  are  divided  into  two  principal 
groups,  namely :  the  carbo-hydrates,  or  substances  containing  carbon, 
with  hydrogen  and  oxygen  in  the  proportions  to  form  water ;  and  the 
fatty  matters,  in  which  the  proportions  of  carbon  and  hydrogen  are 

Increased,  while  that  of  oxygen  is  diminished.     The  group  of  the  carbo- 
lydrates  includes  starch,  glycogen,  and  sugar. 
J 


Starch,  C6H1005. 

A   special  physiological   interest   attaches  to   starch  from  the  fact 
hat  it  is  the  first  organic  substance  produced,  in  vegetation,  from  inor- 
ganic  materials.     The   animal  body  is  incapable  of  forming  organic 
matter,  and  must  be  supplied  with  these  substances  in  the  food.     But 
vegetables  have  the  power  of  combining  inorganic  elements  in  such  a 

!way  as  to  produce  a  new  class  of  bodies,  peculiar  to  the  organic  world, 
and  capable  of  serving  for  nutrition.  This  is  shown  by  numerous  ex- 
periments, in  which  seeds  or  young  plants,  artificially  cultivated  in  a 
soil  of  clean  sand,  moistened  only  with  solutions  of  mineral  salts,  have 
germinated,  grown,  and  fructified,  increasing,  many  times  over,  the 
quantity  of  organic  material  which  they  contained  at  the  beginning. 

This  production  of  organic  matter  takes  place  in  the  leaves  and  other 
green  tissues  of  growing  plants,  under  the  influence  of  the  solar  light ; 
and  the  first  substance  which  makes  its  appearance  under  these  condi- 
tions is  nearly  always  starch.  It  is  produced  from  two  inorganic  mat- 
ters absorbed  from  without,  namely,  carbonic  acid  and  water,  which  are 
deoxidized  by  the  vegetable  tissues,  and  their  elements  combined  to 
form  a  carbo-hydrate.  This  is  proved  by  the  fact  that  oxygen  is  ex- 

D  49 


50  PHYSIOLOGICAL    CHEMISTRY. 

haled,  during  the  vegetative  process,  in  the  same,  or  nearly  the  same, 
proportion  as  that  in  which  it  originally  existed  in  the  carbonic  acid; 
and  the  new  substance  produced  contains  hydrogen  and  oxygen  in  the 
proportions  to  form  water.  The  production  of  starch  in  growing  veg- 
etables is  therefore  represented  by  the  following  formula : 

CARBONIC  ACID.     WATER.  STARCH. 

600,     +     5  H2  O       -    012     =    C6  H10  05. 

The  production  of  starch  in  this  way  by  vegetation  is  a  phenomenon 
of  the  first  importance  in  the  economy  of  living  beings.  It  is  the  only 
natural  process  known  to  take  place  on  the  earth  by  which  oxygen  is 
set  free  from  its  actual  combinations.  It  is  a  reduction  of  two  com- 
pounds in  which  the  oxygen  affinity  of  carbon  and  hydrogen  was  fully 
satisfied,  resulting  in  the  formation  of  an  organic  matter  capable  of 
reoxidation.  The  new  substance  so  produced  has  therefore  a  power 
of  combination,  which  may  be  afterward  brought  into  activity  under 
requisite  conditions,  and  which  is  the  theoretical  basis  of  all  force  mani- 
fested by  the  living  organism. 

There  are  two  conditions  requisite  for  the  formation  of  organic  mat- 
ter by  vegetable  tissues:  First,  the  access  of  solar  light,  either  by 
direct  sunshine  or  by  diffused  daylight,  and,  secondly,  the  existence  in 
the  living  plant  of  the  green  coloring  matter  known  as  "  chlorophylle." 
Green  vegetables,  which  absorb  carbonic  acid  and  exhale  oxygen  in  the 
sunshine,  cease  to  do  so  when  daylight  disappears,  and  remain  inactive 
in  this  respect  during  the  night.  On  the  other  hand,  colorless  vege- 
tables, and  the  uncolored  portions  of  green  plants,  have  no  reducing 
action,  even  in  the  daytime. 

The  materials  for  this  reduction  process  in  vegetables,  namely,  car- 
bonic acid  and  water,  are  supplied  from  the  atmosphere  and  the  soil. 
As  the  atmosphere  contains  about  .05  per  cent,  of  its  volume  of  carbonic 
acid,  and  as  the  column  of  air  above  each  square  metre  of  surface,  at  the 
ordinary  barometric  pressure,  weighs  a  little  over  10,000  kilogrammes, 
this  would  give,  by  weight,  7.5  kilogrammes  of  carbonic  acid  to  the 
square  metre,  equivalent  to  30,390  kilogrammes,  or  rather  more  than 
thirty  tons,  over  each  acre  of  land.  From  this  abundant  reserve,  the 
carbonic  acid  is  supplied  for  vegetation.  It  is  absorbed  directly  by  the 
foliage  in  contact  with  the  atmosphere,  and,  brought  down  in  solution 
by  the  rain,  it  is  taken  up  by  the  roots  and  transferred  to  the  leaves 
by  the  vegetable  juices.  The  activity  of  the  reducing  process  has  been 
measured  by  Boussingault.*  He  found  that  a  single  fresh  oleander  leaf 
in  sunshine  decomposed  in  two  successive  days  nearly  49  cubic  centi- 
metres of  carbonic  acid;  and,  as  a  mean  of  six  similar  experiments, 
each  square  centimetre  of  leaf  surface  decomposed  1.33  cubic  centi- 
metres of  the  gas,  exhaling  an  equal  volume  of  free  oxygen.  It  is 
estimated  by  Hoppe-Seyler,  that,  considering  the  amount  of  oxygen 
consumed  by  animal  organisms  and  the  time  during  which  these  organ- 

*  Comptfs  reiulus  do  rAfiult-mk'  cles  Sciences,  Paris.     Tome  LXI.,  pp.  4(J8,  502. 


HYDROCARBONACEOUS  SUBSTANCES. 


51 


FIG.  2. 


GRAINS  OF  POTATO  STARCH. 


isms  have  existed  upon  the  earth,  the  whole  of  the  free  oxygen  now 
present  in  the  atmosphere  must  have  once  been  liberated  from  its  com- 
binations by  the  vegetative  process. 

When  first  produced  in  the  vegetable  tissue,  starch  is  in  the  form 
of  minute,  rounded,  homogeneous  granules.  These  granules  after- 
ward increase  in  bulk,  reaching 
a  size  which  varies  in  differ- 
ent instances  from  2.5  to  50  or 
60  mmm*  in  diameter.  They 
often  acquire  a  definite  struc- 
ture, each  granule  exhibiting 
under  the  microscope  a  series 
of  layers  or  concentric  markings, 
arranged  round  a  single  point, 
like  the  scar  of  a  ripe  seed, 
which  is  termed  the  "hilum." 
These  characters  differ  more  or 
less,  according  to  the  period  of 
growth  of  the  starch  granule 
and  the  tissue  from  which  it 
is  derived ;  but  they  are  suffi- 
ciently well  marked  in  nearly 
all  the  varieties  which  are  pre- 
pared for  food  or  employed  in  the  arts.  The  starch  grains  of  the  potato 
are  among  the  most  characteristic. 

The  successive  layers  of  which  starch  granules  are  composed  differ 
mainly  in  their  consistency,  being  alternately  harder  and  softer,  thus 
producing  a  corresponding  difference  in  refractive  power,  and  an  appear- 
ance of  concentric  striation.  Each  granule,  furthermore,  consists  of 
two  substances,  intimately  mingled  in  every  part  of  its  mass,  which 
resemble  each  other  completely  in  chemical  composition,  but  differ  in 
solubility.  These  substances  are,  first,  granulose,  which  may  be  ex- 
tracted from  the  starch  grain  by  boiling  water ;  and,  second,  cellulose, 
which  remains  undissolved.  The  granulose  is  usually  much  the  more 
abundant  of  the  two,  but  the  cellulose  has  so  marked  a  consistency 
that  it  retains  the  form  and  laminated  appearance  of  the  starch  grain, 
after  extraction  of  the  granulose,  though  reduced  to  five  or  six  per 
cent,  of  its  original  weight. 

As  starch  is  the  earliest  and  simplest  product  of  vegetation,  it  is  most 
abundantly  diffused  through  the  vegetable  kingdom,  and  exists,  for  at 
least  a  certain  period,  in  every  plant  which  has  yet  been  examined  for 
it.  It  occurs  especially  in  seeds,  in  the  cotyledons  of  the  young  plant, 
in  roots,  tubers,  and  bulbs,  in  the  pith  of  stems,  and  sometimes  in  the 
bark.  It  is  very  abundant  in  corn,  wheat,  rye,  oats,  and  rice,  in  the 

*  The  sign  mmm.  stands  for  micro-millimetre ;  that  is,  the  one-thousandth  part  of  a 
millimetre.  A  millimetre  is  very  nearly  equivalent  to  one  twenty-fifth  of  an  inch ; 
and  a  micro-millimetre,  accordingly,  is  about  23^00  of  an  inch. 


52  PHYSIOLOGICAL    CHEMISTRY. 

potato,  in  peas  and  beans,  and  in  most  vegetable  substances  used  as 
food.  It  constitutes  almost  entirely  the  preparations  known  as  sago, 
tapioca,  arrow-root,  and  maizena,  which  are  nothing  more  than  varie- 
ties of  starch,  extracted  from  different  plants. 

The  following  list,  compiled  mainly  from  the  tables  of  Payen,*  shows 
the  percentage  of  starch  in  various  kinds  of  food : 

QUANTITY  OF  STARCH  IN  100  PARTS  IN 

Wheat  ....  57.88  Potatoes      .  .  .  20.00 

Rye       ....  64.65  Sweet  potatoes  .  .  16.05 

Oats      ....  60.59  Peas    ....  37.30 

Barley  ....  66.43  Beans.         .  .  .  33.00 

.     Indian  com   .         .         .  67.55  Flaxseed      .  .  .  23.40 

Rice      ....  88.65  Chocolate  nut  .  .  11.00 

Starch  derived  from  all  these  sources  has  essentially  the  same  chemi- 
cal composition,  and  may  be  recognized  by  the  same  tests.  It  is  in- 
soluble in  cold  water,  but  if  treated  with  about  twenty  times  its  weight 
of  boiling  water  its  granules  swell,  become  gelatinous  and  amorphous, 
combine  with  a  certain  proportion  of  water,  and  fuse  into  an  opaline 
liquid,  which  is  thicker  or  thinner  according  to  the  quantity  of  water 
present,  and  which  solidifies,  on  cooling,  into  a  nearly  homogeneous 
paste,  the  water  remaining  united  with  the  amylaceous  matter.  The 
starch  is  then  in  a  pasty  and  amorphous  condition,  its  chemical  proper- 
ties remaining  essentially  unaltered.  If  treated  with  100  or  150 
parts  of  water  at  the  boiling  temperature  it  makes  a  liquid  which  does 
not  gelatinize  on  cooling ;  but  the  imperfectly  liquefied  portions,  con- 
taining the  insoluble  cellulose,  gradually  subside  as  a  turbid  deposit, 
while  the  soluble  starch  remains  above,  forming  a  clear  and  colorless 
liquid. 

Starch  is  especially  distinguished  by  its  property  of  striking  a  blue 
color  with  iodine.  This  reaction  will  take  place  even  with  raw  starch, 
and  its  granules  may  be  recognized  under  the  microscope  by  this 
means.  It  is  still  more  prompt  when  the  starch  has  been  boiled  to  a 
paste,  and  especially  when  it  is  in  solution.  A  minute  quantity  of  tinc- 
ture of  iodine,  added  to  a  starch  solution,  produces  at  once  a  deep  blue 
color,  which  may  be  largely  diluted  without  losing  its  characteristic 
tinge.  This  test,  however,  must  be  employed  at  a  moderate  tempera- 
ture. If  the  solution  be  too  hot,  no  visible  reaction  will  occur ;  and 
even  after  it  has  taken  place,  if  heat  be  applied  the  blue  color  will  dis- 
appear, to  return  again  after  cooling  down  to  the  proper  temperature. 
The  iodine  must  also  be  used  in  a  free  state.  If  added  in  the  form  of 
a  soluble  iodide  it  will  produce  no  effect,  since  the  starch  has  not  suf- 
ficient affinity  to  withdraw  it  from  its  union  with  other  matters. 
Finally,  no  third  substance  must  be  present  which  would  be  capable  of 
combining  with  the  iodine  and  thus  preventing  its  action  on  starch. 
Many  animal  fluids,  such  as  the  serum  of  blood,  saliva,  mucus,  and  urine, 

*  Substances  Aliinentaires.     Paris,  1805. 


HYDROCARBONACEOUS    SUBSTANCES.  53 

contain  ingredients  which  interfere  with  the  reaction,  and  may  even 
dissipate  the  blue  color  after  it  has  been  produced.  These  substances 
must  be  removed  before  the  application  of  the  test,  or  the  iodine  must 
be  added  in  excess  to  allow  for  action  on  the  starch.  With  these  pre- 
cautions it  forms  a  valuable  test. 

Starch  has  the  property  of  being  changed,  under  certain  conditions, 
into  two  other  substances. 

1.  If  subjected  to  torrefaction,  that  is,  a  dry  heat  of  210°  C.  (about 
400°  F.),  it  is  converted  into  Dextrine,  a  gummy  substance  soluble  in 
water,  so  called  from  the  fact  that  in  solution  it  rotates  the  plane  of  the 
polarized  ray  toward  the  right.*    Dextrine  has  the  same  chemical  com- 
position with  starch,  but  its  physical  properties  are  different,  and  when 
treated  with  iodine  it  takes  a  rosy  red  instead  of  a  blue  color.     The 
same  transformation  of  starch  is  accomplished  by  boiling  with  a  dilute 
acid;  the  solution  becoming  in  a  few  minutes  clear  and  liquid,  and 
changing   its   reaction  with  iodine.     Finally,  in  the   germination  of 
certain  starchy  seeds,  such  as  the  cereal  grains,  the  transformation  of 
starch  into  soluble  dextrine  takes  place  in  the  presence  of  moisture  at 
moderate  temperatures,  under  the  influence  of  a  nitrogenous  ferment. 

2.  Starch  may  be  converted  into  Sugar.     When  a  starch  solution  or 
thin  starch  paste  is  boiled  with  a  dilute  acid,  it  is  first  changed,  as  de- 
scribed above,  into  dextrine.     But  by  continued  boiling  for  several 
hours  it  begins  to  be  further  transformed  into  sugar,  and  at  last  it  passes 
wholly  into  the  saccharine  condition.    The  same  conversion  takes  place 
during  the  germination  and  growth  of  plants,  where  sugar  makes  its 
appearance  at  the  expense  of  the  starch,  as  soon  as  the  requisite  moist- 
ure and  warmth  are  supplied.     This  is  the  usual  source  of  sugar  in 
vegetable  juices,  the  starch  previously  stored  up  being  changed  into 
sugar  by  the  molecular  actions  going  on  in  the  vegetable  fabric.    Finally, 
various  nitrogenous  animal  substances,  like  those  in  the  saliva  or  the 
intestinal  juices,  at  the  temperature  of  38°  C.,  have  the  same  effect. 
This   is   the   change   which   normally  takes   place   during  digestion. 
Starchy  substances,  when  taken  as  food,  are  changed  into  sugar  in 

*  A  ray  of  light  which  has  passed  through  certain  crystalline  bodies,  such  as  a 
"  Nicol's  prism "  of  Iceland  spar,  is  found  to  be  polarized ;  that  is,  it  has  acquired 
opposite  and  complementary  properties  in  two  different  directions.  For  if  received 
by  a  second  similar  prism,  which  is  equally  transparent  in  all  positions  to  ordinary 
light,  the  polarized  ray  will  pass  through  it  only  when  the  principal  section  of  the 
second  prism  is  parallel  with  that  of  the  first ;  but  when  the  second  prism  is  turned 
round  90°,  the  light  is  arrested.  Now  if  certain  organic  substances  in  solution  be 
placed  between  the  two  prisms,  it  is  found  that  they  have  the  effect  of  changing  the 
angle  at  which  the  second  prism  must  stand  in  order  to  arrest  or  transmit  the  light 
from  the  first.  In  other  words,  the  plane  of  polarization  of  the  polarized  ray  has 
been  deviated  or  rotated  by  the  organic  liquid.  Some  substances  deviate  the  plane 
of  polarization  toward  the  right,  others  toward  the  left.  The  specific  rotary  power 
of  each  is  estimated  for  a  solution  of  standard  strength  and  quantity,  for  yellow 
light,  and  is  indicated  in  degrees  of  the  circle.  The  specific  rotary  power  of  dex- 
trine is  118°. 


54  PHYSIOLOGICAL    CHEMISTRY. 

the  alimentary  canal,  and  under  that  form  are  absorbed  into  the  cir- 
culation. 

It  is  evident,  therefore,  that  starch,  although  the  earliest  organic  mat- 
ter produced  by  vegetation,  is  not  the  form  under  which  it  takes  part 
in  nutrition.  It  is  mainly  formed  in  the  leaves,  but  remains  there  only 
as  a  temporary  product.  Its  granules  become  liquefied,  and  it  is  trans- 
ported, as  soluble  dextrine  or  sugar,  to  other  and  distant  parts  of  the 
plant.  There  it  resumes  the  solid  form,  and  is  either  changed  into  cel- 
lulose, for  the  woody  fibre  of  the  growing  tissues,  or  is  deposited  as 
starch  in  the  seeds,  tubers,  or  fleshy  roots  of  the  plant.  It  is  in  these 
situations  that  the  principal  accumulation  of  starchy  matter  takes  place; 
and  it  there  forms  a  reserve  material,  to  be  afterward  employed  for  the 
nutrition  of  animals,  or  for  the  growth  of  the  young  plant.  In  either 
case  it  again  undergoes  a  preliminary  transformation.  In  the  germina- 
tion of  a  seed,  its  starch  is  liquefied  by  conversion  into  dextrine  and 
sugar,  before  it  can  be  appropriated  by  the  growing  tissues ;  and  if  con- 
sumed as  food  by  man  or  animals,  it  undergoes  the  same  transformation 
in  the  digestive  process. 

Sugar. 

The  proximate  principles  designated  under  this  name  include  a  vari- 
ety of  substances  which  have  certain  well-marked  characters,  and  are 
of  frequent  occurrence  in  both  animal  and  vegetable  juices.  They  are 
crystallizable  and  soluble  in  water,  and  have,  when  in  solution,  a  sweet 
taste,  which,  in  some  varieties,  is  very  highly  developed.  They  are  all 
decomposed  by  heating  with  sulphuric  acid ;  their  hydrogen  and  oxygen 
being  driven  off,  while  the  carbon  remains  behind  as  a  black  deposit. 
In  this  condition  they  are  said  to  be  carbonized.  The  proportions  in 
which  they  occur  in  various  articles  of  food,  according  to  the  tables  of 
Payen,  Yon  Bibra,  and  a  few  other  observers,  are  as  follows : 

QUANTITY  OF  SUGAR  IN  100  PAETS  IN 

Cherries        .        .         .     18.12  Wheat  flour  .        .        .     2.33 

Apricots        .         .         .     16.48  Rye  flour       .         .         .     3.46 

Peaches         .        .        .11.61  Barley  meal  .        .        .    3.04 

Pears    ....     11.52  Oatmeal       .         .        .     2.19 

Juices  of  sugar-cane      .     18.00  Indian  corn  meal  .         .     3.71 

.Sweet  potatoes      .        .     10.20  Cow's  rnilk   .         .        .     5.20 

Beet  roots     .         .         .       8.00  Goat's  milk  .         .         .     5.80 

Parsnips        .        .        .      4.50  Beefs  liver   .        .        .1.79 

The  most  important  varieties  of  this  substance,  in  a  physiological 
point  of  view,  are  glucose,  cane  sugar,  and  milk  sugar. 

1.  Glucose,  C6Hla06. 

Glucose,  also  called  grape  sugar,  from  its  abundance  in  the  juice  of 
the  ripe  grape,  may  be  considered  as  the  representative  of  the  saccha- 
rine substances.  It  occurs  more  frequently  than  any  other  in  the  ani- 
mal fluids,  being  found  in  the  juices  of  the  liver,  in  the  chyle,  the  blood, 
and  the  lymph.  In  diabetes  it  is  abundantly  excreted  with  the  urine. 


HYDROCARBONACEOUS    SUBSTANCES.  55 

It  is  also  found  in  the  juices  of  many  plants,  in  various  sweet  fruits, 
and  in  honey,  where  it  is  associated  with  certain  other  varieties.  It  is 
freely  soluble  in  water.  Its  solution  has  a  moderately  sweet  taste,  and 
deviates  the  plane  of  polarization  toward  the  right  53.5°. 

It  is  this  form  of  sugar  which  is  produced  from  starch  by  boiling 
with  dilute  acids,  by  the  action  of  the  digestive  fluids,  and  in  the  plant 
during  germination.  The  change  consists  in  the  assumption  by  starch 
of  the  elements  of  water,  the  new  substance  thus  produced  being  still 
a  carbo-hydrate.  The  transformation  of  starch  into  glucose  is  there- 
fore represented  as  follows : 

STARCH.     WATER.      GLUCOSE. 
C6H1006  +  H20  =  OeH1206. 

Glucose  may  be  recognized  in  solution  by  various  tests.  First,  the 
action  of  alkalies  at  a  boiling  temperature.  If  a  solution  of  glucose 
be  heated  with  a  solution  of  potassium  hydrate,  the  sugar  is  decom- 
posed and  the  liquid  assumes,  first,  a  yellowish  and  then  a  brown  color, 
which  becomes  deeper  in  proportion  to  the  amount  of  glucose  and  alkali 
in  the  solution.  This  is  not  an  exclusive  test  for  glucose,  as  some  other 
organic  matters  are  discolored  in  a  similar  way  by  the  strong  alkalies ; 
but  it  will  serve  to  distinguish  it  from  cane  sugar,  which  does  not  pos- 
sess this  property. 

Secondly,  the  test  most  commonly  employed  for  glucose  depends 
upon  its  power  of  reducing  the  salts  of  copper  in  a  boiling  alkaline 
solution.  This  test,  which  is  known  as  "  Trommer's  test,"  is  applied 
in  the  following  manner:  A  small  quantity  of  copper  sulphate  in 
solution  is  added  to  the  suspected  liquid  and  the  mixture  rendered 
alkaline  by  the  addition  of  potassium  hydrate.  The  solution  then 
takes  a  blue  color.  On  boiling  the  mixture,  if  glucose  be  present,  the 
copper  suboxide  is  thrown  down  as  an  opaque  red,  yellow,  or  orange- 
colored  deposit ;  otherwise  no  change  takes  place.  In  this  reaction 
the  sugar,  which  is  oxidized  at  a  high  temperature  under  the  influence 
of  the  alkali,  takes  a  portion  of  its  oxygen  from  the  copper  salt  and 
reduces  it  to  the  form  of  insoluble  suboxide. 

Some  precautions  are  necessary  in  the  use  of  this  test.  As  a  general 
rule,  the  quantity  of  copper  sulphate  added  to  the  liquid  under  ex- 
amination, should  be  only  sufficient  to  give  a  distinct  blue  tinge  after 
the  addition  of  the  alkali.  If  the  copper  salt  be  used  in  excess,  the 
sugar  in  solution  may  not  be  sufficient  to  reduce  the  whole  of  it ;  and 
that  which  remains  as  a  blue  sulphate  may  mask  the  yellow  color  of 
the  suboxide  thrown  down  as  a  deposit.  This  difficulty  may  be  removed 
by  due  care  in  the  proportion  of  the  ingredients. 

Furthermore,  there  are  some  albuminous  substances  which  interfere 
with  the  test,  and  prevent  the  reduction  of  the  copper,  even  when 
sugar  is  present.  Certain  animal  matters,  to  be  described  hereafter, 
which  are  liable  to  occur  in  the  gastric  juice  and  in  the  blood,  have 
this  effect. 

The  ordinary  ingredients  of  the  urine  also  interfere  with  Trommer's 


56  PHYSIOLOGICAL    CHEMISTRY. 

test,  so  that  no  precipitate  takes  place  when  glucose  is  present,  although 
the  liquid  turns  yellow  on  boiling.  A  very  large  proportion  of  glucose 
may  be  added  to  fresh  urine  without  giving  rise  to  a  pulverulent  pre- 
cipitate on  the  application  of  the  test ;  notwithstanding  that,  if  dis- 
solved in  pure  water,  it  will  react  when  present  in  the  proportion  of 
one  part  to  10,000.  The  interference  of  urine  with  Trommer's  test 
depends,  not  upon  its  preventing  deoxidation,  but  upon  its  retaining 
the  reduced  copper  oxide  in  solution,  since  the  color  of  the  mixture 
changes  from  blue  to  yellow,  although  no  precipitate  takes  place.  It 
is  also  shown  by  Dr.  Fowler*  that  if  the  precipitate  resulting  from 
Trommer's  test  with  a  watery  solution  of  glucose  be  added  to  boiling 
urine,  it  is  redissolved.  The  same  observer  has  devised  a  method  of 
applying  the  test  to  urine  containing  glucose.  A  certain  quantity 
of  urine  can  dissolve  only  a  certain  amount  of  copper  oxide ;  and  if 
the  copper  sulphate  solution  be  added  to  a  specimen  of  saccharine  urine 
in  large  proportion,  the  excess  will  be  precipitated  and  show  itself  as 
a  deposit.  A  copper  sulphate  solution,  made  in  the  proportion  of  1  part 
copper  sulphate  to  7.5  parts  of  water,  and  added  to  saccharine  urine  to 
the  amount  of  one-half  or  one-third  its  bulk,  will  generally  produce  a 
satisfactory  reaction. 

All  such  sources  of  error  may  be  avoided  by  treating  the  suspected 
fluid  with  animal  charcoal,  or  by  evaporating  it  to  dryness,  extracting 
the  dry  residue  with  alcohol,  and  then  dissolving  the  dried  alcoholic 
extract  in  water,  before  applying  the  test.  Either  of  these  processes 
will  remove  the  substances  liable  to  interfere  with  the  test. 

A  more  delicate  reagent  for  glucose  is  that  known  as  "Fehling's 
liquor,"  which  is  an  alkaline  solution  of  a  double  copper  and  potas- 
sium tartrate.  It  is  made  as  follows : 

Pure  crystallized  copper  sulphate 40  grammes. 

Neutral  potassium  tartrate 1GO        " 

A  solution  of  sodium  hydrate  of  the  specific  gravity  1.12    650         " 

The  neutral  potassium  tartrate,  dissolved  in  a  little  water,  is  first 
mixed  with  the  solution  of  sodium  hydrate.  Then  the  copper  sulphate, 
dissolved  in  160  cubic  centimetres  of  water,  is  gradually  added  to  the 
alkaline  liquor,  which  assumes  a  clear,  deep  blue  color.  The  whole  is 
finally  diluted  with  water  to  the  volume  of  1154.4  cubic  centimetres. 
If  one  drop  of  this  liquid  be  added  to  one  cubic  centimetre  of  a  saccha- 
rine solution  and  heat  applied,  it  will  detect  one-fifteenth  of  a  milli- 
gramme of  glucose  by  the  reduction  of  the  copper  oxide.  One  advantage 
of  this  test  is  that  the  quantity  of  copper  salt  contained  in  a  given 
volume  is  accurately  known,  and  consequently  the  amount  of  glucose 
in  any  solution  may  be  determined  by  the  quantity  of  test  liquid  which 
it  decomposes  at  a  boiling  temperature.  One  cubic  centimetre  of 
Fehling's  liquor  is  exactly  decolorized  by  ^th  of  a  gramme  of  glucose. 

An  inconvenience  connected  with  Fehling's  liquor  is  that,  by  expo- 

*  New  York  Medical  Journal,  June,  1874,  p.  632. 


£ 


HYDROCARBONACEOUS    SUBSTANCES.  57 

sure  to  air  and  light,  it  undergoes  an  alteration,  in  which  some  of  its 
tartaric  acid  is  replaced  by  carbonic  acid.  In  this  condition  it  will  par- 
tially precipitate  on  boiling,  even  without  the  presence  of  sugar.  It 
should,  therefore,  be  kept  in  bottles  which  are  quite  full  and  protected 
from  the  light ;  and,  whenever  a  suspected  fluid  is  to  be  examined,  a 
small  portion  of  the  test-liquor  should  be  previously  boiled,  to  make 
sure  that  it  has  not  undergone  decomposition.  Although  by  exposure, 
at  a  summer  temperature,  Fehling's  liquor  may  become  altered  at  the 
end  of  a  week,  yet  if  protected  from  the  light,  in  carefully  closed  and 
full  bottles,  it  can  be  kept  unchanged  for  several  years. 

Thirdly,  one  of  the  most  marked  properties  of  glucose,  available  as 
a  test,  is  its  capacity  for  fermentation.     If  a  small  quantity  of  beer- 
yeast  be  added  to  a  glucose  solution,  and  the  mixture  kept  at  a  tem- 
perature of  25°  C.,  after  a  short  time  it  becomes  turbid.     It  then  begins 
to  liberate  carbonic  acid,  which  is  partly  dissolved  in  the  liquid  and 
partly  given  off  in  the  form  of  gas  bubbles,  which  rise  to  its  surface. 
From  this  circumstance  the  process  has  received  the  name  of  "  fermen- 
tation" or  boiling.     At  the  same  time  the  sugar  is  gradually  destroyed 
nd  alcohol  appears  in  its  place.     Finally  the  whole  of  the  glucose  is 
ecomposed,  having  been  converted  principally  into  alcohol  and  car- 
nic  acid.     The  transformation  is  expressed  as  follows : 
GLUCOSE.        ALCOHOL.      OAEBONIO  ACID. 
C6H1206  =  202H60     +       2C02. 

When  this  change  is  complete,  the  fermentation  stops  and  the  liquid 
becomes  clear,  its  turbid  contents  subsiding  to  the  bottom  as  a  whitish 
layer.  This  layer  is  itself  found  to  consist  of  yeast,  which  has  increased 
in  quantity  over  that  originally  added,  and  is  capable  of  exciting  fer- 
mentation in  other  saccharine  liquids. 

If,  instead  of  pure  glucose,  we  employ  the  expressed  juices  of  certain 
fruits,  like  those  of  the  grape,  which  contain  albuminoid  matters  in 
addition  to  glucose,  fermentation  begins  after  a  certain  period  of  ex- 
posure, and  goes  on  with  the  same  phenomena  as  before.  This  is  the 
source  of  all  the  vinous  and  alcoholic  fluids  used  by  man ;  namely,  the 
fermentation  of  fluids  containing  glucose  or  a  similar  saccharine  sub- 
stance. 

The  fermentation  of  glucose  is  due  to  the  action  of  a  colorless  micro- 
scopic fungus,  known  as  Saccharomyces.  This  plant  consists  of  cells, 
which  multiply  by  a  process  of  budding,  but  do  not  produce  filaments, 
nor  any  compound  vegetable  fabric.  The  species  present  in  beer-yeast 
is  the  "  Saccharomyces  cerevisiae."  Its  cells  are  usually  rounded  in 
?orm,  sometimes  oval  (Fig.  3).  They  vary  in  size,  the  greater  num- 

r  having  a  diameter  of  about  10  mmm.  They  have  a  thin  investing 
integument,  which  incloses  a  finely  granular  semi-solid  substance,  often 
containing  rounded  cavities  or  vacuoles  filled  with  fluid.  The  cells  are 
mostly  isolated,  but  occasionally  two  of  them  may  be  seen  adhering 
together.  There  is  a  small  amount  of  intercellular  liquid,  containing 
albuminous  matter  and  mineral  salts. 


58 


PHYSIOLOGICAL    CHEMISTEY. 


FIG.  3. 


SACCHAROMYCES  CEREVISI.E,  in  its  quiescent  con- 
dition ;  from  deposit  of  beer-yeast,  after  fermen- 
tation. 


FIG.  4. 


When  yeast  is  added  to  a  warm   solution  of  glucose,  the  cells  of 

the  yeast-plant  after  a  short  time 
begin  to  multiply  by  budding. 
The  buds  increase  rapidly  in  size, 
and,  when  the  young  cell  has  be- 
come nearly  as  large  as  its  pa- 
rent, it  usually  separates  and  be- 
gins an  independent  existence. 
While  in  this  condition  the  cells 
are  mostly  oval  in  form,  with 
an  average  diameter  of  but 
little  more  than  8  mmm.  Often 
two  or  three  are  seen  con- 
nected together,  forming  monil- 
iform  chains.  It  is  by  the 
active  growth  and  development 
of  the  cells  during  this  process 
that  the  glucose  of  the  solution  is 
decomposed,  and  alcohol  and  car- 
bonic acid  produced  in  its  place. 
Another  species  of  saccharomyces  forms  the  fungus  of  bread-yeast, 

and  a  third  the  ferment  of  grape- 
juice,  by  which  it  is  made  to 
undergo  the  vinous  fermenta- 
tion. 

When  fermentation  is  used  as 
a  test,  a  little  beer-yeast  is  added 
to  the  supposed  saccharine  fluid, 
and  the  mixture  kept  at  the 
temperature  of  25°  C.  The  gas 
given  off  during  the  process  is 
collected  and  examined,  and  the 
remaining  fluid  is  purified  by 
distillation.  If  the  gas  evolved 
be  carbonic  acid,  and  if  the  dis- 
tilled liquid  contain  alcohol,  there 
can  be  no  doubt  that  a  ferment- 
able sugar  wras  present  in  the 
solution.  Glucose  undergoes  fer- 
mentation more  readily  and  more  completely  than  tie  other  varieties 
of  sugar. 

2.  Lactose,  C12HMO12,  Sugar  of  Milk. 

Lactose  is  the  saccharine  ingredient  of  milk,  the  only  fluid  in  which 
it  is  known  to  occur.  It  is  less  freely  soluble  than  glucose,  and  is  less 
sweet  to  the  taste.  In  watery  solution  it  rotates  the  plane  of  polari- 
zation to  the  right  58°. 20.  In  chemical  composition  it  is  isomeric  with 
glucose,  which  it  resembles  in  being  decomposed  and  turned  brown  by 


SACCHAROMYCES  CEREVISI^E  in  active  germination. 
From  fermenting  saccharine  solution. 


HYDROCARBONACEOUS    SUBSTANCES.  59 

boiling  alkalies,  in  reducing  the  copper-oxide  in  Trommer's  and  Fehling's 
tests,  and  in  undergoing  the  alcoholic  fermentation  by  the  influence 
of  yeast.  It  enters  into  fermentation,  however,  very  slowly,  as  com- 
pared with  glucose,  and  the  process  is  usually  incomplete.  In  the 
fermentation  of  milk,  a  part  of  its  sugar  is  converted  into  lactic  acid, 
C3H603,  also  a  carbo-hydrate.  By  boiling  with  dilute  sulphuric  or 
hydrochloric  acid,  lactose  becomes  readily  and  completely  fermentable. 
This  sugar  forms  an  important  element  in  the  food  of  the  infant,  in 
which  it  is  a  constant  ingredient.  It  is  formed  in  the  mammary  gland, 
probably  by  transformation  from  glucose,  but  the  exact  method  of  its 
production  is  unknown.  It  is  discharged  with  the  milk,  as  a  reserve 
material  for  the  nutrition  of  the  infant. 

3.  Saccharose,  C12H22OU,  Cane  Sugar. 

This  variety,  the  oldest  known  species  of  sugar,  is  derived  from  the 
juices  of  the  sugar-cane,  where  it  exists  in  great  abundance.  It 
solidifies,  on  cooling  from  a  hot  concentrated  solution,  in  white  granular 
crystalline  masses ;  the  form  in  which  it  is  generally  used  for  culinary 
purposes.  If  crystallized  more  slowly  it  furnishes  large,  colorless, 
prismatic  crystals,  known  as  "rock  candy"  or  "sugar  candy."  This 
sugar  is  also  obtained  from  the  juices  of  the  beet-root,  and,  im- 
perfectly purified,  from  those  of  the  sorghum  and  the  sugar-maple.  It 
exists  to  some  extent  in  the  green  stems  of  Indian  corn,  in  sweet 
potatoes,  in  parsnips,  turnips,  and  carrots,  and  in  the  spring  juices  of 
the  birch  and  walnut  trees.  Honey  is  a  mixture  of  glucose  and  saccha- 
rose with  various  other  substances. 

Cane  sugar  originates  from  glucose,  in  the  process  of  vegetation,  by 

a  change  the  reverse  of  that  by  which  glucose  is  formed  from  starch, 

that  is,  by  dehydration.     A  comparison  of  the  chemical  composition  of 

the  two  substances  will  show  the  manner  in  which  the  transformation 

ikes  place,  namely : 

GLUCOSE.       WATER.   CANE  SUGAR. 
2(06H1206)-II20  =  C12H22011. 

Saccharose  is  the  most  soluble  of  the  sugars,  and  has  the  strongest 
weet  taste.  It  rotates  the  plane  of  polarization  to  the  right  73°. 84. 
It  differs  from  glucose  by  the  fact  that  it  is  not  turned  brown  by  boiling 
with  an  alkali,  and  does  not  reduce  the  copper-oxide  in  Trommer's  test. 
It  may  be  converted  into  glucose,  however,  by  a  few  seconds'  boiling 
with  a  dilute  mineral  acid,  and  will  then  react  promptly  with  boiling 
alkalies  and  with  Trommer's  test.  Cane  sugar  is  not  immediately 
rmentable,  but  by  contact  with  yeast  it  is  after  a  time  changed  into 
glucose,  and  finally  enters  into  fermentation.  In  the  living  vegetable 
tissues  it  represents  a  reserve  material,  and  is  subsequently  reconverted 
into  glucose  for  the  purposes  of  nutrition.*  When  taken  as  food,  it  is 
transformed  into  glucose  by  the  intestinal  fluids. 


*  Mayer:  Agrikultur-Chemie.     Heidelberg,  1871.      Band  I.,  p.  122. 


60  PHYSIOLOGICAL    CHEMISTRY. 

Sugar  and  starch,  accordingly,  in  all  their  varieties,  are  closely  allied, 
both  in  their  chemical  and  physiological  relations.  They  are  all  carbo- 
hydrates, and  their  mutual  convertibility  in  the  vegetative  process  has 
been  shown  by  abundant  investigations.  Starch  and  sugar,  in  the 
living-  plant,  represent  the  same  nutritive  material  under  two  different 
conditions ;  starch  having  the  form  of  a  solid  deposit,  glucose  that  of 
solution  and  activity.  The  organic  substance  passes  from  one  to  the 
other  of  these  two  conditions  by  hydration  or  dehydration.  It  is  at 
last  either  decomposed  in  the  immediate  changes  of  nutrition,  or  is 
stored  up  as  a  deposit  for  future  consumption. 

Glycogen,  C6H10O5. 

Glycogen,  so  called  from  its  capacity  for  the  production  of  glucose,  is 
an  amylaceous  substance  of  animal  origin.  It  is  isomeric  with  starch 
and  dextrine,  and  resembles  the  latter  in  its  physical  properties,  except 
that  a  watery  solution  of  dextrine  is  clear,  while  that  of  glycogen  is 
opalescent,  and  that  when  treated  with  iodine,  dextrine  in  solution 
gives  a  rosy  red,  glycogen  a  deep  brown-red  color.  It  is  insoluble  in 
alcohol  and  in  ether,  but  soluble  in  water,  either  cold  or  hot.  Its  watery 
solution  deviates  the  plane  of  polarization  strongly  to  the  right,  its 
specific  power  of  rotation  for  yellow  light  being  about  130°. 

This  substance  is  constantly  present  in  the  tissue  of  the  liver  in  all 
vertebrate  animals,  in  the  healthy  condition.  It  is  found  at  an  early 
period  of  development  in  the  integument  and  mucous  membranes  of 
the  embryo,  in  a  portion  of  the  placenta  and  amnion,  in  the  muscles 
during  their  formative  condition,  and  in  the  pulmonary  tissue.  It  does 
not  exist  at  this  time  in  the  liver,  or  in  any  other  of  the  glandular 
organs.  But  about  the  middle  of  foetal  life  it  begins  to  be  found  in 
the  liver,  where  it  increases  in  quantity,  at  the  same  time  gradually 
disappearing  from  the  other  organs  ;  and  after  birth  it  is  a  character- 
istic and  abundant  ingredient  of  the  liver  alone.  It  has  been  found, 
however,  in  moderate  and  varying  amount  in  the  muscles  of  some 
adult  quadrupeds  and  birds,  and  in  considerable  quantity  in  molluscous 
animals,  as  the  oyster  and  the  cockle-shell. 

Glycogen  is  obtained  from  the  liver  of  a  well-fed  animal  in  the  fol- 
lowing manner  :  The  organ  is  taken  out  immediately  after  death  and 
cut  into  small  pieces,  which  are  then  coagulated  by  a  short  immersion 
in  boiling  water.  This  arrests  the  changes  which  would  otherwise  take 
place  under  the  influence  of  a  ferment  contained  in  the  hepatic  juices. 
The  coagulated  tissue  is  then  ground  to  a  pulp  and  boiled  for  half  an 
hour  with  a  small  quantity  of  water,  making  a  concentrated  decoction, 
which  is  afterward  treated  with  animal  charcoal,  to  remove  the  color- 
ing matters,  and  filtered.  The  filtered  decoction  is  opaline,  but  does 
not  hold  in  suspension  any  solid  granular  matters  visible  with  the 
microscope.  It  is  allowed  to  fall  by  drops  into  strong  alcohol,  by  which 
the  dissolved  glycogen  is  precipitated,  subsiding  to  the  bottom  a?  a  white 
deposit.  It  is  still  contaminated  by  a  little  glucose,  a  certain  quantity 


HYDROCARBONACEOTJS    SUBSTANCES.  61 

of  biliary  salts,  and  some  albuminous  matters.  The  glucose  and  biliary 
salts  are  removed  by  washing  the  precipitate  with  alcohol.  The  remain- 
der is  then  boiled  for  a  quarter  of  an  hour  with  a  concentrated  solution 
of  potassium  hydrate,  which  dissolves  the  albuminous  matters,  but  does 
not  affect  glycogen.  After  filtration  it  is  again  dissolved  in  water,  the 
traces  of  alkali  removed  by  the  addition  of  a  little  acetic  acid,  and  the 
glycogen  re-precipitated  by  alcohol  in  excess.  It  is  then  dried  and  may 
be  kept  in  the  form  of  a  white  pulverulent  mass,  which  retains  its  prop- 
erties for  an  indefinite  time. 

In  watery  solution  it  exhibits  the  characteristic  properties  of  an  amy- 
laceous substance,  being  converted  into  sugar  by  all  agencies  which 
have  a  similar  effect  on  starch,  namely,  by  boiling  with  a  dilute  mineral 
acid,  and,  at  a  moderately  warm  temperature,  by  the  contact  of  saliva, 
the  pancreatic  or  intestinal  juices,  or  the  serum  of  blood.  If  allowed  to 
remain  in  the  liver  after  death,  or  brought  in  contact  with  its  tissue 
after  removal,  a  portion  is  transformed  into  glucose  by  the  albuminous 
matters  of  the  hepatic  substance. 

The  quantity  of  glycogen  in  the  liver  varies,  with  the  kind  of  food 
used,  from  about  t  to  It  per  cent.  It  is  more  abundant  with  vegetable 
than  with  animal  food,  and  is  most  abundant  of  all  under  a  diet  of  carbo- 
hydrates. It  increases  after  digestion,  and  diminishes  with  fasting, 
disappearing  altogether  after  an  abstinence  of  four  or  five  days.  It 
will  then  reappear  very  rapidly  after  a  meal  of  starchy  or  saccharine 
matters.  From  these  facts  it  is  apparent  that  glucose,  when  taken  as 
food,  or  absorbed  from  the  alimentary  canal,  is  deposited  in  the  liver 
under  the  form  of  glycogen.  The  change  which  takes  place  is  a  dehy- 
dration, as  follows : 

GLUCOSE.     WATER.     GLYOOGEN. 
C6H1206-II20  =  C6H1005. 

While  in  this  condition  the  glycogen  forms  part  of  the  substance  of 
the  liver,  and  is  probably  a  material  of  reserve,  to  be  afterward  con- 
sumed in  some  other  part  of  the  body.  It  appears  to  be  gradually 
reconverted  into  glucose  in  the  intervals  of  digestion,  and  to  disappear 
under  this  form  from  the  hepatic  tissue. 

Glycogen  presents  accordingly,  in  every  respect,  a  strong  analogy  with 
vegetable  starch.  Its  abundant  presence  in  the  embryonic  organs,  from 
which  it  disappears  when  they  have  acquired  their  growth,  is  like  the 
deposit  of  starch  in  a  seed,  to  be  used  up  in  the  act  of  germination.  And 
in  the  adult  animal  it  is  probable  that  a  large  portion,  if  not  all,  of  the 
carbo-hydrates  taken  as  food  pass  through  the  glycogenic  condition  be- 
fore they  are  finally  employed  in  the  nutrition  of  the  body. 

Fats, 

The  fats  form  a  well  marked  group  of  organic  bodies  which  a're  widely 
diffused  both  in  the  vegetable  and  the  animal  kingdom.  They  are  dis- 
tinguished from  the  carbo-hydrates,  first,  by  the  fact  that  they  do  not 
contain  hydrogen  and  oxygen  in  the  proportion  to  form  water,  the 


62  PHYSIOLOGICAL    CHEMISTRY. 

oxygen  being  present  in  smaller  quantity ;  and  secondly,  by  their  large 
proportion  of  carbon,  which  constitutes  on  the  average  a  little  over  75 
per  cent,  of  their  weight.  This  fact  is  probably,  connected  with  their 
inflammability,  the  oils  being  oxidized  at  a  temperature  of  300°  C.,  and 
burning  with  a  bright  flame  The  smooth  consistency  of  oleaginous 
matters  is  also  one  of  their  distinguishing  features,  and  enables  them 
to  be  employed  as  lubricating  substances,  to  diminish  the  friction  be- 
tween opposite  surfaces.  In  the  pure  condition  they  are  destitute  of 
taste  and  odor.  They  are  all  liquid  at  moderately  high  temperatures, 
and  solidify  by  crystallization  when  cooled  down  to  a  certain  point, 
which  is  different  for  each  variety.  The  fatty  substances  which  at  or- 
dinary temperatures  have  a  thick,  solid,  or  semi-solid  consistency,  are 
more  especially  designated  as  "  fats  ;"  those  which  are  more  liquid  are 
spoken  of  as  "oils."  They  have  no  rotatory  action  on  polarized  light. 
They  are  insoluble  in  water,  and  do  not  mix  with  it  except  by  mechan- 
ical agitation ;  after  which  the  two  fluids  separate  from  each  other  ac- 
cording to  their  specific  gravity,  the  water  remaining  below  and  the  oil 
rising  to  the  surface  in  a  distinct  layer.  Fats  and  oils  are  slightly 
soluble  in  alcohol,  and  freely  soluble  in  ether,  which  is  used  to  extract 
them  from  admixture  with  other  organic  substances. 

Fatty  matters  are  found  in  varying  quantity  in  different  vegetable 
tissues,  the  most  abundant  deposit  occurring  in  nuts,  fruits,  and  seeds, 
particularly  those  of  the  sweet  and  bitter  almond,  the  chocolate  tree, 
hemp,  flax,  Ricinus  communis,  and  Croton  tiglium,  in  which  last  it  is 
in  the  proportion  of  60  per  cent.  The  seeds  of  plants  generally  are 
designated  as  "starchy  "  or  "oleaginous,"  according  to  the  preponder- 
ance of  one  or  the  other  of  these  substances  in  their  tissue.  In  the 
animal  body,  fat  is  most  abundant  in  the  adipose  tissue  and  in  the  mar- 
row of  the  long  bones,  where  it  amounts  to  from  80  to  96  per  cent. 
In  the  human  subject,  under  normal  conditions,  the  entire  quantity  of  fatty 
matters  has  been  estimated  at  from  2.5  to  5  per  cent,  of  the  bodily  weight.* 

The  following  list  gives  the  proportion  of  fat  in  various  alimentary 
substances,  according  to  the  tables  of  Payen  : 

QUANTITY  OF  FAT  IN  100  PARTS  IN 

Wheat        .  .  .  2.10  Beef's  flesh  (average)  5.19 

Indian  corn  .  .  8.80  Calf's  liver  .  .  5.58 

Potatoes      .  .  .  0.11  Mackerel   .  .  .  6.76 

Beans.        .  .  .  2.50  Salmon      .  .  .  4.85 

Peas    ....  2.10  Oysters     .  .  .  1.51 

Sweet  almonds  .  .  24.28  Cow's  milk  .  .  3.70 

Chocolate  nut  .  .  49.00  Fowl's  egg  .  .  7.00 

Beside  entering  as  an  ingredient  into  the  above  articles,  fat  is  often 
taken  with  the  food  in  a  pure,  or  nearly  pure,  form,  as  butter,  olive  oil, 
or  adipose  tissue. 

Origin  of  Fatty  Substances. — The  first  production  of  these  organic 

*Gorup  Besanez:  Physiologischen  Chemie.     Braunschweig,  1878,  p.  169. 


HYDROCARBONACEOTJS    SUBSTANCES.  63 

matters  takes  place  in  the  act  of  vegetation,  in  all  probability  by  a  meta- 
morphosis of  starch  or  sugar  already  formed.  This  is  the  origin  of 
fatty  matters  generally  recognized  by  vegetable  physiologists.  In  this 
change  the  proportions  of  carbon  and  hydrogen  are  increased  50  or  60 
per  cent.,  while  that  of  the  oxygen  is  largely  diminished.  By  itself, 
accordingly,  it  would  be  a  reducing  process,  similar  to  that  by  which 
starch  is  first  formed  from  inorganic  matter.  But  this  is  not  the  view 
usually  entertained  in  regard  to  it.  The  deoxidation  of  carbonic  acid 
and  water  can  take  place,  so  far  as  we  know,  only  in  the  chlorophylle- 
holding  cells  of  the  plant ;  and  fatty  matter  is  often  produced,  as  in  oily 
seeds,  where  no  chlorophylle  is  present.  It  is  possible  that  the  reduc- 
tion of  the  quantity  of  oxygen,  during  the  conversion  of  starchy  mat- 
ters into  fat,  may  be  accompanied  by  the  liberation  of  carbonic  acid, 
and  the  formation  of  other  highly  oxidized  substances,  which  would 
account  for  the  diminished  proportion  of  oxygen  remaining.  Some- 
thing of  this  sort  takes  place  in  the  alcoholic  fermentation  of  glu- 
cose, already  described  (page  51),  as  follows: 

GLUCOSE.          ALCOHOL.         CARBONIC  ACID. 
06H1206  =    2C,H60      +         2C02. 

Here  the  alcohol  produced  by  fermentation  contains  a  smaller  pro- 
portion of  oxygen  than  the  original  glucose ;  but  another  body  (car- 
bonic acid),  containing  a  larger  proportion,  has  been  liberated  at  the 
same  time.  The  missing  oxygen  therefore  has  not  been  discharged  in 
the  free  condition,  but  in  a  more  stable  form  of  combination  than  be- 
fore. A  similar  change  taking  place  in  the  starchy  or  saccharine  matters 
of  a  plant,  with  the  production  of  fat,  would  not  be  altogether  a  deoxi- 
dation, but  would  include  a  rearrangement  of  the  chemical  elements, 
with  the  simultaneous  production  of  other  compound  bodies.  . 

There  are  no  means  at  present  known  by  which  the  transformation 
of  starch  into  fat  can  be  artificially  accomplished,  and  even  its  chemical 
formula  cannot  be  expressed  with  any  reasonable  certitude.  But  there 
are  well-known  facts  which  make  it  highly  probable  that  such  a  change 
may  be  and  is  effected  in  the  tissues  of  the  living  plant.  In  the  first 
place,  it  is  certain  that  starch  disappears  from  the  leaves  in  which  it  is 
produced,  to  be  transported  under  a  soluble  form  to  other  organs. 
Secondly,  there  are  instances  of  the  production  of  oily  seeds,  or  other 
fatty  reservoirs,  in  plants  where  no  other  deposit  than  that  of  starch 
can  be  detected  in  their  chlorophylle-holding  leaves.*  And,  thirdly, 
the  oily  seeds  of  certain  plants  while  still  immature  contain  starch,  but 
as  they  ripen  the  starch  diminishes  or  disappears  and  oil  takes  its  place.f 

Varieties  of  Fat. — The  most  important  and  abundant  varieties  of 
fat  are  Stearine,  Palmitine,  and  Oleine.  They  resemble  each  other  in 
general  character,  and  differ  mainly  in  their  degree  of  consistency, 
stearine  being  the  most  solid  at  ordinary  temperatures,  while  palnii- 

*  Mayer :  Agrikultur  Chemie.     Heidelberg,  1871.     Band  L,  p.  86. 
f  Johnson:  How  Crops  Grow.     New  York,  p.  94. 


64  PHYSIOLOGICAL    CHEMISTRY. 

tine  holds  an  intermediate  position  in  this  respect,  and  oleine  is  the 
most  fluid. 

1.  Stearine,  C57Hno06, 

So  called  from  the  readiness  with  which  it  assumes  the  solid  form,  is  a 
main  ingredient  of  the  more  consistent  fats.  It  liquefies  at  66°. 5  C., 
and  again  solidifies  when  the  temperature  falls  below  this  point.  It 
crystallizes,  on  cooling  from  a  warm  solution  in  oleine,  in  fine  radiating 
needles,  which  often  follow  a  wavy  or  curvilinear  direction.  It  is  rather 
less  soluble  in  alcohol  and  ether  than  the  other  fatty  substances. 

2,  Palmitine,  C51H9806, 

Was  first  recognized  as  an  ingredient  of  palm  oil,  a  semi-solid  fat 
obtained  from  the  seed  of  an  African  palm.  It  crystallizes,  on  cooling 
from  its  concentrated  alcoholic  or  ethereal  solution,  in  the  form  of 
slender  needles.  It  liquefies  at  60°  C.  It  occurs  abundantly  in  a 
variety  of  animal  and  vegetable  fats. 

3,  Oleine,  C57H10406. 

As  its  name  indicates,  this  is  the  representative  ingredient  of  the  oils, 
or  liquid  fatty  substances.  When  pure  it  is  transparent  and  colorless. 
It  retains  its  fluidity  at  ordinary  temperatures,  and  even  below  the 
freezing  point  of  water.  It  readily  dissolves  both  stearine  and  palmi- 
tine,  its  solvent  power  increasing  with  the  elevation  of  the  temperature. 

Physical  and  Chemical  Changes  of  the  Fatty  Substances. — There  are 
certain  changes  of  condition  produced  in  the  fats  by  external  influences 
which  are  characteristic  of  these  substances  as  a  class.  The  first  is 
that  by  which  an  oily  substance,  when  mingled  with  a  watery  liquid, 
is  reduced  to  the  state  of  an  emulsion ;  that  is,  a  mixture  in  which 
the  oil  is  broken  up  into  minute  particles  and  uniformly  disseminated 
through  the  watery  liquid.  This  change  will  not  take  place  when  oil 
is  added  to  pure  water,  or  to  a  watery  solution  of  neutral  or  acid  salts. 
But  if  a  trace  of  alkali  or  alkaline  carbonate  be  present,  the  fatty  sub- 
stance is  at  once  disseminated  throughout  the  mass,  and  held  in  per- 
manent suspension.  In  such  a  mixture  there  is  no  change  in  the  chem- 
ical characters  of  either  the  oil  or  the  watery  liquid,  but  only  in  their 
physical  condition ; — the  two  being  retained  in  contact  with  each  other 
in  a  state  of  minute  subdivision.  By  evaporation  the  watery  parts 
may  be  separated  and  the  oil  left  behind  unaltered.  An  emulsion  formed 
in  this  way  is  whitish  or  white  in  color,  and  opalescent  or  opaque, 
according  to  the  proportion  of  oily  matter  present.  The  emulsion  of  oil 
may  also  be  accomplished  by  certain  organic  matters  in  watery  solu- 
tion, especially  by  the  albumen  of  egg,  or  the  albuminous  ingredients  of 
the  blood  and  secretions.  It  is  under  this  form  that  oily  matters  exist, 
when  in  considerable  quantity,  in  the  animal  fluids,  such  as  the  milk, 
the  chyle,  or  the  blood. 

Another  change  which  may  be  produced  in  the  fats  is  that  of  saponi- 
fication.  This  is  a  chemical  change  in  which  the  oily  substance  loses 


HYDROCARBONACEOUS  SUBSTANCES. 


its  original  character,  and  its  elements  appear  under  new  forms  of  com- 
bination.   When  an  oily  or  fatty  matter  is  kept  for  some  hours  at  a  high 
temperature  in  emulsion  with  water  and  an  alkali,  it  is  decomposed 
with  the  assimilation  of  the  elements  of  water,  producing  a  fatty  acid 
and  glycerine.     The  change  which  takes  place  is  as  follows : 
STEARINE.         WATER.       STEARIC  ACID.       GLYCERINE. 
C57H11006   +   3H20   =   C54H10806    +     03H8O3. 
The  acid  product  is  stearic,  palmitic,  or  oleic  acid,  according  to  the 
variety  of  fat  used ;  and,  when  set  free,  it  unites  with  the  alkali,  form- 
ing a  neutral  stearate,  palmitate,  or  oleate.     In  such  a  combination  the 
oil  is  said  to  be  saponified,  and  in  this  form  becomes  more  or  less  sol- 
uble in  watery  and  serous  liquids.     Oil  may  be  also  decomposed  by 
means  of  superheated  steam,  with  the  production  of  glycerine  and  free 
fatty  acid,  the  latter  of  which  is  then  easily  saponified  by  either  a  caus- 
tic alkali  or  an  alkaline  carbonate. 

There  is  some  doubt  whether  the  saponification  of  fat  takes  place  in 
the  animal  body.  Saponified  fats  are  enumerated  by  some  observers  as 
constant  ingredients  of  the  blood-plasma,  while  their  presence  is  denied 
by  others.  All  agree  that  if  present  they  are  in  extremely  minute 
proportion,  by  far  the  larger  quantity  of  fat  retaining  its  chemical  char- 
acters so  long  as  it  can  be  traced  in  the  circulation. 

Condition  of  Fatty  Matters  in  the  Living  Body. — None  of  the  fatty 
substances  occur  naturally  in  an  isolated  form,  but  they  are  mingled  in 
varying  proportions  in  all  the  ordinary  animal  and  vegetable  fats  and 
oils.  The  consistency  of  the  mixture  varies  with  the  relative  quantity 
of  its  ingredients.  The  more  solid  fats,  such  as  suet  and  tallow,  consist 

;gely  of  stearine ;   the  softer 
s,  as  lard,  butter,  and  those  FlG-  5- 

human  adipose  tissue,  contain 
greater  abundance  of  palmi- 
e ;  while  the  liquid  fats,  like 
i  oils,  olive  oil,  and  nut  oil, 
are  composed  mainly  of  oleine. 
s  a  general  rule,  in  the  warni- 
ooded  animals,  these  mixtures 
'e    fluid,    or    nearly   so ;    for, 
though  both  stearine  and  pal- 
itine,  when  pure,  are  solid  at 
e   temperature   of  the   body, 
ey  are  held  in  solution  during 
e  by  the  oleine  with  which 
ey  are  associated. 
As  the  body  cools  after  death, 

.         .  -,        ,      ...  OLEAGINOUS  SUBSTANCES  OF  HUMAN  FAT.    Stearine 

e  stearine  and  palmitme  some-          aud  Paimitine  crystallized ;  oieine  fluid, 
les  separate  in  a  crystalline 
)rm,  since  the  oleine  can  no  longer  hold  the  whole  of  them  in  solution, 
'ig.  5.) 

E 


66  PHYSIOLOGICAL    CHEMISTRY. 

When  in  a  fluid  state  the  fatty  substances  present  themselves  in  the 
form  of  drops  or  globules  of  various  sizes,  which  may  be  recognized  by 
their  optical  properties.  They  are  circular  in  shape,  with  a  well- 
defined  outline.  They  often  have  a  faint  amber  color,  which  is  dis- 
tinctly marked  in  the  larger  globules,  less  so  in  the  smaller.  As  they 
are  more  highly  refractive  than  the  watery  fluids  in  which  they  are 
immersed,  they  act  as  double  convex  lenses,  and  concentrate  the  light 
transmitted  through  them  at  a  point  above  the  level  of  the  liquid. 
Consequently,  they  present  the  appearance  of  a  bright  centre  sur- 
rounded by  a  dark  border.  If  the  lens  of  the  microscope  be  lifted 
farther  away,  the  centre  of  the  globule  becomes  brighter  and  its  bor- 
ders darker.  These  characters  will  usually  be  sufficient  to  distinguish 
them  from  other  fluid  globules  of  less  refractive  power. 

The  oleaginous  matters  present  a  striking  peculiarity  in  regard  to 
the  form  under  which  they  occur  in  the  living  body,  and  by  which  they 
are  distinguished  from  the  remainder  of  its  ingredients.  Instead  of 
combining  with  the  other  constituents  of  the  animal  solids  and  fluids, 
in  homogeneous  union  or  solution,  they  are  deposited,  as  a  rule,  in  dis- 
tinct masses  or  globules,  suspended  in  the  serous  fluids,  interposed 
between  the  anatomical  elements,  included  in  the  interior  of  cells,  or 
deposited  in  the  substance  of  fibres  or  membranes.  Even  in  the  v 
table  tissues,  they  are  always  in  the  form  of  drops  or  granules. 

Owing  to  this  fact  the  oils  can  usually  be  extracted  by  mechanical 
means.  The  tissues  are  cut  into  small  pieces  and  subjected  to  pres- 
sure, by  which  the  oil  is  forced  out  from  the  parts  in  which  it  was 
entangled,  and  separated,  without  further  manipulation,  in  a  state  of 
comparative  purity.  A  moderately  elevated  temperature  facilitates  the 
operation  by  increasing  the  fluidity  of  the  oleaginous  matter ;  but  no 
chemical  agency  is  required  for  its  separation.  Under  the  microscope, 
oil-drops  and  granules  can  be  distinguished  from  the  remaining  parts  by 
their  optical  properties  and  by  the  action  of  ether,  which  dissolves  them, 
for  the  most  part,  without  attacking  other  neighboring  substances. 

In  the  adipose  tissue  the  oils  are  contained  in  the  interior  of  vesicles, 
the  cavities  of  which,  in  a  state  of  health,  they  completely  fill.  The 
adipose  vesicle,  which  varies  in  diameter,  in  man,  from  28  mmm.  to 
125  mrnm.,  is  composed  of  a  thin  membrane,  forming  a  closed  sac,  in 
which  the  oily  matter  is  included.  Sometimes,  in  cases  of  emaciation, 
the  oil  partially  disappears  from  the  cavity  of  the  vesicle,  its  place  being 
taken  by  a  watery  serum  ;  but  the  serous  and  oily  fluids  remain  distinct 
in  the  vesicular  cavity. 

In  the  chyle,  the  oleaginous  matter  is  in  a  state  of  emulsion,  and  its 
subdivision  is  here  more  complete  than  anywhere  else  in  the  body.  It 
presents  the  appearance  of  a  fine  granular  dust,  known  as  the  "molecu- 
lar base  of  the  chyle."  A  few  of  its  granules  measure  2.5  mmm.  in 
diameter;  but  they  are  generally  much  less  than  this,  and  the  greater 
part  are  so  small  that  they  cannot  be  accurately  measured.  (Fig.  (>.) 
For  the  same  reason  they  do  not  present  the  brilliant  centre  and  dark 


HYDROCARBONACEOUS  SUBSTANCES. 


67 


FIG.  6. 


CHYLE,  from  commencement  of  Thoracic  Duct,  from 
the  Dog. 


border  of  large  oil-globules ;  but  appear  by  transmitted  light  only  as 
minute  granules.  The  white 
color  and  opacity  of  the  chyle, 
as  of  other  fatty  emulsions,  de- 
pend upon  this  molecular  condi- 
tion of  the  oily  ingredients.  The 
albumen  and  salts,  which  are  in 
intimate  union  with  each  other, 
and  with  the  water,  would  alone 
make  a  colorless  and  transparent 
fluid ;  but  the  oily  matters,  sus- 
pended in  distinct  particles,  with 
a  different  refractive  power  from 
that  of  the  serous  fluid,  interfere 
with  its  transparency,  and  give 
to  the  mixture  its  diffused  white 
color.  The  oleaginous  nature  of 
the  particles  is  shown  by  their 
solubility  in  ether. 

In  milk  the  oily  matter  occurs  in  larger  masses,  or  "  milk-globules," 
which  have  an  average  diameter  of  6  mmm.  They  are  not  quite  fluid, 
but  have  a  pasty  consistency,  owing  to  the  large  quantity  of  palmitine 
which  they  contain,  as  compared  with  the  oleine ;  and  under  the 
microscope  they  present  accordingly  a  somewhat  irregular  outline. 
By  heating  the  milk  they  may  be  completely  liquefied,  and  made  to 
assume  a  globular  form.  When  forcibly  beaten  into  a  mass  by  churn- 
ing, they  constitute  butter. 

In  certain  parts  of  the  body  oil-drops  and  granules  are  deposited  in 

the  substance  of  cells  or  other  ana- 
tomical elements ;  as  in  the  laryn- 
geal,  tracheal,  and  costal  carti- 
lages, and  the  secreting  cells  of 
the  sebaceous  glandules.  Oily 
matter  also  occurs,  under  the  same 
form,  in  the  glandular  cells  of  the 
human  liver,  where  it  is  a  con- 
stant ingredient  in  a  state  of 
health.  In  certain  cases  of  dis- 
ease it  accumulates  in  excessive 
quantity,  producing  a  fatty  de- 
generation of  the  organ. 

In  the  carnivorous  animals  it 
exists  normally  in  the  epithelium 
cells  of  the  convoluted  portion 

GLOBULES  OF  Cow's  MILK.  „  , ,  .    .  _  .    i_    i  mu 

of  the  urmiferous  tubules.     The 

drops  and  granules  are  here  so  numerous  as  often  to  fill,  apparently,  the 
whole  calibre  of  the  tubules. 


FIG.  7. 


68 


PHYSIOLOGICAL    CHEMISTRY. 


In  the  marrow  of  the  long  bones  it  is  more  abundant  than  in  any 

other  tissue,  occurring  both  in- 

FlG-  8-  closed    in  vesicles   and   in   the 

form  of  free  oil-drops.  It  exists 
in  considerable  quantity  in  the 
yellow  wall  of  the  corpus  luteum. 
It  is  also  deposited  in  the  sub- 
stance of  muscular  fibres  under 
various  conditions  ;  in  those  of 
the  voluntary  muscles  after  pro- 
longed disuse,  those  of  the  heart 
in  fatty  degeneration  of  this  or- 
gan, and  those  of  the  uterus  after 
delivery.  In  the  uterine  muscu- 
lar fibres  it  makes  its  appearance 
soon  after  parturition,  and  con- 
tinues to  be  present  during  the 

HEPATIC  CELLS  containing  oil-globules.    Human,    involution   or  TCSOrption   of  the 

uterine  tissue. 

Source  of  Fat  in  the  Animal  Body.  —  It  is  evident  from  the  compo- 
sition of  many  nutritious  substances  consumed  by  man  and  animals 
that  a  considerable  quantity  of  fat  is  introduced  into  the  body  with 
the  food.  The  oleaginous  ingredients  of  the  cereal  grains,  of  nuts  and 
olives,  of  eggs,  milk,  and  meat,  show  that  both  animal  and  vegetable 
foods  contribute  a  certain  propor- 
tion of  fat  to  the  system.  But  it 
appears  that  fatty  substances  may 
also  be  formed  within  the  body, 
for  under  some  conditions  more 
fat  is  deposited  in  the  adipose 
tissue  and  elsewhere  than  can  be 
accounted  for  by  that  introduced 
during  the  same  time  with  the 
food.  This  fact  has  been  placed 
beyond  question  by  the  experi- 
ments of  Dumas  and  Milne 
Edwards  *  on  bees,  those  of 
Persoz  on  geese,  those  of  Bous- 
singault  f  on  geese,  ducks,  and 
pigs,  and  those  of  Lawes  and 
Gilbert  J  on  pigs. 
periments  the  amount  of  fat  in 
the  whole  body  was  first  ascertained  by  comparative  examination  of 
other  animals  in  the  same  condition.  The  subjects  of  the  experiment 

*Annales  de  Chim.  et  de  Phys.     3m'  S6rie.  torn.  XIV.,  pp.  400,  408. 

tChimic  A^ricole.     Paris,  1854. 

%  Philosophical  Magazine.     London,  1866.    Vol.  XXXIL,  p.  439. 


FIG.  9. 


In  these  ex-  MuscuLAB  FlBREasft^ 


three  week 


IIYDKOCARBONACEOUS    SUBSTANCES.  69 

were  then  kept  upon  a  definite  regimen,  in  which  the  quantity  of  fat  was 
determined  by  analysis.  This  was  continued  for  periods  varying  from 
one  to  eight  months,  after  which  the  animals  were  killed  and  their 
tissues  examined.  The  result  showed  that  considerably  more  fat  had 
accumulated  in  the  system  than  had  been  supplied  in  the  food.  Conse- 
quently, oleaginous  substances  must  in  some  cases,  and  perhaps  habitu- 
ally, be  formed  in  the  interior  of  the  body  by  transformation  of  other 
nutritive  materials.  There  is  no  discrepancy  among  observers  on  this 
point. 

As  for  the  special  materials  from  which  fat  is  thus  produced  in  the 
nimal  system,  its  most  probable  source  seems  to  be  the  carbo-hydrates, 
t  has  already  been  shown  (page  63,)  that  such  a  change  undoubtedly 
kes  place  in  vegetables ;  and  as  it  is  not  effected  in  plants,  so  far  as 
e  can  judge,  by  simple  deoxidation,  but  by  a  kind  of  process  which 
ay  also  take  place  in  animals,  there  is  no  reason  for  doubting  the 
ssibility  of  a  similar  transformation  in  the  interior  of  the  animal 
ody.     Other  considerations  make  it  highly  probable  or  certain.    Vege- 
table-feeding animals,  like  sheep  and  cows,  living  on  green  food  abound- 
ing in  carbo-hydrates,  will  often  accumulate  a  large  amount  of  fatty 
matter  in  the  system,  or  discharge  it  with  the  milk.     In  many  of  the 
experiments  just  quoted,  the  carbo-hydrates  preponderated  so  much  in 
the  food  supplied,  that  the  excess  of  fat  produced  during  the  observa- 
tion could  hardly  be  attributed  to  any  other  source.     And  finally,  it  is  a 
atter  of  common  experience  that  food  consisting  of  starchy  and  sac- 
harine  materials  is  especially  a  fattening  food,  both  for  the  domestic 
imals  and  for  man. 

But  these  substances  do  not  possess  in  themselves  the  requisite  con- 
ditions for  a  fatty  transformation ;  it  can  take  place  only  in  the  living 
ody.     As  the  deoxidation  of  carbonic  acid  and  water  by  plants  is 
ffected  under  the  influence  of  their  chlorophylle,  so  the  carbo-hydrates 
f  the  food  require  the  action  of  the  animal  tissues  for  their  conversion 
nto  fat.     This  explains  why  the  fat  production  varies  so  much  under 
e  same  diet  in  different  animals,  and  even  in  different  individuals  of 
he  human  species.     There  are  cases  of  hereditary  obesity,  coming  on 
t  the  same  period  of  life  in  the  children  as  in  the  parents,  irrespective 
great  measure  of  the  kind  of  food  employed ;  and  there  are  persons 
ho  seem  hardly  capable  of  taking  starchy  or  saccharine  substances 
without  converting  them  into  fat,  while  others  may  continue  a  mixed 
diet  indefinitely  without  increasing  their  adipose  tissue. 

It  is  not  unlikely  that  fat  may  also  be  formed  from  the  albuminous 
matters  of  the  food,  though  the  evidence  of  this  is  less  satisfactory  than 
the  case  of  the  carbo-hydrates.  Carnivorous  animals,  as  a  rule,  have 
less  fat  than  the  herbivora  ;  and,  among  men,  those  who  habitually  con- 
sume a  large  proportion  of  meat  are  less  liable  to  obesity  than  those 
living  mainly  on  vegetable  food.  Nevertheless,  it  is  believed  by  many 
that  fat  is  sometimes  the  result  of  a  partial  decomposition  of  albu- 
minous matters.  In  this  case,  the  production  of  fat  must  be  accom- 


70  PHYSIOLOGICAL    CHEMISTRY. 

panied  by  the  liberation  of  another  substance  containing  nitrogen,  which 
is  an  element  in  the  composition  of  albumen.  We  know  that  this  actu- 
ally occurs  in  the  living  body,  and  that  such  a  nitrogenous  substance 
(urea)  is  discharged  with  the  urine.  Still  this  only  gives  a  possi- 
bility, but  not  a  proof,  that  the  other  product  of  decomposition  is  a  fat. 
Furthermore,  the  appearance  of  fat  in  isolated  drops  and  granules,  in 
the  substance  of  glandular  cells  or  degenerating  muscular  fibres,  of 
which  we  know  so  many  instances,  has  been  regarded  as  an  indication 
that  the  fatty  material  in  these  cases  is  formed  on  the  spot  from  the 
albuminous  substance  in  which  it  is  imbedded.  But  it  is  evident  that 
the  substance  of  the  cell  or  muscular  fibre  is  permeable  to  serous  fluids 
containing  saccharine  ingredients,  and  that  these  may  have  been  the 
immediate  source  of  the  fatty  deposit.  Most  of  the  other  reasons 
adduced  in  favor  of  the  production  of  fat  from  albuminous  matters 
are  open  to  similar  objections.  On  the  whole,  it  may  be  said,  that 
while  we  have  no  reason  to  discredit  the  possibility  of  a  fatty  trans- 
formation of  albuminous  matters,  the  main  source  of  oleaginous  sub- 
stances, in  point  of  fact,  over  and  above  those  contained  in  the  food,  is 
to  be  found  in  the  carbo-hydrates. 

Physiological  Relations  of  Fat. — The  fatty  substances  of  the  body 
are  subservient  to  a  variety  of  uses.  Some  of  these  uses  are  of  a  physi- 
cal character,  while  others  imply  chemical  changes  which  are  evidently 
of  the  first  importance  in  nutrition,  though  as  yet  unknown  in  their 
details.  The  first  and  most  palpable  function  of  the  adipose  tissue  is  a 
mechanical  one.  It  acts  as  a  cushion  to  protect  the  neighboring-  parts 
from  injury,  and  to  facilitate  the  movement  of  muscular  organs.  The 
adipose  layer  in  the  subcutaneous  tissue,  in  the  soles  of  the  feet  and 
the  palms  of  the  hands,  between  the  voluntary  muscles,  about  the  eyeball 
at  the  fundus  of  the  orbit,  and  about  the  heart  at  the  origin  of  the  great 
vessels,  is  mainly  useful  in  this  way.  The  plicae  adipose  of  the  artic- 
ular cavities  have  a  similar  mechanical  function,  and  the  sebaceous 
secretion  of  the  cutaneous  glandules,  by  its  oleaginous  properties,  pro- 
tects the  skin  and  hair  from  desiccation  and  preserves  their  pliability. 
The  fatty  tissue  is  also  important  as  a  non-conductor  of  heat.  It 
envelops  the  subcutaneous  parts  like  a  blanket,  and  retains  in  the 
system  much  of  the  animal  heat  which  would  otherwise  be  dissipated. 
Its  deposit  in  certain  localities,  as  in  the  omentum,  has  no  doubt  a 
special  reference  to  the  protection,  in  this  respect,  of  the  underlying 
organs.  In  all  these  situations,  however,  the  fat  is  an  indifferent  body 
in  its  chemical  relations.  Throughout  the  system,  wherever  fat  can  lie 
recognized  by  the  microscope  in  the  form  of  distinct  drops  or  globules, 
it  is  evidently,  for  the  time  being,  in  a  state  of  physiological  inactivity, 
being  transported  by  the  circulating  fluids  or  retained  on  the  spot 
nutriment  of  reserve.  In  certain  parts,  where  it  is  very  abundant,  as 
in  the  marrow  of  the  long  bones,  we  can  hardly  attribute  to  it  any 
further  value  than  this.  But  it  has  also  other  functions  immediately 
connected  with  the  renovation  of  the  tissues.  This  is  shown  by  the 


HYDROCARBONACEOUS  SUBSTANCES. 


71 


fact  that  it  is  often  taken  with  the  food  in  noticeable  quantity  and 
consumed  in  the  body,  without  any  increase  of  the  internal  adipose 
deposit.  In  cases  of  acute  wasting  disease,  of  temporary  abstinence, 
and  in  the  hibernation  of  animals,  the  fat  previously  stored  up  greatly 
diminishes  or  disappears  altogether.  In  these  instances  the  oleaginous 
matter  which  disappears  from  the  body  is  not  to  be  found  in  the  excre- 
tions. The  sebaceous  secretion  of  the  skin  is  the  only  form  of  fatty 
matter  discharged  externally,  and  this  is  far  inferior  in  quantity  to 
that  taken  with  the  food  and  consumed  by  the  system.  The  fat  which 
thus  disappears  is  therefore  disposed  of  by  decomposition  in  the  body. 
We  cannot  follow  with  any  certainty  the  steps  of  this  decomposition, 
nor  determine  the  successive  alterations  which  take  place  in  the  fatty 
substance  during  its  passage  through  the  system.  But  it  undergoes 
changes  of  some  kind  by  which  its  essential  characters  are  lost,  and 
its  elements  are  finally  discharged  under  another  form,  in  the  products 
of  excretion. 

Cholesterine,  C26H440, 

So  called  from  its  occurring  as  a  solid  deposit  from  the  bile,  in  which 
form  it  was  first  discovered.  It  is  included  in  the  present  group  of 
organic  compounds,  owing  to  its  being  crystallizable  and  non-nitroge- 
nous. But  it  has  no  real  affinity  with  the  fatty  matters,  although  it 
resembles  them  in  certain  physical  properties,  such  as  its  insolubility 
in  water,  and  its  solubility  in  ether,  boiling  alcohol,  chloroform,  oily 
liquids,  and  solutions  of  the  biliary  salts.  It  is  incapable  of  saponifi- 
cation,  and  at  a  high  temperature  (360°  C.)  may  be  volatilized  without 
decomposition.  Its  solutions  rotate  the  plane  of  polarization  to  the  left 
32°.  It  is  deposited  from  its 

alcoholic  or  ethereal  solution  in  FIG.  10. 

the  form  of  thin,  colorless,  trans- 
parent, rhomboidal  plates,  por- 
tions of  which  are  often  cut  out 
by  lines  of  cleavage  parallel  to 
the  edges  of  the  crystal.  They 
frequently  occur  deposited  in 
layers,  in  which  the  outlines  of 
the  subjacent  crystals  show  very 
distinctly  through  the  substance 
of  those  above.  If  the  crystals 
be  treated  with  a  mixture  of  1 
volume  of  water  and  5  volumes 
of  sulphuric  acid,  and  gently 
warmed,  their  borders  take  a 
bright  carmine  color,  changing 
afterward  to  violet .  (Gorup- 
Besanez.) 

If  triturated  with  strong  sulphuric  acid,  they  yield,  on  the  addition 
of  chloroform,  a  blood-red  color,  which  afterward  disappears  by  expo- 


CHOLESTERINE,  from  the  contents  of  an  encysted 
tumor. 


72  PHYSIOLOGICAL    CHEMISTRY. 

sure,  passing  gradually  from  red  to  violet,  blue,  and  green,  the  liquid 
finally  becoming  colorless.  (Hoppe-Seyler.) 

Cholesterine  is  a  constant  ingredient  of  the  bile,  in  which  it  occurs 
in  the  proportion  of  0.5  part  per  thousand,  and  which  seems  to  be  its 
principal  channel  of  exit  from  the  system.  It  is  also  present  in  the 
sebaceous  matter  of  the  skin,  and  appears  in  considerable  quantity  in 
accidental  deposits  or  exudations,  such  as  biliary  calculi,  the  fluid  of 
hydrocele,  and  the  contents  of  various  encysted  tumors.  It  exists  in 
the  blood,  the  liver,  the  spleen,  the  crystalline  lens,  and  especially 
in  the  nerves,  spinal  cord,  and  brain,  in  which  last  it  has  been  found 
by  Flint*  in  the  proportion  of  about  one  part  per  thousand.  It  is  also 
present  in  the  yolk  of  egg,  and  in  the  spermatozoa  of  all  the  higher 
and  lower  animals,  f  It  is  not  confined  to  the  animal  body,  but  is  found 
in  many  vegetable  structures,  such  as  wheat,  Indian  corn,  peas  and  beans, 
olives,  almonds,  young  buds,  and  mould-fungi. 

The  physiological  relations  of  cholesterine  are  very  obscure,  as  com- 
pared with  those  of  true  fatty  substances.  Notwithstanding  its  wide 
distribution  in  the  animal  system,  in  nutritious  substances,  in  the  blood, 
and  in  such  important  organs  as  the  brain  and  nerves,  it  is  mostly  re- 
garded as  a  product  of  decomposition  of  their  organic  ingredients,  rather 
than  as  serving  for  the  nutrition  of  the  tissues.  But  from  what  sub- 
stance it  is  derived,  or  in  what  way  it  is  produced,  is  at  present  unknown. 
It  seems  to  be,  without  doubt,  absorbed  from  the  substance  of  the  nervous 
system  by  the  blood,  transported  in  this  way  to  the  liver,  and  thence 
discharged  with  the  bile  into  the  alimentary  canal.  In  the  observations 
of  Flint,*  its  quantity  in  the  blood  of  the  dog  was  found  to  incn-a  si- 
while  passing  through  the  brain,  from  0.52  to  1.09  per  thousand  parts. 
Its  presence  in  the  blood,  as  a  product  of  organic  disintegration,  would 
explain  its  frequent  occurrence  in  exudations  and  morbid  deposits  in 
different  parts  of  the  body.  According  to  most  observers  (Lehmann, 
Gorup-Besanez,  Hoppe-Seyler)  it  is  a  normal  ingredient  of  the  feces, 
as  well  as  of  the  sebaceous  matter,  and  is  therefore  either  wholly  or 
partly  discharged  from  the  body  under  its  own  form. 

*  American  Journal  of  the  Medical  Sciences.     Philadelphia,  October,  1862. 
f  Hoppe-Seyler.    Physiologische  Chemie.    Berlin,  1877,  p.  81. 


CHAPTER  IV. 
ALBUMENOID  SUBSTANCES. 

THE  albumenoid  substances  as  a  class  occupy  the  first  place  in  im- 
portance in  the  living  body.  Their  wide  distribution,  their 
ibundant  quantity,  and  the  part  which  they  take  in  the  vital  operations 
idicate  a  marked  distinction  between  them  and  all  other  ingredients  of 
ic  organized  frame.  They  are  derived  both  from  animal  and  vege- 
table sources,  and  none  of  the  nutritious  juices  in  either  kingdom  is 
without  them.  But  in  plants,  as  a  rule,  the  albumenoid  substances  are 
in  comparatively  small  quantity,  while  in  man  and  animals  they  are 
by  far  the  largest  part  of  the  solid  constituents  of  the  body,  and  with 
the  exception  of  water  are  more  abundant  than  any  other  of  its  ingre- 
dients. In  the  blood  and  muscles  they  form  nearly  20  per  cent,  of  the 
whole  mass,  and  in  the  bones  and  cartilages  from  30  to  40  per  cent. 
[any  of  them  have  special  forms  of  activity  which  distinguish  them 
from  all  other  organic  substances ;  and  everywhere  their  chemical  con- 
stitution, their  physical  characters,  and  their  physiological  properties 
show  them  to  be  directly  connected  with  the  active  phenomena  of 
life. 

General  Characters  of  the  Albumenoid  Substances. — The  first  im- 
portant feature  of  these  substances  is  that  they  contain  nitrogen  as  one 
of  their  constituent  elements.  This  at  once  distinguishes  them  from 
the  preceding  group,  and  gives  them  a  different  place  as  ingredients  of 
the  food.  The  quantity  of  nitrogen  present  varies  from  about  14  to  18 
per  cent,  of  their  weight.  Most  of  them  contain  also  a  small  quantity 
of  sulphur,  and  nearly  all,  when  incinerated,  leave  a  minute  residue  of 
lime  phosphate,  from  which  they  cannot  be  entirely  freed  by  the  usual 
means  of  purification.  Their  average  composition  by  weight,  accord- 
ing to  the  tables  of  Hoppe-Seyler,  Wurtz,  and  Gorup-Besanez,  is  as 
follows : 

AVEEAGE  COMPOSITION  OF  ALBUMENOID  SUBSTANCES. 

Carbon 52.8 

Hydrogen    . 7.1 

Nitrogen 16.6 

Oxygen 22.1 

Sulphur 1.4 

1000 

Their  exact  chemical  structure  has  not  been  determined  with  cer- 

73 


74  PHYSIOLOGICAL    CHEMISTRY. 

tainty  in  any  case.  Owing  to  the  difficulty  of  obtaining  them  in  a 
state  of  absolute  purity,  the  uncertainty  whether  their  sulphur  is  an 
essential  constituent  element  or  only  an  incidental  ingredient,  and  par- 
ticularly owing  to  the  number  and  variety  of  the  products  of  their  artifi- 
cial decomposition,  their  atomic  constitution  is  still  a  matter  of  doubt. 
The  formula  for  albumen  which  was  proposed  by  Lieberkiihn,  and 
adopted  by  Johnson  and  Schiitzenberger,*  is  as  follows : 

Albumen;  C72H112]Sri8O22S. 

But  although  this  formula  has  been  shown  to  account  in  a  satisfac- 
tory manner  for  certain  combinations  and  decompositions,  it  has  not 
been  generally  accepted ;  and  in  the  opinion  of  most  chemists,  the 
manner  in  which  the  elements  of  these  substances  are  combined  is 
entirely  unknown. 

The  albumenoid  matters  are  not  crystallizable.  They  always,  when 
pure,  assume  an  amorphous  condition,  in  which  they  are  sometimes 
solid,  as  in  the  bones ;  sometimes  fluid,  as  in  the  plasma  of  the  blood  ; 
and  sometimes  semi-solid,  as  in  the  muscles  and  the  glandular  organs. 
Even  in  the  fluids,  when  present  in  considerable  quantity,  as  in  the 
blood-plasma,  the  pancreatic  juice,  or  the  submaxillary  saliva,  they  give 
to  the  solution  a  viscid  or  mucilaginous  consistency,  which  is  more 
marked  in  proportion  to  their  abundance. 

Some  of  them  are  soluble  in  water,  others  in  solutions  of  the  neu- 
tral salts  in  different  degrees  of  concentration.  Some  of  them  may 
be  extracted  from  the  solid  tissues  by  water  at  a  boiling  temperature, 
and  a  few  resist  the  action  of  all  solvent  fluids.  When  in  solution 
they  all  rotate  the  plane  of  polarization  toward  the  left.  They  are  all 
hygroscopic.  When  dried  by  evaporation,  and  afterward  brought  in 
contact  with  water,  they  absorb  it  with  readiness,  becoming  swollen 
and  assuming  a  more  or  less  softened,  gelatinous,  mucous,  or  fluid  con- 
sistency, according  to  the  quantity  of  water  with  which  they  A 
originally  associated.  When  subjected  to  artificial  decomposition  by 
heat  and  a  caustic  alkali,  they  yield  a  great  variety  of  gaseous  and 
crystalline  substances,  among  which  carbonic  acid  and  ammonia  are 
constantly  present  in  the  proportion  of  2  to  l.f  Oxalic  acid  and  sul- 
phurous acid  are  also  given  off  as  products  of  decomposition. 

The  albumenoid  substances  are  not  diffusible;  that  is,  they  do  not 
readily  pass,  in  solution,  through  parchment  paper  or  animal  mem- 
branes. This  character  is  probably  connected  with  their  amorphous 
and  uncrystallizable  condition  ;  and  they  are  distinguished  by  it  in  a 
marked  degree  from  mineral  salts  and  crystallizable  organic  substances, 
which  pass  through  such  membranes  by  diffusion  with  i^reat  facility. 
It  is  frequently  resorted  to  as  a  means  for  the  purification  of  albume- 


*\Vurt/-.      Chimie  Biolo^i-n^,   Paris,  1SSO,  pp.  »>:, 

f  (iorup-Bcsanez.     Lehrbuch   dor  Phjuologfohen  Ghemie,  Braunschweig,  1878, 
p.  114. 


= 


ALBTJMENOID    SUBSTANCES.  75 

noid  substances  from  other  matters  with  which  they  are  mingled. 
Thus  if  a  solution  containing  albumen,  glucose,  and  sodium  chloride 
be  immersed  in  a  vessel  of  pure  water,  with  a  partition  of  parchment 
paper  between  the  two  liquids,  the  glucose  and  the  salt  will  pass 
through  the  membrane  and  become  diffused  in  the  water,  while  the 
albumen  will  remain  behind.  By  renewing  the  water  in  the  exte- 
rior vessel  and  thus  keeping  up  the  activity  of  diffusion,  nearly 
the  whole  of  the  glucose  and  the  salt  may  be  removed  from  the 
interior  solution,  and  the  albumen  left  in  a  purified  condition.  This 
method  is  termed  "  dialysis,"  and  is  frequently  employed  for  obtain- 
ing albumenoid  matters  free  from  admixture  with  other  substances. 
There  is  one  remarkable  exception,  among  the  albumenoids,  to  the  rule 

f  non-diffusibility.  It  is  that  of  "  peptone,"  the  substance  produced 
from  albuminous  matters  by  digestion,  which  retains  all  their  other 
essential  properties,  but  has  acquired  the  power  of  passing  by  diffu- 
sion through  animal  membranes.  It  is  thus  rendered  capable  of 
being  absorbed  by  the  intestine,  and  of  entering  the  current  of  the 
circulation. 

The  albumenoid  substances  are  coagulable.  This  property  consists 
in  their  capacity,  when  fluid,  of  suddenly  changing,  under  certain  phys- 
ical or  chemical  influences,  to  the  solid  form ;  so  that  they  either  sepa- 
rate from  the  other  ingredients  of  the  liquid,  or  convert  the  whole  into 
a  gelatinous  mass.  This  difference  depends  on  the  relative  quantity  in 
which  they  are  present,  and  on  the  manner  in  which  they  are  associ- 
ated with  the  other  ingredients.  Thus  if  a  specimen  of  slightly 
albuminous  urine  be  heated,  the  albuminous  matter  is  thrown  down 
as  a  flaky  deposit,  while  the  rest  remains  liquid ;  but  if  the  serum 
of  blood  be  treated  in  the  same  way  it  solidifies  into  a  uniform 
mass.  In  neither  case  is  the  process  of  coagulation  a  simple  precipita- 
tion, as  where  a  mineral  salt  is  thrown  down  from  solution  in  a  fluid. 
The  albumenoid  substance,  when  coagulated,  still  retains  its  normal  pro- 
portion of  water,  and  in  the  instance  of  the  serum  of  blood,  it  holds 
the  whole  of  the  water  present,  so  that  no  liquid  separates  from  the 

agulum.  It  may  be  driven  off  by  evaporation,  but  the  coagulated 
albuminous  matter  is  still  hygroscopic,  and  will  again  take  up  water  by 
absorption  to  the  same  extent  as  before.  A  coagulated  substance  is 
usually  permanently  altered  in  character,  and  cannot  be  restored  to 
fluidity  except  by  means  of  acid  or  alkaline  solvents,  which  still  further 
modify  its  original  properties. 

Different  albumenoid  matters  are  coagulated  by  different  agents,  and 
these  reactions  form  a  convenient  and  sometimes  the  principal  test  by 
which  they  are  distinguished.  Thus  albumen  is  coagulated  by  heat 
or  the  mineral  acids,  but  not  by  organic  acids.  Caseine,  the  albumi- 
nous ingredient  of  milk,  is  coagulated  by  either  mineral  or  organic 
acids,  but  not  by  heat.  The  animal  matter  of  the  pancreatic  juice  is 
coagulated  by  heat  or  the  mineral  acids ;  but  also  by  magnesium  sul- 
phate, which  does  not  affect  albumen.  The  coagulation  of  some  albu- 


76  PHYSIOLOGICAL    CHEMISTRY. 

menoid  matters  is  caused  by  the  action  of  ferments,  which  are  without 
influence  on  the  remainder.  The  exact  nature  of  the  change  which 
takes  place  in  coagulation  has  not  been  determined,  and  it  probably 
cannot  be  successfully  investigated  until  the  real  constitution  of  the 
albumenoid  substances  is  known. 

Another  important  feature  of  the  albumenoid  substances  is  their  con- 
nection with  "catalyses"  or  "catalytic  transformations."  These  are 
chemical  changes,  either  combinations  or  decompositions,  which  take 
place  under  the  influence  of  a  body  acting  in  a  hitherto  unexplained 
way,  apparently  by  mere  contact  and  without  being  itself  either 
decomposed  or  combined.  Such  a  body  is  a  ferment.  It  produces  its 
effect  in  very  small  quantity ;  and  it  may  cause  important  transfor- 
mations in  a  large  amount  of  other  material  without  its  own  substance 
being  perceptibly  diminished.  Thus  the  starchy  matter  of  plants  is 
converted  into  glucose  by  the  influence  of  a  nitrogenous  body  termed 
"diastase;"  and  according  to  Pay  en,*  one  part  of  diastase  is  capable 
of  converting  into  glucose  2,000  parts  of  starch.  All  the  ferments 
belong  to  the  class  of  albumenoid  substances.  Many  of  these  sub- 
stances are  themselves  liable  to  catalytic  transformation  under  the 
influence  of  ferments.  Such  transformations  are  certainly  the  principal 
acts  in  the  digestion  and  assimilation  of  food ;  and  changes  of  a 
similar  kind  are  so  general  and  so  important  throughout  the  body 
that  some  physiologists  are  inclined  to  attribute  to  their  influence 
all  the  essential  phenomena  of  nutrition  and  waste.  Each  ferment 
operates  with  the  greatest  vigor  under  certain  special  conditions ;  as, 
for  example,  an  acid,  neutral  or  alkaline  medium,  the  presence  or 
absence  of  a  saline  solution,  or  a  slightly  higher  or  lower  tempera- 
ture; but  they  are  all  arrested  by  the  strong  acids  or  alkalies,  by 
concentrated  saline  solutions,  by  the  absence  of  moisture,  or  by  a  boil- 
ing or  freezing  temperature.  The  most  favorable  temperature  is 
usually  about  that  of  the  living  body. 

At  a  temperature  of  300°  C.  or  over,  the  albumenoid  substances  are 
decomposed  into  gaseous  products.  But  if  subjected  for  a  certain  time 
to  a  temperature  of  about  125°  C.,  they  undergo  a  change  by  which  a 
peculiarly  agreeable  flavor  is  developed,  and  by  which  many  of  them 
become  suitable  for  human  food.  It  is  this  flavor  which  is  produced 
in  the  process  of  cooking,  and  which  always  depends  upon  the  pres- 
ence of  a  certain  quantity  of  albumenoid  matter  in  the  substance 
employed.  If  the  temperature  at  which  the  cooking  process  is  carried 
on  be  too  low,  the  characteristic  flavors  are  not  developed ;  if  it  be  too 
high,  they  are  destroyed  and  replaced  by  empyreuniutic  odors,  from 
the  combustion  or  decomposition  of  the  ingredients  of  the  food. 

Lastly,  the  albumenoid  substances  are  distinguished  by  the  prop 
of  putrefaction.     This  is  a  process  in  which  dead  animal  substniuvs, 
when  exposed  to  the  atmosphere  at  a  moderately  warm  temperature, 

*  Substances  Alimentaires,  Paris,  1865,  p.  5. 


ALBUMENOID    SUBSTANCES.  77 

soften,  liquefy,  and  are  finally  decomposed,  with  the  production  of 
certain  fetid  gases,  among  which  are  hydrogen  sulphide  and  carbide, 
usually  with  more  or  less  carbonic  acid,  nitrogen,  and  ammonia.  These 
emanations  cause  an  odor  which  is  easily  recognized  as  "  putrefac- 
tive ; "  and  no  substance  is  capable  of  putrefaction,  unless  it  contain 
albumenoid  matters  among  its  ingredients.  As  these  matters  are 
more  abundant  in  animals  than  in  vegetables,  the  phenomena  of 
putrefaction  are  most  distinctly  marked  in  the  decay  of  animal  tissues. 
But  they  will  take  place  in  both,  under  the  requisite  conditions.  The 
rapidity  of  putrefaction  in  animal  substances  varies  with  their  con- 
sistency ;  the  liquids  and  the  soft  parts  undergoing  this  change  more 
readily  than  those  of  firmer  texture.  In  some  which  are  exceedingly 
dense,  like  the  bones,  cartilages,  hair,  and  elastic  tissues,  desiccation 
may  take  place  before  putrefaction  can  be  established ;  but  if  their 
animal  matter  be  extracted  in  the  form  of  gelatine  or  otherwise,  and 
kept  for  a  short  time  in  the  moist  condition,  it  will  putrefy  like  any 
other  albumenoid  substance. 

In  order  that  putrefaction  may  take  place,  certain  conditions  are 
necessary.  In  the  first  place,  it  requires  the  access  of  atmospheric  air, 
or  of  some  fluid  containing  oxygen.  If  the  putrescible  substance  be 
boiled,  so  as  to  expel  all  the  free  oxygen  contained  in  its  fluids,  and 
inclosed  in  a  hermetically  sealed  vessel,  no  putrefaction  takes  place, 
and  the  substance  remains  unaltered  indefinitely.  It  is  by  this  means 
that  cooked  meats  are  preserved  in  cans,  for  use  upon  long  voyages 
r  expeditions.  So  long  as  the  cans  are  kept  perfectly  closed,  their 

ntents  remain  sound.     After  they  are  opened  and  the  air  admitted  to 
heir  interior,  the  food  must  be  used  at  once,  otherwise  it  will  putrefy 

a  short  time. 

Another  essential  condition  for  putrefaction  is  the  presence  of  moist- 
re.  Albumenoid  substances  in  a  perfectly  dry  state  do  not  undergo 
decomposition ;  and  in  some  regions,  where  a  high  temperature  and 
a  dry  atmosphere  favor  their  rapid  desiccation,  this  fact  is  utilized  for 
the  preservation  of  meats.  Immediately  after  the  animal  is  killed,  the 
flesh  is  cut  into  strips  and  dried  in  the  air ;  and  desiccation  being  thus 
completed  before  putrefaction  has  commenced,  the  food  is  preserved  for 
future  use. 

The  third  requisite  for  putrefaction  is  a  moderately  elevated  temper- 
ature. It  goes  on  most  rapidly  between  25°  and  35°  C.  Below  25° 
it  gradually  diminishes  in  activity,  and  ceases  altogether  about  the 
freezing  point  of  water.  Meats,  therefore,  which  are  kept  at  a  suffi- 
iently  low  temperature  do  not  putrefy.  The  carcass  of  an  extinct 
mammoth  has  even  been  found  imbedded  in  ice  in  Northern  Siberia, 
in  such  a  state  of  preservation  that  its  flesh  was  devoured  by  dogs 
and  other  animals.*  A  temperature  much  above  35°  is  also  unfavor- 

*Meinoires  de  1'Academie  Imperiale  des  Sciences  de  St.  Petersbourg,  tome  5,  p. 
440. 


78 


PHYSIOLOGICAL    CHEMISTRY. 


FlG.  11. 


CELLS  OF  BACTERIUM  TERMO  ;  from  a  putrefying 
infusion. 


able  to  the  putrefactive  change,  and  it  is  completely  arrested  by  a  heat 
approaching  that  of  boiling  water. 

The  process  of  putrefaction 
is  accomplished  by  the  growth 
and  multiplication  of  a  micro- 
scopic vegetable  organism, 
somewhat  analogous  to  that 
causing  the  alcoholic  fermen- 
tation in  saccharine  liquids. 
If  any  clear  solution  con- 
taining animal  or  vegetable 
albumenoid  matters  be  ex- 
posed to  the  air  at  a  moder- 
ate temperature,  after  a  short 
time  it  becomes  turbid.  This 
turbidity  is  due  to  the  devel- 
opment of  minute  vegetable 
cells,  of  very  simple  organi- 
zation, which  rapidly  multi- 
ply in  the  decomposing  li- 
quid. The  cells  belong  to 
the  genus  "  Bacterium,"  so  called  from  their  rod-like  form ;  and  the 
species  found  in  putrefying  infusions  is  known  by  the  name  of  Bacte- 
rium termo.  The  cells  are  of  an  oblong  form,  about  3  mmm.  in 
length  by  0.6  mmm.  in  thickness.  They  usually  appear  double,  each 
pair  consisting  of  cells  placed  end  to  end.  This  appearance  is  due 
to  their  multiplication  by  spontaneous  division  of  the  growing  cell. 
After  a  time  the  two  cells,  thus  formed  out  of  a  single  one,  separate 
from  each  other,  and  each  repeats  the  process  for  itself. 

One  of  the  most  remarkable  characters  of  bacterium  cells  is  their 
movement.  During  a  certain  period  of  their  development  they 
exhibit  an  incessant  motion,  consisting  in  a  conical  rotation  about 
their  longitudinal  axis,  by  which  they  are  transported  in  various  direc- 
tions. This  motion  is  often  so  rapid  that  it  can  hardly  be  followed 
by  the  eye ;  in  other  instances  it  is  so  slow  that  its  mechanism  may  be 
distinguished.  The  movement  and  multiplication  of  the  cells  go  on 
while  putrefaction  continues.  When  all  the  albumenoid  ingredients 
of  the  infusion  have  been  decomposed,  the  liquid  again  becomes  clear, 
and  the  bacterium  cells  subside  to  the  bottom  in  a  quiescent  layer. 
But  a  small  portion  of  this  layer  will  readily  excite  putrefaction  in 
another  albuminous  liquid. 

As  the  bacterium  cells  effect  the  decomposition  of  albumenoid  matters 
by  means  of  their  vegetative  activity,  putrefaction  is  limited  by  tin- 
same  conditions.  Bacteria  belong  to  the  group  of  colorless  crypto- 
gamic  plants.  Like  other  plants  of  this  kind,  they  assimilate  organic 
substances  ready  formed,  at  the  same  time  absorbing  oxygen  and  ex- 
haling carbonic  acid,  after  the  manner  of  animals. 


ALBUMENOID    SUBSTANCES.  79 

As  oxygen  therefore  is  essential  to  their  growth,  its  presence  is  also 
necessary  for  putrefaction.  Furthermore,  as  no  plants  can  grow  with- 
out moisture,  and  as  they  require  a  temperature  of  moderate  warmth, 
putrefaction  must  also  be  suspended  both  by  desiccation  and  by  exces- 
sive cold  or  heat. 

Fermentation  and  putrefaction,  accordingly,  are  analogous  processes, 
going  on  under  the  influence  of  different  microscopic  vegetations.  The 
former  takes  place  in  saccharine  liquids,  the  latter  in  those  containing 
albumenoid  matter  ;  since  the  yeast-plant  requires  for  its  growth  a  pre- 
ponderance of  carbo-hydrates,  while  bacterium  cells  are  nourished  by 
the  absorption  of  nitrogenous  matter. 

Origin  of  the  Albumenoid  Substances. — Albumenoid   matters   are 

!  first  produced  in  the  vegetable  world  by  assimilation  of  nitrogen  with 
the  carbo-hydrates.  This  is  proved  by  the  fact  that  green  plants  which 
can  produce  starch  and  sugar  from  carbonic  acid  and  water,  if  supplied 
with  moisture  containing  nitrogenous  salts,  will  thrive  vigorously  and 
increase  many  fold  their  contents  of  albuminous  matter.*  The  pro- 
duction of  this  new  material  will  take  place  in  other  parts  of  the  plant 
beside  the  leaves,  provided  there  be  present  saccharine  juices  already 
formed  and  nitrogen  compounds  fit  for  absorption.  Furthermore,  color- 
less plants,  which  cannot  produce  starch  or  sugar  for  themselves,  if 
nourished  with  saccharine  solutions  and  inorganic  nitrogen  compounds, 
ill  also  largely  increase  the  mass  of  their  albumenoid  ingredients. 
It  appears  that  the  nitrogen  thus  assimilated  by  plants  is  not  absorbed 
n  a  free  state.  Notwithstanding  the  abundant  quantity  of  this  element 
in  the  air,  it  is  accepted  by  vegetable  physiologists,  as  the  result  of 
decisive  investigations,  that  the  free  atmospheric  nitrogen  is  not  avail- 
able for  vegetation. f  Plants  appropriate  their  nitrogen,  both  from  the 
atmosphere  and  the  soil,  in  the  form  of  nitrates  and  ammonium  salts, 
which  are  absorbed  by  the  roots,  taken  up  by  the  vegetable  juices,  and 
thus  serve  for  the  production  of  albumenoid  substances.  The  sulphur 
requisite  for  these  matters  is  taken  up  in  the  form  of  sulphates,  which 
are  afterward  decomposed  in  the  vegetable  juices. 

Classification  of  the  Albumenoid  Substances. — The  arrangement  of 
these  matters  in  groups,  according  to  appropriate  generic  characters,  is 
necessary  to  facilitate  their  study  and  description.  Attempts  at  such 
a  classification,  based  upon  their  intimate  chemical  structure,  must  be 
futile,  so  long  as  we  are  destitute  of  certain  knowledge  in  this  respect. 
Even  their  characters  of  solubility  in  water,  dilute  acids  or  alkalies,  or 
saline  solutions,  vary  in  different  cases  by  such  slight  gradations  that 
they  can  only  be  considered  as  convenient  methods  of  diagnosis  rather 
than  as  positive  distinctions.  Their  treatment  by  stronger  reagents 
yields  substances  which  may  be  of  interest  for  theoretical  chemistry, 
but  which  are  not  to  be  found  in  the  living  body,  and  have  no  physio- 

*  Mayer,  Lehrbuch  der  Agrikultur-Chemie,  Heidelberg,  1871,  Band  i.  pp.  145, 150. 
f  Hoppe-Seyler,  Physiologische  Chemie.     Berlin,  1877,  p.  48. 


80  PHYSIOLOGICAL    CHEMISTRY. 

logical  value.  The  most  serviceable  arrangement  for  the  study  of 
these  substances,  as  materials  of  the  organized  fabric,  should  include 
their  simplest  and  most  easily  recognized  physical  characters,  the  forms 
under  which  they  occur  in  the  animal  frame,  and  the  part  which  they 
play  in  its  vital  operations.  For  this  purpose  they  may  be  divided,  as 
follows,  into  three  principal  groups. 

ALBUMINOUS  MATTERS. 

These  are  the  substances  which  naturally  stand  at  the  head  of  the 
albumenoid  class.  They  were,  many  years  ago,  called  "  proteine-com- 
pounds,"  because  Mulder,  according  to  a  view  now  abandoned,  consid- 
ered them  as  so  many  combinations  of  the  same  primitive  body, 
11  proteine,"  with  varying  proportions  of  sulphur  and  phosphorus. 
They  are  still  designated  by  some  writers  as  "proteids."  They  are  all 
abundant  ingredients  of  the  nutritive  juices,  and  their  especial  office  in 
the  living  body  seems  to  be  the  supply  of  material  for  the  nourishment 
of  the  permanent  structures.  They  include  the  following: 

1,  Albumen  of  Blood. 

This  substance,  also  called  Serum-albumen  or  Serine,  is  the  most 
abundant  organic  ingredient  of  the  blood-plasma,  where  it  exists  in  the 
proportion  of  53  parts  per  thousand.  After  spontaneous  coagulation 
of  the  blood,  and  separation  of  the  clot  and  serum,  it  remains  fluid  in 
the  serum.  It  is  also  found  in  the  lymph,  the  chyle,  the  pericardial 
fluid,  and  in  many  pathological  serous  exudations.  It  is  obtained  from 
dilute  serum  by  precipitating  other  albumenoid  ingredients  with  acetic 
or  carbonic  acid,  evaporating  the  filtered  fluid  to  dryness,  dissolving  in 
water,  and  lastly  removing  its  saline  substances  by  the  process  of 
dialysis  (page  75).  Serum-albumen  is  soluble  in  water  and  in  solu- 
tions of  the  neutral  salts,  from  which  it  is  not  precipitated  by  either 
dilute  alkalies  or  organic  acids.  Its  watery  solution  is  neutral  in  re- 
action, and  rotates  the  plane  of  polarization  toward  the  left  56°.  It  is 
coagulated  by  heat  (T2°  C.),  by  the  mineral  acids,  the  metallic  salts,  and 
especially  by  potassium  ferrocyanide  in  acidulated  solution,  which  is 
the  most  delicate  known  test  of  its  presence.  It  is  coagulated  by 
alcohol  in  excess,  but  not  by  ether.  Its  coagula  are  redissolved  by 
the  caustic  alkalies. 

2.  Egg-albumen. 

This  is  the  main  ingredient  in  the  white  of  egg.  It  was  the  earliest 
studied  of  all  the  albumenoid  matters,  and  received  its  name  from  the 
fact  of  its  turning  white  and  opaque  when  boiled.  It  is  an  important 
article  of  food,  and  supplies  most  of  the  albumenoid  matter  for  the 
nourishment  of  the  embryo  chick  during  incubation.  It  is  soluble  in 
water  and  in  neutral  saline  solutions.  Its  specific  power  of  rotation 
for  polarized  light  is  35.5°.  Like  serum-albumen,  it  is  coagulated  by 
heat,  alcohol,  mineral  acids,  metallic  salts,  and  potassium  ferrocyanide 
in  acidulated  solution ;  but  it  is  also  thrown  down  by  agitation  with 
ether,  which  does  not  affect  the  preceding  variety. 


ALBUMENOID    SUBSTANCES.  81 

3.  Caseine. 

Caseine  is  the  albuminous  matter  of  milk,  where  it  is  present  in  the 
proportion  of  a  little  more  than  40  parts  per  thousand.  It  is  insoluble 
in  pure  water  and  in  neutral  saline  solutions,  but  soluble  in  slightly 
alkaline  liquids.  In  liquids  containing  an  alkaline  phosphate,  like  milk, 
it  remains  in  solution  notwithstanding  the  alkaline  reaction  be  neutral- 
ized (Hoppe-Seyler).  It  is  not  affected  by  a  boiling  temperature,  but 
coagulates  by  most  of  the  other  agents  which  have  this  effect  on 
albumen,  namely,  by  the  mineral  acids,  the  metallic  salts,  and  alcohol. 
It  is  furthermore  thrown  down  by  the  organic  acids  and  by  magnesium 
sulphate,  both  of  which  are  without  action  on  albumen.  Its  specific 
rotary  power  for  polarized  light  is  greater  than  that  of  any  other 
albuminous  matter,  amounting  to  80°.  Its  most  remarkable  property 
is  that  of  coagulating  by  contact  with  rennet,  or  the  extract  of  the  calf's 
stomach.  Coagulated  caseine  forms  the  albuminous  ingredient  of 
cheese,  whence  its  name  is  derived.  When  milk  is  taken  as  food  it  is 
coagulated  in  a  similar  way,  in  the  stomach,  by  the  ferment  of  the 
gastric  juice.  Caseine,  in  its  various  forms  of  preparation,  is  an  abun- 
dant and  important  nutritious  material. 

4.  Paraglobuline. 

This  substance  is  a  constituent  of  the  blood-plasma,  where  it  exists 
in  the  proportion  of  22  parts  per  thousand,  being  a  little  less  than  one- 
half  as  abundant  as  the  albumen.  After  coagulation  of  the  blood 
it  remains,  together  with  the  albumen,  as  an  ingredient  of  the  serum. 
Its  name  is  derived  from  the  fact  that  it  has  similar,  but  not  identical, 
reactions  with  a  substance  formerly  extracted  from  the  blood-globules, 

d  by  Lehmann  termed  "globuline ; "  one  of  the  most  prominent  of 

ese  reactions  being  its  precipitation  from  dilute  blood-serum  or  saline 
solutions  by  a  stream  of  carbonic  acid,  or  by  the  addition  of  very  dilute 
tic  acid.  Paraglobuline  belongs  to  a  group  of  substances,  including 
he  two  following,  which  are  insoluble  in  pure  water,  but  soluble  in 
dilute  solutions  of  sodium  chloride,  in  which  they  are  coagulable  by 
heat.  If  the  serum  of  the  blood,  accordingly,  be  subjected  to  a  boiling 
temperature,  the  whole  of  its  albumen  and  paraglobuline  coagulate 
together ;  but  if  it  be  diluted  with  ten  times  its  volume  of  water,  and 
then  treated  with  a  stream  of  carbonic  acid,  its  paraglobuline  will  be 
thrown  down,  while  the  albumen  remains  behind.  Paraglobuline  is 
also  precipitable  from  blood-serum  by  the  addition  of  powdered  sodium 
chloride  in  excess. 

The  physiological  relations  of  paraglobuline  with  albumen  are 
unknown.  The  similarity  in  properties  and  quantity  of  the  two  sub- 
stances, as  ingredients  of  the  blood,  make  it  possible  that  either  one 
may  be  a  product  of  metamorphosis  from  the  other ;  or  they  may  both 
have  been  formed  out  of  some  other  preceding  substance,  to  serve  for 
different  purposes  in  the  act  of  nutrition. 

F 


ret 

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sol. 

I 


PHYSIOLOGICAL,     CHEMISTRY. 

5.  Fibrinogen. 

This  substance  exists  in  a  fluid  form  in  the  biood  of  the  living  body, 
and  at  the  time  of  its  coagulation  is  converted  into  fibrine.  It  is  pres- 
ent in  the  blood  in  much  smaller  quantity  than  its  other  albuminous 
ingredients,  amounting  to  not  more  than  3  parts  per  thousand.  Like 
paraglobuline,  it  is  insoluble  in  water,  but  soluble  in  neutral  saline 
solutions,  and  in  this  condition  is  coagulable  by  heat.  It  is  also 
thrown  down  from  fluids  which  contain  it  by  a  stream  of  carbonic  acid, 
or  by  dilute  acetic  acid.  Its  most  striking  character  is  its  liability  to 
coagulate  by  contact  with  a  special  ferment,  the  so-called  "  fibrine- 
ferment,"  which  is  considered  as  the  natural  exciting  cause  of  its  coag- 
ulation. This  process  is  analogous  to  the  coagulation  of  caseine  by 
rennet ;  the  fibrine-ferment  acting  only  by  contact,  while  the  fibrinogen 
supplies  the  material  of  the  solidified  fibrine.  If  pure  fibrinogen,  in  a 
dilute  saline  solution,  be  coagulated  by  heat,  the  quantity  of  coagulum 
so  obtained  is  as  great  as  that  produced  from  coagulation  by  action  of 
the  ferment  (Fredericq).  This  shows  that  the  spontaneous  coagulation 
of  fibrinogen  in  the  blood  does  not  depend  upon  its  union  with  another 
substance,  but  that  it  is  simply  a  change  of  molecular  condition,  like  that 
which  occurs  in  other  coagulable  substances. 

Fibrinogen  is  best  obtained  from  horse's  blood,  according  to  the 
method  of  Hammarsten.*  The  blood,  as  it  escapes  from  the  vessels,  is 
received  into  ^  of  its  volume  of  a  saturated  solution  of  magnesium 
sulphate,  with  which  it  is  thoroughly  mingled.  This  arrests  its  coag- 
ulation. The  mixture  is  then  slowly  filtered,  to  separate  the  blood- 
globules,  and  the  clear  filtered  fluid  is  treated  with  its  own  volume  of 
a  saturated  sodium  chloride  solution.  This  throws  down  the  fibrinogen 
with  some  other  albuminous  matters.  To  effect  its  purification,  the 
precipitate  is  cleansed  from  the  adherent  liquid  by  pressure  with  bibu- 
lous paper,  finely  divided,  dissolved  in  a  sodium  chloride  solution  of  the 
strength  of  8  per  cent.,  and  again  precipitated  by  the  same  salt  in 
saturated  solution.  This  operation  is  once  more  repeated;  and  after 
the  third  precipitation  with  saturated  sodium  chloride  solution,  the 
fibrinogen  is  redissolved  in  pure  water.  It  is  then  in  a  state  of  purity. 

Fibrine,  produced  by  the  coagulation  of  fibrinogen,  is  a  tenacious 
whitish  substance,  of  firmer  consistency  than  coagulated  albumen.  It 
has  a  considerable  degree  of  extensibility  and  elasticity,  and  will 
retract  with  sufficient  force  to  gradually  expel  any  surplus  liquid 
entangled  in  it.  It  is  insoluble  in  water  and  in  neutral  saline  solu- 
tions. It  is  swollen  and  softened,  but  not  liquefied,  at  ordinary  temper- 
atures, by  dilute  acids,  and  is  slowly  dissolved  by  dilute  alkalies.  If 
heated  in  contact  with  moisture,  or  treated  with  alcohol,  it  is  rendered 
opaque,  loses  its  extensibility  and  elasticity,  and  becomes  in  appearance 
more  like  coagulated  albumen.  It  forms  the  solidified  portion  of  inflam- 
matory exudations  on  serous  surfaces  or  in  the  tissue  of  diseased  organs. 


*  Arehiv  fiir  die  i:«^:iiniiitr  Physiologic.      P.onn,  1ST'.).  15:md  XIX..  \>. 


ALBUMENOID    SUBSTANCES.  83 

6.  Myosine. 

The  contractile  substance  of  the  striped  muscular  fibres  during  life 
consists  largely  of  a  thickish  fluid  or  semifluid  alkaline  plasma.  After 
death  it  coagulates,  and  the  coagulating  substance,  termed  "myosine," 
presents  some  analogy  with  the  fibrinous  matter  of  the  blood.  Its 
spontaneous  coagulation  gives  rise  to  the  condition  of  cadaveric  rigid- 
ity, in  which  the  muscular  fibres  lose  their  power  of  contraction  and 
relaxation,  becoming  solidified  and  opaque.  At  the  same  time  the 
reaction  of  the  muscular  tissue  changes  from  alkaline  to  acid. 

The  coagulation  of  the  muscular  plasma,  like  that  of  the  blood,  is 
retarded  for  a  time  by  the  action  of  cold ;  and  it  takes  place  less 
rapidly,  after  death,  in  the  cold-blooded  than  in  the  warm-blooded 
animals.  This  fact  has  been  used  by  Ku'hne  for  its  extraction,  from 
the  muscular  tissue  of  frogs,  in  a  liquid  condition.  The  vascular 
system  is  first  deprived  of  blood  by  an  injection  of  a  one-half  per  cent, 
solution  of  sodium  chloride.  The  muscles,  thoroughly  washed,  are  then 
subjected  for  two  hours  to  a  temperature  of  1°  to  10°  C.  below  the 
freezing-point,  reduced  to  a  pulp  in  a  cold  mortar,  and  then  allowed 
gradually  to  thaw  upon  a  filter.  As  the  temperature  rises  the  filtered 
fluid  coagulates. 

Coagulated  myosine  is  a  gelatinous  amorphous  substance,  insoluble 
in  water  and  in  concentrated  solutions  of  sodium  chloride ;  but  is  dis- 
Ived  by  a  watery  solution  of  salt,  made  in  the  proportion  of  ten  per 
mt.  or  less.     It  may  be  extracted  after  death  by  bruising  the  muscu- 
r  tissue  to  a  pulp  in  a  ten  per  cent,  solution  of  sodium  chloride,  filter- 
g  the  expressed  liquid,  and  allowing  it  to  fall  by  drops  into  a  large 
uantity  of  distilled  water,  when  the  myosine  separates  by  precipita- 
on.     It  is  distinguished  from  coagulated  fibrine  by  its  solubility  in 
neutral  saline  solutions  of  a  certain  strength,  as  well  as  by  its  ready 
solubility  in  feebly  acidulated  solutions.     When  dissolved  in  a  neutral 
line  fluid  it  is  coagulable  by  heat,  like  the  albumen  of  blood. 

7.  Syntonine. 

Syntonine  is  so  called  because  formerly  supposed  to  be  the  contractile 
ingredient  of  muscular  flesh,  from  which  it  was  obtained  by  extraction 
with  a  dilute  acid.     But  a  substance  having  the  same  characters  may 
be  extracted  by  similar  means  from  many  of  the  animal  solids  and 
"uids.     Any  one  of  the  albuminous  matters,  if  treated  with  a  solution 
*  hydrochloric  acid  of  about  4  parts  per  thousand,  after  a  time  dis- 
>lves  and  becomes  altered  in  its  properties,  so  that  it  is  soluble  in 
sither  dilute  acids  or  alkalies,  but  insoluble  in  neutral  watery  liquids 
id  saline  solutions.     Its  solution  in  a  dilute  alkali  is  coagulable  by 
sat,  and  if  previously  boiled  in  water  it  becomes  insoluble  in  dilute 
:ids.     It  appears  to  be  identical  in  character,  from  whatever  source  it 
derived. 

Obtained  by  the  above  means,  syntonine  is  an  artificial  product, 
•ut  the  same  substance  is  formed  in  the  stomach  during  digestion  by 


S4  I'll  YStOLOGICAL    CHEMISTRY. 

the  action  of  the  acid  gastric  juice  upon  the  albuminous  elements  of  the 
food.  It  is  the  first  stage  in  the  digestive  process,  by  which  all  these 
substances  are  reduced  to  the  form  of  syntonine.  It  may  be  precipi- 
tated from  its  solution  in  the  gastric  juice  by  careful  neutralization 
with  an  alkali.  This  is  the  only  situation  in  the  body  in  which 
syntonine  is  known  to  be  normally  present. 

8.  Peptone. 

This  substance  is  the  final  product  of  the  stomach  digestion  of  albu- 
minous matters.  These  matters,  first  converted  into  syntonine  by  the 
acid  of  the  gastric  juice,  are  further  transformed  by  the  action  of  its 
ferment  or  "pepsine."  The  result  of  this  transformation  is  peptone; 
and  it  appears  to  be  essentially  the  same  substance,  whether  derived 
from  the  digestion  of  coagulated  albumen,  fibrine,  myoaine,  or  other 
nutritious  albumenoids.  It  is  soluble  in  water,  in  dilute  acid  and 
alkaline  liquids,  and  in  neutral  saline  solutions  in  all  proportions.  Even 
strong  mineral  acids  have  no  effect  upon  it.  It  is  not  coagulated  by 
heat,  nor  by  potassium  ferrocyanide  in  acidulated  solution,  a  reagent 
so  prompt  and  effective  for  albuminous  matters  in  general ;  though  it 
is  thrown  down  by  alcohol  in  excess  and  by  the  metallic  salts.  It  has 
therefore  acquired,  in  comparison  with  other  substances  of  this  group, 
an  increased  range  of  solubility. 

But  its  most  distinctive  feature  is  its  diffusibility.  Unlike  other 
albuminous  matters,  it  passes  readily  through  animal  membranes  or 
parchment  paper.  Comparative  experiments  on  the  two  substances 
show  that  the  diffusibility  of  peptone  is  about  twelve  times  as  great  as 
that  of  albumen.  By  this  means  it  is  enabled  to  leave  the  cavity  of 
the  alimentary  canal,  and  to  pass  through  the  walls  of  the  blood-vessels 
into  the  circulation. 

The  transformation  of  albuminous  matters  into  peptone  is  a  phenom- 
enon of  catalysis.  It  does  not  represent  any  fundamental  change  in 
the  chemical  composition  of  these  bodies,  since  the  elementary  analyses 
of  peptone,  thus  far  made,  show  that  it  contains  nearly  the  same  pro- 
portions of  carbon,  hydrogen,  nitrogen,  oxygen,  and  sulphur  as  the 
substances  from  which  it  is  produced.  The  principal  modification 
which  takes  place  seems  to  consist  in  the  assumption,  by  the  original 
albuminous  matter,  of  the  elements  of  water, — that  is,  in  a  hydration. 
This  is  claimed  as  proved  by  direct  experiment;  and  it  is  held  by 
observers  of  high  repute,*  that  peptone  is  simply  an  albuminous 
substance  in  its  state  of  maximum  hydration,  retaining  its  chemical 
qualities  and  nutritive  value,  but  altered  in  its  physical  properties  of 
solubility  and  diffusibility.  If  this  view  be  correct,  peptone  will 
stand  in  its  relation  to  albumen  very  much  as  glucose  in  its  relation  to 
glycogen  and  starch. 

The  fresh  juices  of  growing  plants,  and  especially  of  the  succulent 
vegetables,  contain  a  nitrogenous  substance  coagulable  by  heat,  and 

iI,.ppi-Seylur,  I'hysiologische  Chemie.   Berlin, 


ALBUMENOID    SUBSTANCES.  85 

corresponding  with  albuminous  matters  in  chemical  composition.  It 
is  known  as  "  vegetable  albumen."  In  peas  and  beans  there  is  also 
a  substance,  termed  "  legumine,"  similar  to  the  caseine  of  milk.  It  Is 
not  coagulated  by  heat,  but  is  thrown  down  both  by  the  organic  acids 
and  by  magnesium  sulphate  in  excess.  According  to  some  observers  it 
is  also  coagulable  by  rennet.  The  cereal  grains,  and  especially  wheat, 
contain  a  substance  insoluble  in  water,  which,  in  its  tenacity,  extensi- 
bility, and  elasticity,  resembles  coagulated  fibrine.  It  is  this  substance 
which  gives  consistency  to  the  dough  made  from  wheaten  flour,  enabling 
it  to  retain  the  starchy  materials  in  a  consistent  mass. 

FERMENTS. 

The  substances  belonging  to  this  group  are  distinguished  from  the 
preceding ;  First,  by  their  inferior  quantity.  Their  amount  is  usually 
too  small  to  allow  either  of  exact  chemical  analysis  or  quantitative 
determination  ;  and  they  are  known  more  from  their  effects  than  from 
their  physical  characters.  Secondly,  their  action  is  one  of  catalysis. 
They  do  not  directly  form  the  materials  of  nutrition,  but  they  cause  in 
these  materials  the  changes  requisite  for  assimilation.  For  this  reason 
they  are  not  perceptibly  consumed  in  the  process ;  a  very  small  quan- 
,  tity  of  the  ferment  being  sufficient  to  produce  the  needed  result  in  a 
large  quantity  of  material.  Thirdly,  when  heated,  in  watery  solution, 
to  the  boiling  point,  their  properties  are  changed  and  they  become 
inactive  as  ferments.  This  fact,  which  is  denied  by  some  writers,  has 
been  unmistakably  evident  in  our  own  observations,  and  appears  to  be 
amply  confirmed  by  the  experience  of  others.*  Fourthly,  the  ferments 
are  precipitated  from  their  solutions  by  alcohol  in  excess.  But  there  is 
a  marked  difference,  in  this  respect,  between  them  and  the  albuminous 
matters  proper.  An  albuminous  matter,  coagulated  by  alcohol,  is  per- 
manently altered,  and  cannot  be  again  rendered  soluble  except  by 
means  which  still  further  modify  its  character.  A  ferment,  on  the 
other  hand,  when  thrown  down  by  alcohol,  may  be  kept  in  this  con- 
dition for  an  indefinite  time ;  and,  after  the  removal  of  the  alcohol,  if 
redissolved  in  water,  will  again  exhibit  its  characteristic  activity.  The 
ferments  may  also  be  extracted  and  preserved  by  the  action  of  glycerine, 
which  is  often  used  as  a  convenient  means  for  their  preparation. 

1.  Ptyaline. 

This  is  a  ferment  belonging  to  human  saliva,  which  has  the  prop- 
erty of  converting  boiled  starch  into  sugar.  Its  action  takes  place 
most  readily  in  a  slightly  alkaline  solution,  at  the  temperature  of  the 
living  body.  It  is  obtained  in  comparative  purity  by  adding  to 
the  saliva  dilute  phosphoric  acid,  and  neutralizing  the  solution  with 
lime-water.  The  precipitate  of  lime  phosphate  thus  produced  brings 

*  Hoppe-Seyler,  Physiologische  Chemie.  Berlin,  1878,  p.  113.  Gorup-Besanez, 
Lehrbuch  der  Physiologischen  Chemie.  Braunschweig,  1878,  p.  504.  Ewald,  Die 
Lehre  von  der  Verdanung.  Berlin,  1879,  p.  122. 


86  PHYSIOLOGICAL    CHEMISTRY. 

down  with  it  the  ptyaline,  which  may  afterward  be  dissolved  in  water, 
precipitated  by  alcohol  from  its  watery  solution,  and  again  dissolved  in 
water.  Evaporated  to  dryness,  it  is  an  amorphous  nitrogenous  sub- 
stance, and  when  heated  to  decomposition,  gives  off  the  odor  of  burnt 
horn.  It  appears  to  be  constantly  present  in  human  saliva,  within  a 
short  time  after  birth,  and  in  that  of  the  gnawing  animals,  as  rabbits 
and  guinea-pigs ;  but  is  not  found  in  that  of  the  dog  or  horse. 

2.  Pepsine. 

Pepsine  is  the  digestive  ferment  of  the  gastric  juice,  by  which  the 
albuminous  matters  of  the  food  are  transformed  into  peptone.  It 
operates  only  in  an  acidulated  solution,  since  the  influence  of  an  acid  is 
necessary  for  the  preliminary  conversion  of  albuminous  matter  into 
syntonine.  It  requires  also  a  moderately  elevated  temperature,  that 
of  the  living  body  being  most  favorable.  Pepsine  is  prepared  from 
gastric  juice,  according  to  the  method  of  Schmidt,  by  neutralizing  the 
fresh  juice  with  lime-water,  evaporating  the  filtered  liquid  to  a  syrupy 
consistency,  and  precipitating  with  absolute  alcohol.  The  precipitate 
is  redissolved  in  water,  again  thrown  down  by  chloride  of  mercury, 
and  the  metallic  precipitate  decomposed  by  sulphuretted  hydrogen. 
The  filtered  fluid  contains  pepsine  in  solution. 

It  is  also  obtained  from  the  mucous  membrane  of  the  pig's  stomach, 
which  is  cut  into  small  pieces  and  digested  for  several  days  with 
glycerine.  The  glycerine  extract  is  then  treated  by  a  large  addition  of 
alcohol,  and  the  pepsine,  thus  precipitated,  after  being  washed  with 
alcohol,  is  dissolved  in  water.  The  solutions  obtained  by  these  proc< 
are  not  supposed  to  contain  the  ferment  in  a  perfectly  pure  state ;  but 
if  slightly  acidulated,  they  will  exhibit  its  digestive  action  on  albumin- 
ous matters  at  the  temperature  of  the  body  with  considerable  eneriry. 
Pepsine  is  a  non-diffusible  substance,  soluble  in  water  and  in  glycerine. 
It  is  not  precipitated  by  the  mineral  acids.  It  exists,  with  essentially 
the  same  properties,  in  the  gastric  juice  and  gastric  mucous  membrane 
of  all  animals  hitherto  examined,  and  is  found  in  the  stomach  of  the 
human  embryo  as  early  as  the  beginning  of  the  fourth  month. 

3.  Pancreatic  Ferments. 

In  the  secretion  of  the  pancreas  there  are,  beside  a  certain  quantity 
of  albuminous  matter,  no  less  than  three  ferments,  differing  in  their 
mode  of  action.  The  most  important  of  these  is  "pancreatine,"  or 
the  sugar-producing  ferment.  It  acts  in  a  similar  manner  to  ptyaline, 
but  with  greater  energy;  being,  according  to  all  observers,  by  far  the 
most  prompt  and  effective  of  all  known  substances  for  the  conversion 
of  starch  into  sugar.  It  is  obtained  by  digesting  the  chopped  pn  norms 
in  linn '-water,  after  which  the  solution  is  neutralized  by  phosphoric 
acid,  producing  a  precipitate  of  lime  phosphate,  by  which  the  ferment 
is  thrown  down,  entangled  with  other  organic  matters.  As  these  im- 
purities are  more  firmly  fixed  by  the  calcareous  salt  than  the  ferment, 


14V4.V 

= 


2 


ALBUMENOID    SUBSTANCES.  87 

the  latter  can  be  extracted  by  water,  and  subsequently  precipitated  by 
alcohol  from  its  watery  solution.  It  is  wanting  in  the  pancreas  of 
newly-born  infants. 

The  second  pancreatic  ferment  is  known  as  "trypsine,"  from  its 
softening  effect  on  coagulated  albuminous  matters.  It  acts  upon  them 
somewhat  like  the  gastric  ferment,  transforming  them  into  peptone. 
The  pancreatic  juice,  as  well  as  the  extract  of  the  pancreatic  tissue,  cer- 
tainly contains  a  substance  capable  of  digesting  and  dissolving  coagu- 
lated albumen  or  fibrine  ;  but  this  action  is  effected  with  readiness  only 
in  an  alkaline  or  neutral  fluid,  and  is  soon  followed  by  putrescence.  In 
an  acidulated  solution  it  goes  on  with  difficulty  or  not  at  all,  and  accord- 
ing to  Hoppe-Seyler  is  distinctly  interfered  with  by  the  presence  of 
hydrochloric  acid  in  the  proportion  of  one  part  per  thousand.  It  is 
doubtful  how  far  it  takes  place  during  digestion  in  the  fluids  of  the  small 
intestine,  which  have  normally  an  acid  reaction.  Pancreatine  and  tryp- 
sine  are  accordingly  two  distinct  substances  with  different  properties, 
the  former  having  an  action  upon  starch,  the  latter  upon  albuminous 
matters.  They  are  also,  according  to  Langendorff,*  produced  in  the 
embryo  at  different  periods  of  development ;  trypsine  showing  itself  at 
the  beginning  of  the  fifth  month,  while  pancreatine  only  appears  after 
birth. 

The  third  ferment  in  the  pancreatic  juice  is  one  which  causes  the 
acidification  of  neutral  fats.     This  change  may  be  produced  with  either 
creatic  juice,  infusions  of  the  gland,  or  fresh  moist  pieces  of  the 
land  tissue,  placed  in  contact,  at  38°  C.,  with  liquid  neutral  fat ;  their 
ormal  alkalescence  giving  place,  after  a  time,  to  an  acidity  due  to  the 
ration  of  fatty  acid.     So  long  as  any  surplus  alkali  remains,  the 
mposed  fat  is  saponified ;  but  the  proportion  which  undergoes  this 
additional  modification  seems  to  be  normally  a  small  one.     The  pan- 
natic  ferment  which  causes  acidification  of  the  fats  has  not  been  ob- 
ined  in  a  separate  form. 

4.  Fibrine-ferment. 

This  is  the  substance  which  induces  the  coagulation  of  fibrinogen 
and  the  production  of  fibrine  in  freshly  drawn  blood.  It  acts  in  such 
minute  quantity  that  its  physical  and  chemical  characters  have  not 
been  accurately  determined,  and  even  its  source  is  not  fully  known.  But 
in  some  way  or  other  it  appears  in  the  blood  soon  after  its  discharge 
from  a  wounded  vessel,  or  even  when  its  circulation  has  been  arrested 
a  ligature.  It  seems  to  be  exuded,  perhaps  from  the  interstitial 

ids,  wherever  the  walls  of  the  blood-vessels  are  divided,  bruised, 
degenerated,  or  inflamed ;  for  at  these  situations  the  blood  always 
coagulates.  It  is  obtained,  according  to  the  method  of  Schmidt,  f  from 
blood-serum  by  coagulating  it  with  15  or  20  times  its  volume  of  strong 
alcohol,  and  allowing  the  mixture  to  remain  for  two  weeks,  to  secure 


*  Archiv  fur  Anatomie  und  Physiologic.     Leipzig,  1879,  p.  95. 

f  Archiv  fiir  die  gesammte  Physiologic.     Bonn,  1872,  Band  VI.,  p.  413. 


88  PHYSIOLOGICAL    CHEMISTRY. 

complete  insolubility  of  the  albumin6us  matters.  The  coagulum  is  then 
dried,  pulverized,  treated  with  water  to  double  the  original  volume  of 
the  serum,  and  the  watery  extract  filtered.  The  filtered  solution  con- 
tains the  ferment,  and  if  added  to  a  fluid  containing  fibrinogen  will 
cause  its  coagulation. 

5.  Diastase. 

Diastase  is  a  vegetable  nitrogenous  matter,  produced  in  the  germina- 
tion of  the  cereal  grains,  and  especially  of  barley,  by  which  their 
starch  is  converted  into  dextrine  and  sugar.  It  may  be  extracted  from 
malting  barley  with  water,  the  concentrated  watery  extract  being 
precipitated  by  alcohol,  and  the  precipitate  dried  and  redissolved  in 
water.  Its  action  is  most  rapid  in  a  neutral  menstruum  and  at  mod- 
erately warm  temperatures,  ceasing  about  75°  C.  It  is  considered  as 
the  representative  of  the  sugar-producing  bodies  of  this  group,  all 
those  having  a  similar  action  being  designated  as  "diastatic"  ferments. 

MUCIFORM,   GELATINOUS,   AND   SOLID  ALBUMENOID   SUB- 
STANCES. 

The  substances  of  this  group  are  distinguished  rather  by  their  con- 
sistency than  by  their  active  chemical  or  physiological  properties.  They 
do  not  form  part  of  the  nutritious  juices,  like  albuminous  matters,  nor 
give  rise  to  chemical  transformations  like  the  ferments.  They  have 
reached  their  final  stage  in  the  constructive  nutrition  of  the  body,  and 
are  useful  in  facilitating  the  mechanical  movement  of  the  parts,  or  in 
holding  the  other  ingredients  of  the  tissues  in  a  coherent  mass.  They 
are  not  easily  affected  by  chemical  influences,  and  most  of  them  show 
great  resistance  to  the  action  of  ordinary  alkaline  or  acidulated  liquids. 
As  a  rule,  they  constitute  the  organic  part  of  the  solid  tissues. 

1.  Mucine. 

There  are  various  secretions  in  the  body  designated  by  the  common 
name  of  "  mucus,"  and  distinguished  by  a  peculiar  physical  character 
of  viscidity  and  lubricity.  This  consistency  is  due  to  the  presence  of 
mucine.  It  exists  in  all  the  varieties  of  mucus,  some  of  which,  like 
those  of  the  bronchial  tubes  and  intestines,  are  nearly  fluid,  while 
others,  like  that  of  the  cervix  uteri  during  pregnancy,  are  gelatinous 
and  semi-solid.  It  is  also  present  in  the  synovia,  the  secretion  of  the 
u'all-bladder,  and  the  saliva  of  the  submaxillary  and  sublingual  glands. 
The  secretion  of  the  mucous  follicles  of  the  mouth  consists  of  it  almost 
exclusively.  Like  the  albuminous  matters,  it  contains  carbon,  hydro- 
gen, nitrogen,  and  oxygen,  but  is  destitute  of  sulphur.  In  pure  water 
il  swells  up  without  becoming  liquid,  but  it  is  soluble  in  alkalescent 
solutions,  particularly  in  those  of  the  alkaline  earths,  as  lime-water  and 
baryta-water.  It  is  not  affected  by  boiling,  but  is  precipitated  by  acetic 
arid.  It  is  thought  to  be  held  in  solution  in  the  mucous  secretions  l>y 
their  free  alkali  ;  the  varying  consistency  of  the  secretions  bring  due 


til] 

• 


ALBUMENOID    SUBSTANCES.  89 

to  the  quantity  of  alkali  which  they  contain.  Mucine  is  unaffected  by 
most  of  the  metallic  salts,  lead-subacetate  being  the  only  one  which 
produces  a  distinct  coagulation.  In  some  cases,  as  in  the  bile,  it  is  dis- 
solved in  the  fluid  ingredients  of  the  secretions,  from  which  it  may  be 
separated  by  alcohol.  In  others,  as  in  the  urine,  it  is  only  mechanically 
suspended,  subsiding  as  a  light  deposit  after  a  few  hours'  repose. 

Mucine  is  useful  mainly  by  lubricating  the  opposite  surfaces  of 
adjacent  organs,  as  in  the  synovial  cavities ;  by  protecting  mucous  mem- 
branes from  the  air,  as  in  the  trachea  and  bronchi  or  by  facilitating  the 
mastication  and  deglutition  of  food,  as  in  the  secretions  of  the  mouth 
and  subniaxillary  glands. 

2.  Gelatine. 

This  substance  is  very  widely  diffused  in  the  animal  body,  forming 
the  more  or  less  homogeneous  interstitial  mass  of  the  bones,  perios- 
teum, tendons,  ligaments,  fasciae,  and  connective  tissues  generally.  All 
these  tissues,  although  at  firs't  insoluble  in  boiling  water,  become  dis- 
solved after  long  ebullition ;  and  the  dissolved  matter  solidifies,  on  cool- 
ing, into  a  jelly-like  mass.  This  substance  is  the  animal  principle  of 
glue.  It  was  formerly  doubted  whether  gelatine  represents  the  original 
ingredient  of  the  fibrous  and  bony  tissues,  or  an  altered  product  due  to 
continued  ebullition.  Comparative  analyses,  however,  of  the  gelatige- 
nous  tissues  and  of  the  gelatine  extracted  from  them  have  shown  that 
there  is  not  only  no  appreciable  difference  in  their  chemical  constitu- 
tion, but  that  the  solid  residue  of  the  dried  tissue  and  that  of  the  gela- 
tine extracted  from  it  are  the  same  in  weight.  (Hoppe-Seyler.) 

A  hot  solution  of  this  substance  gelatinizes  on  cooling  when  present 

the  proportion  of  3  per  cent. ;  below  this  quantity,  or  if  the  boiling 
repeated,  it  may  remain  liquid.  Its  solution  rotates  the  plane  of 
polarization  to  the  left  130°.  It  is  thrown  down  by  alcohol  and  by 
tannic  acid.  The  last,  which  is  the  only  acid  by  which  this  substance 

precipitated,  is  a  very  sensitive  test  of  its  presence ;  and,  according 
to  Hardy,*  will  detect  one  part  of  gelatine  in  5,000  parts  of  water.  A 
similar  combination  takes  place,  in  the  process  of  tanning,  between 
tannic  acid  and  the  substance  of  the  fibrous  tissues,  by  which  they  are 
rendered  harder,  more  impermeable  to  water,  and  incapable  of  putre- 
faction. Gelatine  is  not  affected  by  potassium  ferrocyanide  with  acetic 
acid,  nor  by  lead  subacetate.  It  contains  sulphur  as  one  of  its  ingredients. 


3.  Chondrine. 

The  intercellular  substance  of  cartilage  resembles  that  of  the  bones 
and  the  fibrous  tissues  in  yielding,  by  prolonged  boiling  with  water,  a 
substance  which  will  gelatinize  on  cooling.  In  the  case  of  the  carti- 
lages, however,  this  substance  is  termed  chondrine,  from  the  source 
from  which  it  is  derived.  Chondrine,  like  gelatine,  contains  sulphur, 

*Chimie  Biologique.     Paris,  1871,  p.  282. 


90  PHYSIOLOGICAL    CHEMISTRY. 

and  presents  for  the  most  part  similar  chemical  reactions.  It  differs 
from  gelatine  in  being  precipitated  from  its  watery  solution  by  both 
acetic  acid  and  lead  subacetate.  It  rotates  the  plane  of  polarization  to 
the  left  213.5°. 

4.  Elastine. 

The  fibres  of  all  the  yellow  elastic  tissues,  as  in  the  middle  coat  of 
the  larger  arteries,  the  elastic  ligaments  of  the  spinal  column,  and  the 
ligamcntum  nuchae,  consist  mainly  of  a  homogeneous  substance  dis- 
tinguished by  its  refractory  nature  toward  chemical  reagents.  It  is 
obtained  by  boiling  the  elastic  tissues  successively  with  alcohol,  ether, 
water,  acetic  acid,  dilute  soda  solution,  and  dilute  hydrochloric  acid. 
The  elastine,  thus  purified  from  other  ingredients,  is  not  itself  soluble 
in  either  of  the  above  liquids.  It  is  not  converted  into  gelatine  even 
by  long  boiling ;  and  it  is  dissolved,  but  at  the  same  time  decomposed, 
only  by  the  concentrated  acids  and  alkalies.  The  slender  elastic  fibres 
mingled  with  connective  tissue,  and  the  sarcolemma  of  the  striped 
muscular  fibres,  are  probably  composed  of  the  same  substance.  Elas- 
tine contains  no  sulphur. 

5.  Keratine. 

This  is  the  exceedingly  resisting  and  indestructible  substance  of  the 
hair,  nails,  epidermis,  feathers,  and  all  horny  tissues.  It  is  unaffected 
by  boiling  with  alcohol,  ether,  water,  or  the  dilute  acids.  By  continu- 
ous boiling  in  a  Papin's  digester  at  150°  C.  it  is  liquefied  and  partly 
decomposed.  It  is  distinguished  from  the  preceding  substance  by  con- 
taining sulphur  as  an  ingredient ;  and  when  decomposed  by  boiling 
under  pressure  or  with  concentrated  alkalies,  it  gives  rise  to  hydrogen 
sulphide  vapors. 

Source,  Changes,  and  Destination  of  the  Albumenoid  Substances. — 
The  source  of  albumenoid  substances  in  the  animal  body  is  in  the 
food.  Herbivorous  animals  take  them  ready  formed  in  the  juices  and 
parenchyma  of  plants,  and  the  carnivora  are  supplied  with  them  in 
still  greater  quantity  in  the  animal  tissues.  Man  obtains  them  from 
both  sources,  and  all  nutritious  articles  of  food  contain  them  in  greater 
or  less  abundance.  According  to  the  estimates  of  Pay  en,  which  cor- 
respond very  closely  with  our  own  observations,  an  adult  man  requires 
a  daily  supply  of  about  130  grammes  of  albumenoid  matter  to  provide 
for  the  wants  of  the  system  ;  and  this  quantity  is  actually  contained  in 
the  food  consumed. 

But  although  albumenoid  matter  is  thus  abundantly  supplied  to  the 
system  from  without,  yet  the  particular  substances  characteristic  of  the 
various  tissues  and  fluids  are  formed  within  the  body,  by  transformation 
of  those  introduced  with  the  food.  None  of  the  albumenoids  contained 
in  the  food  of  an  herbivorous  animal  are  precisely  identical  with  those 
of  his  own  body.  All  the  tissues  and  juices  of  the  embryo  chick  arc 
formed  from  the  albumen  of  the  egg ;  and  the  nourishment  of  all  the 
organs  of  tin-  infant  is  provided  at  the  expense  of  caseine,  the  albumen- 


ALBUMENOID    SUBSTANCES. 


91 


old  element  of  milk.  There  are  many  different  kinds  of  these  sub- 
stances in  the  solid  parts  and  secretions  of  the  adult  body,  but  not  one 
of  them  is  contained  under  its  own  form  in  the  blood,  from  which  all 
the  nutritious  material  for  the  tissues  and  glands  is  supplied.  It  is 
evident  that  the  albumenoid  substances  finally  present  in  the  animal 
frame  are  produced  by  transformation  from  those  contained  in  the  food 
and  in  the  blood. 

Only  a  very  small  proportion  of  the  albumenoid  substances  is  dis- 
charged with  the  excretions.  Those  contained  in  the  perspiration,  the 
sebaceous  matter,  and  the  mucus  of  the  urinary  bladder  and  large 
intestine  are  almost  the  only  ones  which  find  an  exit  in  this  way.  A 
very  little  albumenoid  matter  is  exhaled  in  a  volatile  form  with  the 
breath,  and  a  little  also,  in  all  probability,  from  the  skin.  But  the  entire 
quantity  so  discharged  bears  an  insignificant  proportion  to  that  intro- 
duced with  the  food.  The  albumenoid  substances,  accordingly,  are 
decomposed  in  the  interior  of  the  body.  After  being  produced  by 
metamorphosis  in  the  act  of  nutrition,  they  are  still  further  trans- 
formed in  the  process  of  destructive  assimilation,  and  they  are  repre- 
sented, in  the  excreted  products,  by  other  combinations  of  a  different 
form. 


CHAPTER  V. 
COLORING   MATTERS. 

SOME  of  the  animal  tissues  and  fluids  are  distinguished,  in  addition 
to  their  other  features,  by  characteristic  colors,  due  to  the  presence 
of  certain  coloring  matters.  In  some  instances,  as  in  the  red  globules 
of  the  blood,  and  the  green  leaves  of  plants,  the  coloring  matters  are 
directly  connected  with  active  physiological  functions.  In  others,  as 
in  the  choroid  coat  of  the  eye,  they  are  essential  to  the  physical  phe- 
nomena of  the  organs  to  which  they  belong.  But  notwithstanding  the 
evident  importance  of  these  substances,  and  the  striking  character  of 
their  optical  properties,  they  are  in  many  respects  more  difficult  of  study 
than  the  other  ingredients  of  the  body.  This  is  partly  due  to  the  com- 
paratively small  quantity  in  which  they  occur,  and  to  the  readiness  with 
which  they  are  decomposed  or  altered  in  the  process  of  separation  ;  and 
it  is  sometimes  difficult  to  decide  whether  a  variation  of  tint  be  due  to 
the  different  proportions  of  several  coloring  matters  or  to  the  varying 
degrees  of  concentration  of  a  single  one. 

The  coloring  matters  are  all  nitrogenous  compounds,  but  differ  in 
essential  particulars  from  the  albumenoid  substances.  Those  which 
have  been  most  fully  examined  are  known  to  be  crystallizable ;  and 
it  is  probable  that  all  of  them  might  be  obtained  in  a  crystalline  form, 
could  they  be  completely  separated  without  decomposition.  The  most 
remarkable  of  all,  and  that  which  possesses  the  most  important  physi- 
ological properties  in  the  animal  body,  is  the  red  coloring  matter  of  the 
blood.  It  appears  to  be  analogous  in  many  respects  to  the  green  matter 
of  leaves  and  leaflike  organs  in  the  vegetable  world.  Each  of  these  two 
coloring  matters  is  the  most  abundant  and  widely  diffused  in  its  own 
kingdom,  and  is  distinguished  by  the  identity  of  its  characters  in  many 
different  species  of  animals  and  plants  respectively.  While  the  red 
coloring  matter  of  the  blood,  on  the  one  hand,  is  the  agent  by  which 
oxygen  is  absorbed  and  distributed  in  the  animal  body  ;  on  the  other,  it 
is  the  green  coloring  matter  of  plants  by  which  carbonic  acid  and  water 
are  decomposed  and  oxygen  set  free  in  the  act  of  vegetation.  It  is 
believed  by  many  that  all  the  coloring  matters  of  the  body,  in  man  :iml 
the  vertebrate  animals,  are  derived  by  transformation  from  the  coloring 
matter  of  the  blood  ;  and  although  we  have  no  complete  proof  that  this 
is  true  in  all  cases,  yet  it  is  evident  that  these  substances  have  a  close 
physiological  relation  with  each  other,  perhaps  as  distinct  and  mil  as 
that  between  the  various  members  of  the  albuminous  or  saccharine 

groups. 

92 


COLORING    MATTERS. 


The  organic  coloring  matters  may  be  conveniently  removed  from 
liquids  containing  them  by  the  action  of  animal  charcoal;  that  is, 
carbon  derived  from  the  imperfect  combustion  of  animal  substances. 
If  a  fluid  containing  either  of  the  coloring  matters  be  mixed  with  a 
sufficient  quantity  of  this  charcoal  and  filtered,  the  filtered  fluid  will 
pass  through  colorless.  Albuminous  substances  are  also  retained  upon 
the  filter  when  treated  with  animal  charcoal ;  while  glucose  and  other 
crystallizable  and  saline  matters  pass  through  freely  in  solution. 

The  animal  coloring  matters  most  distinctly  recognized  are  those  of 
the  blood,  the  blackish-brown  tissues,  the  bile,  and  the  urine. 


1.  Hemoglobine, 

This  is  the  coloring  matter  of  the  red  globules  of  the  blood,  the 

ost   abundant   and  important   substance   belonging   to   this  group. 
It   forms   much   the    largest 

proportion  of  the  solid  ingre-  ^IG*  12- 

dients  of  the  dried  blood- 
globules,  and  amounts  to 
from  25  to  30  per  cent,  of 
their  weight  in  the  fresh 
condition.  It  is  also  found, 
in  much  smaller  quantity,  in 
the  substance  of  the  muscu- 

r  tissue,  of  which  it  forms 

e    coloring    principle.      It 

ystallizes    in  well   marked 

rms,  which  vary  somewhat 
different  species  of  ani- 
mals ;  but  are  all,  so  far  as 
known,  either  rhombic  or 
hexagonal  tables  or  prisms. 
It  is  soluble  in  water,  in  very 
dilute  alcohol,  and  in  dilute 

solutions  of  albumen,  of  the  alkalies,  and  their  carbonates,  and  of 
sodium  and  ammonium  phosphates.  It  is  insoluble  in  strong  alcohol, 
in  ether,  and  in  the  volatile  and  fatty  oils.  In  almost  every  condition 
it  is  readily  decomposed.  According  to  Preyer,*  crystals  which  have 
been  thoroughly  dried  at  a  temperature  below  the  freezing-point  become, 
after  a  time,  decomposed,  and  lose  their  color  and  solubility,  even  at 
inary  temperatures.  A  watery  solution  of  hemoglobine  kept  at  any 

mperature  above  the  freezing-point  of  water  becomes  altered  in  the 

urse  of  twenty-four   hours,  and  if  heated  to   64°  C.  it   is   at   once 
decomposed. 

Hemoglobine,  when  crystallized,  presents  the  bright  red  color  of 
arterial  blood.     It  is  distinguished  beyond  all  other  known  ingredients 


HEMOGLOBINE  CRYSTALS  ;  from  human  blood. 
(Funke.) 


*  Die  Blutkrystalle.     Jena,  1871,  p.  58. 


94  PHYSIOLOGICAL    CHEMISTRY. 

of  the  body,  by  its  capacity  for  absorbing  oxygen,  which  it  retains  in 
the  form  of  a  loose  combination.  According  to  the  average  result  of 
various  experiments  one  gramme  of  hemoglobine,  in  watery  solution, 
will  absorb  1.27  cubic  centimetres  of  oxygen.  It  is  again  deprived  of 
its  superabundant  oxygen  under  the  influence  of  diminished  pressure, 
heat,  or  the  continued  displacing  action  of  hydrogen  or  nitrogen.  Its 
hue  varies  according  to  these  two  conditions,  being  bright  red  in  the 
former  case,  dark  red  or  purple  in  the  latter.  It  is  therefore  known 
under  two  different  forms;  namely,  that  of  "  oxyhemoglobine,"  con- 
taining its  full  quota  of  loosely  combined  oxygen,  and  that  of  "  reduced 
hemoglobine,"  in  which  the  surplus  oxygen  has  been  removed.  Its 
presence,  in  either  one  or  the  other  of  these  conditions,  is  the  cause  of 
the  color  of  arterial  and  venous  blood. 

Spectrum  of  Hemoglobine. — All  transparent  coloring  matters,  when 
viewed  by  transmitted  light,  absorb  or  arrest  certain  portions  of  the 
luminous  ray  and  allow  others  to  pass.  The  transmitted  beam,  there- 
fore, appears  colored,  because  only  a  part  of  the  original  white  light 
reaches  the  eye.  If,  after  passing  through  a  colored  solution,  the 
luminous  ray  be  analyzed  into  its  spectrum  by  means  of  a  prism,  as  in 
the  spectroscope,  it  can  then  be  seen  exactly  what  colors  have  been 
allowed  to  pass  the  solution,  and  what  have  been  retained  by  absorption. 
Wherever  a  color  has  been  absorbed  or  arrested,  its  place  in  the  spec- 
trum is  occupied  by  a  dark  band.  Such  a  band  occurring  in  the 
spectrum  of  any  colored  substance,  is  called  an  "  absorption  band,"  and 
becomes  a  distinguishing  feature  in  the  spectrum  of  that  substance. 

The  spectrum  of  hemoglobine,  in  an  aerated  solution,  is  distinguished 
by  two  separate  absorption  bands.  The  first  is  a  comparatively  nar- 
row, dark,  and  well-defined  band  situated  in  the  yellow,  a  little  to  the 
right  of  the  line  D.  The  second  is  a  wider,  fainter,  and  more  diffused 
band,  at  the  commencement  of  the  green,  and  a  short  distance  to  the 
left  of  the  line  E.  Both  bands  are,  therefore,  contained  in  the  space 
between  the  lines  D  and  E.  Beyond  E  the  green  and  blue  of  the  spec- 
trum are  visible,  but  the  light  diminishes  gradually  and  disappears  near 
the  end  of  the  blue,  so  that  the  indigo  and  violet  parts  are  completely 
dark.  Fresh  blood,  diluted  with  water,  will  give  the  same  appearance. 

If  the  solution  be  concentrated,  or  viewed  in  a  very  thick  layer,  it 
is  too  opaque  for  spectroscopic  examination,  and  may  shut  off  all  the 
light  of  the  spectrum  except  a  little  of  the  red  and  orange;  if  too 
dilute,  it  will  fail  to  exhibit  its  distinguishing  characters.  A  solu- 
tion of  a  certain  strength,  which  allows  abundance  of  light  to  pa<s, 
and  is  yet  sufficient  to  cause  its  absorption  at  particular  points,  is 
best  suited  for  examination.  With  pure  hemoglobine,  according  to 
Preyer,  a  solution  of  about  1.5  parts  per  thousand  gives  the  most 
marked  results.  With  fresh  blood,  if  one  volume  of  the  defibrinated 
blood  be  diluted  with  one  hundred  volumes  of  water,  and  the  mixture 
viewed  in  a  layer  of  one  centimetre,  all  the  charaeteristie  traits  of  the 
spectrum  will  lie  distinctly  shown.  (  Fi#.  13,  I.) 


COLORING    MATTERS. 


95 


These  characters  form  a  very  delicate  test  for  the  coloring  matter  of 
blood.  Preyer  has  found  that  with  a  solution  of  pure  hemoglobine  in 
water,  of  4  parts  per  ten  thousand,  the  absorption  bands  may  still  be 
seen,  though  the  second  one  is  very  faint ;  and  according  to  Hoppe- 
Seyler,  a  solution  of  one  part  in  ten  thousand  will  allow  them  to  be 
recognized  if  viewed  in  a  layer  one  centimetre  in  thickness.  Fresh 
dog's  blood,  if  diluted  with  1,000  parts  of  water,  and  viewed  in  a  layer 
£f  3  centimetres'  thickness,  will  show  a  spectrum  in  which  both  absorp- 
tion bands  are  distinctly  perceptible  though  not  very  strong.  If  diluted 
with  10,000  parts  of  water,  and  viewed  in  a  layer  of  4.5  centimetres, 
the  first  band  is  still  visible,  though  very  faint ;  the  second  is  imper- 
ceptible. 

The  condition  of  hemoglobine,  in  regard  to  its  absorption  of  oxygen, 
has  a  marked  effect  on  its  spectroscopic  characters.  The  spectrum 
with  two  absorption  bands,  above  described,  is  that  of  hemoglobine 
which  has  absorbed  all  the  oxygen  which  it  is  capable  of  holding  in 
loose  combination.  If  this  oxygen  be  removed,  the  color  of  the 
solution  is  modified  and  its  spectrum  changes.  The  coloring  matter 
is  no  longer  oxyhemoglobine,  but  has  become  reduced  hemoglobine ; 
and  its  spectrum,  instead  of  two  absorption  bands,  shows  but  one, 
comparatively  wide  and  ill-defined,  the  darkest  part  of  which  occupies 

FIG.  13. 


T.  Spectrum  of  Oxyhemoglobine. 

II.  Spectrum  of  Reduced  Hemoglobine. 

y  the  space  formerly  intervening  between  the  two.  At  the  same 
me  the  dim  borders  of  the  obscured  portion  shift  toward  the  left ;  so 
ihat  the  orange  in  the  neighborhood  of  the  line  D  is  less  brilliant  than 
before,  while  nearly  the  whole  of  the  green  becomes  visible  to  the  left 
of  the  line  E.  The  blue  is  also  extended  a  little  toward  the  right. 
(Fig.  13,  II.) 

The  coloring  matter  of  the  blood  may  be  deprived  of  its  loosely 
combined  oxygen  by  evacuation  with  the  air-pump,  treatment  with  a 
current  of  hydrogen  or  nitrogen,  the  addition  of  deoxidizing  agents,  or 


96  PHYSIOLOGICAL     CIIKMI8TRY. 

by  keeping  the  blood  or  its  solutions  protected  from  the  access  of  air. 
The  last  method  is  most  easily  applied.  If  a  solution  of  fresh  blood, 
of  a  bright  scarlet  color,  which  yields  a  spectrum  with  the  absorption 
bands  of  oxyhemoglobine  fully  developed,  be  inclosed  in  a  securely 
stopped  test-tube,  the  whole  of  which  it  completely  fills,  and  kept  in 
this  condition  for  twenty-four  or  forty -eight  hours,  the  hemoglobin*  •  sit 
the  end  of  that  time  will  have  lost  its  surplus  oxygen,  and  if  placed 
before  the  spectroscope,  the  solution  will  show  a  spectrum  with  tin- 
single  absorption  band  of  reduced  hemoglobine.  If  the  test-tube  be 
now  opened,  the  solution  transferred  to  a  larger  vessel,  and  shaken  up 
for  a  few  seconds  with  atmospheric  air,  its  bright  color  returns,  the 
single  absorption  band  disappears  from  its  spectrum,  and  the  two 
absorption  bands  of  oxyhemoglobine  again  become  visible. 

The  spectroscopic  characters  of  hemoglobine  are  of  value  in  showing 
that  this  substance,  as  extracted  in  the  crystalline  form,  is  identical 
with  the  normal  coloring  matter  of  the  fresh  globules.  A  solution  of 
crystallized  hemoglobine  gives  the  same  spectrum  with  solutions  of 
fresh  blood  or  with  the  dried  globules.  The  blood,  while  still  circulat- 
ing in  the  vessels,  may  also  be  made  to  exhibit  the  same  appearances. 
If  a  spectroscope  eye-piece  with  two  prisms  be  attached  to  the  body  of 
a  microscope  in  such  a  way  that  two  spectra  may  be  seen  in  the  field, 
one  above  another,  one  formed  by  the  light  coming  through  the  body 
of  the  instrument,  the  other  by  that  coming  through  a  lateral  opening 
in  the  eye-piece ;  and  if  the  mesentery  of  a  living  frog  be  placed 
before  the  objective  of  the  microscope,  while  a  solution  of  human  blood 
is  placed  at  the  lateral  opening,  it  will  be  seen  that  the  absorption  bands 
in  the  two  spectra  correspond  exactly  with  each  other. 

The  hemoglobine  from  different  animals  varies  somewhat  in  the  form 
of  its  crystals,  in  their  degree  of  solubility  in  water,  and,  according 
to  several  analyses,  in  the  exact  percentage  of  its  constituent  elements. 
But  its  spectroscopic  characters  are  remarkably  invariable ;  and  their 
immediate  connection  with  its  essential  physiological  property,  namely, 
the  absorption  and  discharge  of  oxygen,  shows  them  to  be  the  most 
important  marks  for  it>  identification.  By  this  means  the  existence 
of  hemoglobine  in  the  blood-globules  has  been  demonstrated  in  such 
(lifl'erent  animals  as  the  d6g,  fox,  cat,  horse,  sheep,  pig,  lion,  cougar, 
baboon,  bat,  hedge-hog,  rat,  guinea-pig,  squirrel,  mole,  goose,  pigeon, 
lark,  owl,  crow,  lizard,  python,  tortoise,  frog,  carp,  perch,  herring,  and 
pike.  It  has  been  discovered,  in  all,  in  22  species  of  mammalians,  7 
birds,  f>  reptiles,  and  1:2  fish;  and  exists  in  every  species  of  veriebr;ii< 
animal  which  lias  lieen  examined  for  that  purpose.  Even  in  several 
invertebrate  species,  where  the  blood  is  of  a  red  color,  although  exhibit- 
ing no  distinct  globules,  it  is  found  to  contain  hemoglobine  in  a  state 
of  solution.  IVeyer  found  that  the  red  circulating  fluid  of  the  earth- 
worm, when  examined  by  the  spectroscope,  yields  a  spectrum  with 
two  absorption  bands  identical  with  those  of  human  hemoglobine.  Ji 


the 

ace 
hui 


COLORING    MATTERS.  97 

has  also  been  discovered  in  the  blood  of  the  pond-snail,  the  horse-leech, 
and  the  fresh-water  shrimp. 

Functional  Activity  and  Changes  of  Hemoglobine  in  the  Body. — 
Hemoglobine  is  the  most  active  of  all  the  coloring  matters  in  the 
animal  system.  It  absorbs  oxygen  from  the  air  in  the  lungs,  and  thus 
provides  an  incessant  supply  for  the  whole  body.  But  this  absorption 
is  not  a  process  of  oxidation.  The  oxyhemoglobine  holds  its  oxygen 
in  loose  combination,  and  readily  parts  with  it  in  the  general  circula- 
tion, returning  to  the  state  of  reduced  hemoglobine  in  the  venous  blood. 
Each  of  these  two  properties  is  equally  important  with  the  other,  for  it 
is  by  this  means  that  the  oxygen  of  the  lungs  finds  its  way  into  the 
system  at  large. 

A  marked  feature  in  the  chemical  constitution  of  hemoglobine  is  that 
it  contains  iron.  This  fact  is  the  more  important  because  it  is  the  only 
substance  in  the  animal  body,  excepting  hair,  which  contains  iron  in 
any  considerable  amount,  and  because  iron  is  also  requisite  for  the  for- 
mation of  the  green  coloring  matter  of  plants.  Experiment  has  shown 
that  without  iron  vegetation  cannot  go  on ;  and  there  is  reason  to 
believe  that  it  is  equally  essential  to  the  constitution  of  the  animal 
coloring  matter,  and  thus  indirectly  to  the  general  nutrition  of  the 
animal  body.  It  is  present  in  hemoglobine,  in  all  probability,  not  in 
the  form  of  a  distinct  oxide,  but  directly  combined,  like  sulphur,  with 
the  carbon,  hydrogen,  nitrogen,  and  oxygen  which  form  the  remainder 
f  its  substance. 

One  thousand  parts  of  hemoglobine  contain  4.2  parts  of  iron ;  and, 

ording  to  the  average  results  obtained  by  different  observers,  healthy 
uman  blood  contains,  per  thousand  parts,  123.4  parts  of  hemoglobine, 
and  0.52  parts  of  iron.  The  human  body,  according  to  the  lowest 
authentic  estimate,  contains  8  per  cent,  of  its  weight  of  blood,  which 
would  give,  for  a  man  weighing  65  kilogrammes,  2.71  grammes  of  iron 
in  the  blood  of  the  whole  body. 

The  iron  of  the  hemoglobine  passes  out  by  the  bile  and  the  urine, 
both  of  which  contain  traces  of  its  presence.  It  is  also  contained  in 
the  hair,  where  it  forms  nearly  t  per  cent,  of  the  incombustible  ingre- 
dients. It  is  supplied  to  the  body  by  ordinary  food,  in  which  it  is 
always  present  in  appreciable  amount.  Since  hemoglobine  exists  to 

me  extent  in  the  muscular  tissue,  it  will  be  present  in  a  more  or  less 
tered  form,  but  still  containing  iron,  in  most  kinds  of  animal  food. 

ccording  to  the  analyses  of  Moleschott,  500  grammes  of  beef  (about 
one  pound  avoirdupois)  will  contain  0.035  gramme  of  iron ;  and  it  is 
bund  in  even  larger  proportion  in  rye,  barley,  oats,  wheat,  peas,  and 
•cially  in  strawberries.  As  the  quantity  of  this  substance  discharged 
daily  in  the  urine  and  the  bile  is  so  small,  we  must  regard  the  greater 
portion  of  that  which  passes  through  the  system  as  used  in  the  growth 
of  the  hair;  and  a  very  moderate  amount  in  the  food  is  sufficient  for 
the  requirements  of  nutrition. 


al 

: 

Ollv, 

foun 

",T 


98  PHYSIOLOGICAL    CHEMISTRY. 

2.  Melanine. 

In  all  the  dark -colored  tissues  of  the  body,  in  the  choroid  coat  of 
the  eye,  the  rote  Malpighi  of  the  skin  in  the  black  and  brown  races, 
and  in  individuals  of  dark  complexion,  in  the  hair,  and  in  the  substance 
of  melanotic  tumors,  there  exists  a  coloring  matter  known  as  melanine. 
When  isolated  or  collected  in  compact  masses,  it  is  of  a  very  dark 
blackish-brown  color  ;  but  by  its  mixture,  in  different  proportions,  with 
other  colorless  or  ruddy  semi-transparent  ingredients  of  the  tissue.-,  it 
may  produce  all  the  varying  grades  of  hue,  from  light  yellowish-brown 
to  nearly  absolute  black.  It  is  deposited  in  the  substance  of  cells  in 
the  form  of  minute  granules,  and  is  usually  more  abundant  in  the 
immediate  neighborhood  of  the  nucleus  than  near  the  edges  of  the  cell. 
A  substance  regarded  as  melanine  has  also  been  found  by  several 
observers  in  certain  morbid  deposits  under  the  crystalline  form,  espe- 
cially as  flat  rhombic  tablets  with  acute  angles. 

The  elementary  analyses  of  melanine  derived  from  different  sources 
do  not  exactly  correspond  with  each  other,  although  they  approximate 
within  moderate  limits.  As  the  average  result  of  analyses  collected 
by  Hoppe-Seyler,*  it  contains,  freed  from  ashes,  the  following  pro- 
portions, by  weight,  of  carbon,  hydrogen,  nitrogen,  and  oxygen. 

COMPOSITION  OF  MELAXINE. 

Carbon 54.39 

Hydrogen 5.08 

Nitrogen 11.17 

Oxygen 29.36 

100.00 

Repeated  observations  show  that  it  also  contains  iron,  which  has 
been  found  by  Lehmann  in  the  proportion  of  2.5  parts  per  thousand. 

Melanine  is  insoluble  in  water,  alcohol,  ether,  and  solutions  of  the 
organic  and  mineral  acids.  Boiling  solutions  of  potassium  hydrate 
dissolve  it  without  change  of  color,  but  its  color  is  destroyed  by  chlorine. 

Melanine  is  supposed  to  be  produced  by  metamorphosis  from  the 
hemoglobine  of  the  blood.  The  fact  that  it  contains  iron  id\ 
certain  probability  to  this  view ;  and  it  is  a  repeated  observation  that 
black  or  blackish  staining  of  the  tissues  sometimes  appears  in  and 
around  old  spots  of  congestion  or  ecchymosis.  It  also  forms  the  prin- 
cipal coloring  matter  of  the  hair,  which  probably  contains  most  of  tin- 
iron  derived  from  destructive  assimilation  of  the  blood-globules. 

3.  Bilirubine,  C18H18N,O,. 

The  red  or  orange-red  coloring  matter  of  the  bile.  This  substance 
has  been  designated,  by  different  writers,  under  the  various  names  of 
IJilipha'in,  Bilifulvinc,  Ileniatoidine,  and  rholepyrrhine.  It  is  formed 


">;~  I I:iM(!l>iicii  »KT  Physiologiach  mul  Pathologisch-Chenaischen  Analyst.'.      Berlin, 
.  177. 


COLORING    MATTERS.  99 

in  the  liver,  and  may  be  extracted  from  its  tissue  in  a  pure  form. 
From  the  liver  cells  it  is  taken  up  by  the  biliary  ducts  and  mingled 
with  the  other  ingredients  of  the  bile.  It  is  crystallizable,  soluble  in 
chloroform,  less  so  in  alcohol,  and  slightly  soluble  in  ether.  It  is  readily 
soluble  in  alkaline  liquids,  but  quite  insoluble  in  pure  water.  In  the 
crystallized  form  it  is  red ;  in  the  amorphous  condition,  orange  ;  and  in 
solution,  reddish-brown  or  yellow,  according  to  the  degree  of  concen- 
tration. According  to  Hoppe-Seyler,  it  gives  a  perceptible  yellow 
color  when  viewed  in  a  layer  1.5  centimetre  in  thickness,  even  if  dis- 
solved in  500,000  times  its  weight  of  fluid. 

Solutions  of  bilirubine  exhibit  a  well-marked  reaction  with  nitroso- 
nitric  acid,  known  as  "  Gmelin's  bile  test."  If  such  a  solution  be 
treated  with  a  small  quantity  of  nitric  acid,  tinged  with  nitrous  acid, 
a  series  of  colors  is  presented  in  the  following  order:  green,  blue, 
violet,  red,  and  finally  a  dingy  yellow.  These  colors  are  produced  by 
transformation  of  the  bilirubine,  and  represent  successive  degrees  of 
its  oxidation.  The  reaction  is  a  very  sensitive  one,  and,  according  to 
Hoppe-Seyler,  will  produce  a  visible  result  in  solutions  containing  only 
one  part  in  70,000. 

Bilirubine  is  generally  regarded  as  derived  from  hemoglobine.     The 
reasons  for  this  opinion  are :  First,  its  reddish  color,  somewhat  simi- 
lar to  that  of  diluted  blood.     Secondly,  it  has  been  found  in  various 
parts  of  the  body,  in  old  bloody  extravasations,  evidently  produced 
from  an  alteration  of  the  blood  upon  the  spot.     When  found  under 
these  circumstances,  it  was  formerly  known  as  hematoidine.    Thirdly, 
if  the  blood-globules  be  made  to  assume  a  liquid  form  by  alternately 
freezing  and  thawing  a  portion  of  freshly  drawn  blood,  and  this  blood 
then  re-injected  into  the  blood-vessels,  the  operation  is  followed  by  a 
discharge  of  bilirubine  in  the  urine.     If  hemoglobine  be,  in  fact,  nor- 
mally transformed  into  bilirubine,  its  iron  and  sulphur  must  enter  into 
>me  other  combination,  as  neither  of  these  elements  exists  in  the 
)loring  matter  of  the  bile.     Bilirubine,  if  exposed  to  the  air  in  alkaline 
)lution,  becomes  oxidized  and  assumes  a  green  color,  being  converted 
ito  the  following  closely  related  substance,  biliverdine. 

4.  Biliverdine,  C16H20N2O5. 

In  addition  to  bilirubine,  the  bile  contains  a  green  substance,  known 
biliverdine ;  and  the  varying  tint  of  different  specimens  of  bile 
spends  on  the  proportion  in  which  the  two  coloring  matters  are  pres- 
it.  In  man  and  the  carnivorous  and  omnivorous  animals,  the  bile  is 
ronze,  brown,  yellowish,  or  orange,  owing  to  the  presence  of  biliru- 
bine ;  while  in  the  ox,  sheep,  rabbit,  and  vegetable  feeders  generally, 
it  presents  a  strong  green  or  greenish  color,  due  to  the  comparative 
abundance  of  biliverdine.  Biliverdine  is  insoluble  in  water,  ether,  and 
chloroform,  readily  soluble  in  dilute  alkaline  solutions  and  in  alcohol. 
It  is  also  soluble  in  glacial  acetic  acid,  and  is  deposited  from  the  evap- 
orated solution  in  a  form  of  imperfect  crystallization.  It  is  often 


100 


PIT  Y  BIOLOGICAL    CHEMISTRY. 


found  in  human  gall  stones,  and  in  the  dog  is  abundantly  deposited 
along  the  edges  of  the  placenta. 

The  spectrum  of  biliverdine  is  marked  by  a  very  distinct  and  dark 
absorption  band  in  the  red,  at  the  situation  of  the  line  C,  extending 
thence  to  the  left  toward  the  line  B.  Its  width  increases  with  the 
thickness  of  the  layer  of  fluid  examined,  and  when  this  exceeds  a  cer- 
tain limit  the  whole  of  the  red  disappears.  The  band  rarely  reaches 
the  situation  of  the  line  B,  and  seldom  or  never  passes  beyond  it,  with- 
out extinguishing  at  the  same  time  all  the  red  light  of  the  spectrum. 
In  layers  of  green  bile,  two  or  three  centimetres  in  thickness,  it  is 
quite  dark,  often  almost  black,  while  the  red  on  each  side  of  it  is  still 
very  brilliant. 

As  a  rule,  the  intensity  of  the  absorption  band  at  C  is  in  proportion 
to  the  preponderance  of  green  in  the  color  of  the  bile.  Though  easily 
seen,  in  comparatively  thin  layers,  in  specimens  of  a  pure  green  or 
a  decided  greenish-olive  color,  it  is  less  perceptible  in  those  of  a 
yellowish,  yellowish-brown,  or  olive-brown  tint.  But  if  a  specimen 

FIG.  14. 


SPECTRUM  OF  GREKN  (.SHEEP'S)  BII.K. 

of  reddish  or  yellowish-brown  bile,  which  does  not  show  the  band 
distinctly,  be  turned  green  by  the  addition  of  a  few  drops  of  an  iodine 
solution,  the  band  at  C  at  once  becomes  visible,  often  to  a  very  marked 
degree.  It  is,  therefore,  no  doubt  the  characteristic  absorption  band 
of  biliverdine.  (Fig.  14.) 

There  are  two  other  absorption  bands  in  the  spectrum  of  bile,  le^s 
constant  and  much  less  distinct  than  that  at  the  line  C.  One  of  them, 
very  dim  and  ill-defined,  is  situated  at  the  junction  of  the  orange  and 
yellow,  immediately  to  the  left  of  the  line  I),  occupying  about  the  last 
third  of  the  space  between  C  and  D.  The  remaining  band  is  much  nar- 
rower than  either  of  the  others,  but  somewhat  more  distinct  than  the 
second.  It  is  situated  in  the  yellow,  at  about  one-third  the  distamv 
between  D  and  E.  The  last  two  bands  are  more  frequently  visible  in 
sheep's  bile  than  in  that  of  other  animals ;  but  all  three  may  be  some- 
times seen  in  a  watery  solution  of  desiccated  ox-bile,  which  lias  been 
kept,  in  the  form  of  a  dry  powder,  for  several  years. 

The  spectrum  of  bile  also  exhibits  a  remarkable  diminution  in 
intensity  of  the  nranire  mid  yellow  colors.  The  situation  of  the  second 


COLORING    MATTERS.  101 

absorption  band,  at  the  junction  of  these  colors,  will  account  for  a  part 
of  this  diminution  ;  but  the  spectrum  is  also  very  dim  in  the  space 
between  the  second  and  third  absorption  bands,  where  the  normal 
spectrum  of  solar  light  is  brightest.  This  is  the  place  naturally  occu- 
pied by  yellow,  but  in  the  great  majority  of  cases,  in  the  spectrum  of 
bile,  there  is  no  pure  yellow  perceptible,  and  but  little  or  no  orange. 
The  situation  of  these  two  colors  is  encroached  upon  by  the  red  and 
green  respectively  ;  and  in  not  a  few  instances,  as  the  spectrum  termi- 
nates before  the  commencement  of  the  blue,  the  only  colors  really  per- 
ceptible in  it  are  red  and  green.  The  line  C  in  the  normal  spectrum 
is  situated  at  the  junction  of  the  red  and  orange,  and  yet  the  principal 
absorption  band  at  this  point,  when  viewed  in  the  spectrum  of  bile, 
appears  to  be  situated  entirely  in  the  red,  owing  to  this  color  taking 
the  place  of  the  orange  on  the  right  of  the  line  C.  This  peculiarity 
shows  itself  in  the  spectrum  of  bile,  whether  the  color  of  the  specimen 
be  greenish  or  yellowish-brown. 

There  is  another  spectroscopic  feature  in  bile,  due  to  its  containing 
more  or  less  of  two  different  coloring  matters. 

If  a  tolerably  thick  layer  of  bile  be  placed  before  the  spectroscope, 
and  the  slit  of  the  instrument  gradually  opened,  the  first  light  which 
appears  in  the  spectrum  is  usually  a  green  light,  in  the  latter  half  of 
the  space  between  D  and  E.  On  continuing  to  increase  the  size  of  the 
opening,  if  the  bile  be  deeply  colored,  the  next  to  appear  is  a  red  light, 
at  the  extreme  end  of  the  spectrum  between  A  and  B ;  in  less  concen- 
trated specimens  the  red  light  may  show  itself  simultaneously  on  both 
sides  of  the  absorption  band  at  C.  Afterward  the  green  light  extends 

Kther  toward  the  left  until  the  spectrum  is  complete.  The  order  in 
ich  these  appearances  follow  each  other  depends  upon  the  relative 
intity  of  bilirubine  or  biliverdine. 

There  is  reason  to  believe  that  biliverdine  is  formed  from  bilirubine 
by  a  process  of  hydration  and  oxidation,  the  elements  of  water  entering 
at  the  same  time  into  combination.  The  nature  of  this  change  is  shown 
by  the  following  formula : 

Bilirubine.  Biliverdine. 

C16H18N203  +  ILO  +  O  =  CuH^N  A. 

The  prompt  conversion  of  the  color  of  ruddy  or  reddish-brown  bile 
into  green  by  the  action  of  various  oxidizing  agents,  or  even  by  ex- 
posure to  the  air,  and  the  evident  chemical  relationship  between  the 
<o  substances,  leave  no  doubt  that  this  is  the  origin  of  biliverdine. 
th  bilirubine  and  biliverdine  are  discharged  with  the  bile  into  the 
oaentary  canal,  where  they  become  undistinguishable  toward  the 
lower  end  of  the  small  intestine.     Beyond  that  point  they  are  replaced 
by  the  brown  coloring  matter  of  the  feces,  and  are  finally  discharged 
from  the  body  under  this  form. 

5.  Urochrome. 

The  coloring  matter  of  the  urine  has  been  repeatedly  studied,  but 


102  PHYSIOLOGICAL    CHEMISTRY. 

thus  far  with  only  partial  success.  The  substances  which  have  been 
extracted  from  the  urine  by  various  methods,  as  representing,  more  or 
less  exactly,  its  natural  coloring  matter,  are  known  by  the  names  of 
Urochrome,  Urosine,  Urosacine,  Hemapha^ine,  Urohematine,  Uroxan- 
thine,  Urobiline,  and  Hydrobilirubine.  Most  of  them  are  probably 
modifications  of  the  same  substance,  variously  altered  by  the  methods 
of  extraction,  or  obtained  in  different  grades  of  purity.  The  fresh. 
normal  urine  has  a  light  yellowish  or  amber  color,  while  specimens  of 
unusually  high  specific  gravity,  and  particularly  specimens  of  febrile 
urine,  often  exhibit  a  distinct  reddish  hue.  Normal  urine,  which,  when 
fresh,  is  only  amber-colored,  will  often  acquire,  by  exposure  to  the  air, 
a  tinge  of  red.  The  substance  obtained  by  Thudichum,*  and  called  by 
him  urochrome,  is  precipitable  from  the  urine  by  various  metallic  salts. 
It  has  not  yet  been  produced  in  a  crystalline  form.  It  is  soluble  in 
water  and  in  ether,  but  only  slightly  soluble  in  alcohol.  Its  watery 
solution  has  a  yellowish  color,  which,  on  standing,  becomes  red. 
Urohematine  (Harley)  is  nitrogenous  in  composition,  and  contains 
iron.f  It  is  insoluble  in  pure  water,  but  soluble  in  the  fresh  urine,  as 
well  as  in  ether,  chloroform,  and  alcohol.  The  substance  termed  Uro- 
biline (Jaffe)  was  so  named  to  indicate  its  derivation  from  the  coloring 
matter  of  the  bile.  -  It  is  identical  with  hydrobilirubine  (Maly), 
which  is  produced  from  bilirubine  by  hydration  and  deoxidation  by 
means  of  sodium-amalgam.  The  change  which  takes  place  in  this 
process  is  as  follows : 

Bilirubine.  Urobiline. 

2(018H18N203)  +  2(H30)— 0  =  032H40N407. 

Urobiline  is  soluble  in  alcohol,  ether,  and  chloroform.  Its  solutions 
have  a  brownish-yellow  color,  and,  by  dilution,  become  first  yellow, 
and  lastly  faint  rosy-red.  It  was  found  by  Jaffe  J  in  many  eases  in 
human  urine,  where  it  was  recognized,  after  partial  extraction  and 
purification,  by  its  spectroscopic  properties;  showing  an  absorption 
band  at  the  junction  of  the  green  and  the  blue,  between  the  lines  K 
and  F.  But  the  same  observer  found  that  fresh  urine,  not  subjected  to 
chemical  manipulation,  would  often  present  no  indication  of  urobiline. 
If  secluded  from  the  atmosphere,  it  would  remain  light-colored ;  but  if 
exposed  to  the  air  from  two  to  twelve  hours,  it  would  become  darker 
in  hue,  and  at  the  same  time  would  show,  by  the  spectroscope,  signs 
of  urobiline.  This  substance  consequently  is  not  now  regarded  as  the 
normal  coloring  matter  of  the  urine,  but  as  a  product  of  its  alteration. 

It  is  evident,  however,  "that  the  urine  contains  a  coloring  matter, 
derived  in  all  probability  from  the  bile,  which  gives  to  it  its  well-known 
amber  tint.  This  substance  is  liable  to  be  changed  under  the  influence 
of  oxidation,  and  to  assume  in  that  condition  a  more  or  less  distinctly 


*  British  Medical  Journal.     London,  Nov.  5,  IM'.  1. 

fHarley,  The  Urine  and  its  Derangi-iiu-nts.      Philadelphia,  IST'J.  (>.  !>7. 

JArchiv  fur  pathologische  Anatomic  und  Physiologic,  18G9,  Band  xlvii.,  p.  405. 


COLORING    MATTERS.  103 

red  color.  Such  a  modification  certainly  takes  place  outside  the  body, 
and  it  may  also  occur  within  the  system,  giving  rise  to  the  varying 
proportions  of  red  in  the  color  of  the  urine  under  different  healthy  and 
diseased  conditions. 

6.  Chlorophylle. 

This  is  the  green  coloring  matter  of  plants.  It  is  more  widely 
diffused  than  any  other  coloring  matter  in  the  vegetable  world,  and  it 
apparently  constitutes  the  coloring  principle  of  all  the  green  parts  of 
the  higher  plants  without  exception.  It  has  been  obtained  by  Gautier* 
in  the  crystalline  form,  as  flattened,  isolated,  or  radiating  needles,  of  a 
softish  consistency  and  an  intensely  green  color;  afterward,  by  ex- 
posure to  light,  they  become  yellowish-green,  then  brownish-green, 
and  are  lastly  decolorized.  Its  composition  is  as  follows : 

COMPOSITION  OF  CHLOROPHYLLS. 

Carbon 73.97 

Hydrogen 9.80 

Nitrogen 4.15 

Oxygen 10.33 

Ash 1.75 

100.00 

Its  incombustible  residue  consists  mainly  of  alkaline  phosphates. 
It  is  completely  destitute  of  iron. 

The  similarity  of  chlorophylle  to  biliverdine,  fully  recognized  by 

FIG.  15. 


5 


SPECTRUM  OF  CHLOROPHYLLE  IN  ALCOHOLIC  SOLUTION. 

autier  in  regard  to  some  of  its  chemical  reactions,  is  very  strongly 
marked  in  its  spectroscopic  characters.  The  principal  absorption 
nd  in  the  spectra  of  these  two  substances  is  identical  in  position 
d  appearance.  It  is  the  dark  band  sifuated  in  the  red,  extending 
from  the  line  C  toward  B.  (Fig.  15.)  In  an  alcoholic  solution  of 
chlorophylle,  extracted  from  green  grass  or  leaves,  there  are  three 
additional  bands,  less  prominent  than  the  former,  and  differing  from 
those  of  bile.  One  of  these  additional  bands  is  placed  at  the  edge  of 

*  Coraptes  Rendus  de  1'  Academic  des  Sciences.     Paris,  1879.    Tom. 
p.  861. 


104  PHYSIOLOGICAL    CHEMISTRY. 

the  orange,  between  C  and  D ;  another  at  the  beginning  of  the  green, 
on  the  left  of  E  ;  and  a  third,  wider  than  the  others,  but  very  faint  tmd 
ill-defined,  at  the  termination  of  the  green,  between  E  and  F.  In  the 
spectrum  of  chlorophylle,  the  yellow  of  the  spectrum  appears  in  its 
proper  place  and  with  nearly  its  natural  hue.  The  light,  also,  extends 
beyond  the  green,  throughout  the  blue,  and  a  little  into  the  com- 
mencement of  the  indigo. 

Chlorophylle  is  of  the  first  importance  in  vegetable  physiology,  as  it 
is  under  the  influence  of  this  substance,  and  that  of  the  solar  light, 
that  the  inorganic  ingredients  of  the  soil  and  the  atmosphere  are 
deoxidized  and  combined  to  form  a  carbo-hydrate.  The  process  of 
vegetation  proper,  that  is,  the  production  and  accumulation  of  organic 
material  in  the  form  of  starch,  sugar,  cellulose,  and  the  substance 
of  various  vegetable  tissues,  is  inseparably  dependent  on  the  action  of 
chlorophylle.  But  to  produce  this  effect,  the  chlorophylle  must  con- 
stitute a  part  of  the  living  vegetable  cell.  The  coloring  matter  alone, 
extracted  from  the  chlorophylle-holding  cells,  and  placed  under  all  other 
conditions,  such  as  air,  sunlight,  warmth,  and  moisture,  known  to  be 
essential  to  the  work  of  production,  is  incapable  of  forming  organic 
matter  out  of  water  and  carbonic  acid,  Its  function  is  not  that  of  a 
simple  chemical  reagent,  but  that  of  an  active  constituent  of  the  living 
organism. 

Chlorophylle  is  produced,  in  the  interior  of  the  vegetable  cell,  some- 
times as  a  uniformly  diffused  mass.  Usually,  however,  it  is  deposited 
in  rounded  grains,  frequently  arranged  in  definite  figures  or  patterns 
within  the  cell.  It  may  be  extracted  by  alcohol  or  ether,  and  retains 
its  green  color  when  in  solution  in  these  substances.  It  disappears 
previously  to  the  shedding  of  the  leaves,  when  they  cease  the  act  of 
vegetation,  and  is  usually  replaced  by  grains  of  a  red  or  yellowish 
color. 


CHAPTER    VI. 
CKVSTALLIZASLE  NITEOGENOUS    MATTERS. 

rilHE  fifth  and  last  group  of  bodily  ingredients  consists  of  a  number 
-L  of  colorless  substances,  which  resemble  the  albumenoids  in  con- 
taining nitrogen,  but  differ  from  them  in  being  crystallizable.  Many 
of  them  are  evidently  derived  from  the  albumenoids  by  retrograde 
metamorphosis,  being  discharged  from  the  system  as  products  of  excre- 
tion. Others  do  not  exhibit  this  character,  and  are  found  only  in  the 
permanent  tissues  or  the  internal  fluids.  Several  of  them,  though 
undoubtedly  of  importance  in  the  constitution  of  the  body,  are  still 
obscure  in  their  physiological  relations 

1.  Lecithine,  C44H90NPO9, 

From  AEX&OS,  the  yolk  of  egg,  in  which  substance  it  was  first  discovered. 
Lecithine  was  formerly  described  under  the  name  of  phosphorized  fat, 
owing  to  the  circumstance  that  one  of  the  products  of  its  decomposition 
is  phosphoglyceric  acid  (C3H9PO6).  It  is  not,  however,  a  fatty  sub- 
stance, since  it  contains  nitrogen,  and  otherwise  differs  from  the  fats. 
As  mingled  or  combined  with  other  animal  matters,  it  has  also  been 

own  by  the  name  of  "protagon."  Lecithine  is  of  very  wide  dis- 
ution  in  both  the  animal  and  vegetable  kingdoms,  occurring  in  the 
cereal  grains  and  leguminous  seeds,  and,  according  to  Hoppe-Seyler, 
in  the  cellular  juices  of  a  variety  of  plants.  It  is  found  in  the  blood, 
both  in  the  plasma  and  the  globules,  in  the  bile,  the  spermatic  fluid, 
the  yolk  of  egg,  and  particularly  in  the  brain,  spinal  cord,  and  nerves. 
In  the  plasma  of  the  blood,  it  is  in  the  proportion  of  0.4  part  per 
thousand,  and  in  the  fresh  substance  of  the  calf's  brain,  according  to 
the  analyses  of  Petrowsky,*  in  the  proportion  of  31  parts  per  thousand. 
Taking  into  account  the  watery  ingredients  of  the  brain,  lecithine  is 
about  equally  abundant  in  the  white  and  gray  substance ;  but  of  the 
solid  matters  alone,  it  constitutes  a  little  less  than  10  per  cent,  in  the 
white  substance,  and  rather  more  than  17  per  cent,  in  the  gray 
substance. 

Lecithine  obtained  from  either  of  these  sources  is  an  indistinctly 
crystallizable  substance,  of  waxy  consistency,  liquefying  at  a  gentle 
heat,  readily  soluble  in  alcohol,  less  so  in  ether,  and  to  some  extent  in 
chloroform  and  the  fatty  oils.  If  treated  with  water,  it  swells  into 
a  pasty  mass  without  dissolving,  and  gives  origin,  under  the  micro- 
scope, to  the  appearances  known  as  "myeline  forms;"  that  is,  a  great 

*  Archiv  fur  die  gesammte  Physiologic.     Bonn,  1873,  Band  vii.,  p.  101. 

105 


100  PHYSIOLOGICAL,    CHEMISTRY. 

variety  of  mucilaginous  or  oily  looking  drops  and  filaments,  of  double 
contour,  which  exude  from  the  edges  of  the  mass,  and  remain  separate 
and  insoluble  ;  resembling  the  microscopic  forms  produced  under  simi- 
lar circumstances  from  the  "myeline,"  or  medullary  layer  of  nerve 
fibres.  It  is  readily  decomposed  on  standing,  either  in  solution  or  in  a 
state  of  watery  imbibition,  acquiring  an  acid  reaction.  Decomposition 
is  also  effected  by  acids  or  alkalies.  By  boiling  with  baryta-water 
it  suffers  a  characteristic  alteration,  giving  rise  to  the  production  of 
two  new  bodies  ;  namely,  a  nitrogenous  alkaline  substance  and  plxx- 
phoglyceric  acid. 

As  to  the  physiological  character  or  significance  of  lecithine  we  are 
entirely  in  the  dark,  except  in  one  respect.  It  is  the  only  organic 
combination  in  the  body  containing  phosphorus.  Considering  the 
many  articles  of  food  in  which  it  is  an  ingredient,  it  must  be  intro- 
duced, in  no  small  quantity,  with  the  nutriment ;  and  it  certainly  exists 
abundantly  in  the  substance  of  the  nerves  and  nervous  centres.  But  as 
no  known  organic  combination  of  phosphorus  is  discharged  with  the 
excretions,  this  substance  must  pass  out  of  the  body  as  part  of  the 
phosphates  in  the  urine  and  the  perspiration.  On  this  account,  together 
with  the  fact  of  the  constant  consumption  of  oxygen  by  the  animal 
body,  it  is  believed  that  the  phosphorus,  introduced  as  an  ingredient  of 
organic  materials,  is  converted  in  the  system  into  phosphoric  acid,  and 
appears  finally  under  the  form  of  phosphatic  salts. 

2.  Cerebrine,  C17H33NO3. 

As  its  name  indicates,  this  is  an  ingredient  of  the  brain  and  nerves, 
the  only  parts  of  the  body  in  which  it  is  known  to  exist.  Although  not 
yet  obtained  in  a  crystalline  form,  it  is  placed  among  the  members  of 
this  group  because  it  resembles  them  in  its  general  features  of  chemical 
composition,  particularly  in  its  small  proportion  of  nitrogen,  and  also 
in  certain  reactions,  which  are  entirely  dissimilar  to  those  of  an  albu- 
minous matter. 

Cerebrine  is  insoluble  in  water,  but  if  treated  with  boiling  water  it 
swells,  softens,  and  yields  an  emulsion.  It  is  insoluble  in  cold  alcohol 
and  ether,  but  soluble  in  boiling  alcohol  and  ether,  from  which  it  is 
an  a  in  deposited  on  cooling.  Boiling  with  baryta- water  decomposes  it 
slowly  and  incompletely,  and  does  not  produce  phosphogly eerie  acid, 
as  cerebrine  contains  no  phosphorus.  If  strongly  heated  in  the  air,  it 
turns  brown,  melts,  and  finally  burns  with  a  bright  flame. 

It  is  much  more  abundant  in  the  white  than  in  the  gray  substance 
of  the  brain,  forming,  according  to  Petrowsky,  in  the  solid  ingredients 
of  the  white  substance  9.5  per  cent.,  in  those  of  the  gray  substance 
but  little  more  than  0.5  per  cent.  It  is  undoubtedly  a  constituent  of 
the  medullary  layer  of  nerve  fibres,  but  nothing  is  known  of  its  origin. 
metamorphoses,  or  physiological  activity. 


*: 
I 


CRYSTALLIZABLE    NITROGENOUS    MATTERS.  107 

3.  Leucine,  C6H13NO2. 

So  called  from  the  glistening  snow-white  color  of  its  crystals,  which 
are  in  the  form  either  of  thin  scaly  plates  or  of  radiating  needles.  It 
is  soluble  in  water,  less  so  in  alcohol,  and  insoluble  in  ether.  Heated 
slowly  to  lfO°  C.,  it  volatilizes  unchanged.  At  higher  temperatures 
it  is  decomposed,  giving  rise,  among  other  products,  to  carbonic  acid 
and  water.  Leucine  has  been  extracted  from  the  pancreas  and  the 
pancreatic  juice,  the  spleen,  thymus,  thyroid,  lymphatic,  parotid,  and 
submaxillary  glands,  the  liver,  kidneys,  and  supra-renal  capsules.  The 

ncreas  and  pancreatic  juice  are  the  only  situations  in  which  it  has 
n  found  in  abundance  ;  elsewhere  it  is  in  very  small  quantity,  though 
exact  proportions  have  not  been  determined.  It  does  not  occur  in 
the  blood  in  a  state  of  health,  and  has  been  found  in  the  urine  only  in 
certain  cases  of  disease. 

It  appears  as  one  of  the  results  of  the  artificial  decomposition  of 
albuminous  matters,  by  the  action  of  acids  or  alkalies,  and  also  in  the 
ordinary  putrefaction  of  these  substances.  It  is  often  found  among  the 
products  of  artificial  digestion  of  albumenoid  substances  by  the  trypsine 
ferment  of  the  pancreas  and  pancreatic  juice  ;  but  it  is  doubtful  whether 
any  importance  should  be  attributed  to  it  in  this  respect,  since  its 
quantity  in  the  intestine,  during  normal  digestion,  is  found  by  Schmidt- 
Mulheim*  to  be  quite  insignificant. 

Physiologists  generally  agree  in  considering  leucine,  in  the  living 
y,  as  derived  from  albumenoid  substances  in  the  act  of  retrogressive 

etamorphosis.  It  has  never  been  obtained  artificially  from  any  other 
source  than  albumenoid  matters ;  and  its  ready  production  from  these 
substances,  as  well  as  the  analogies  of  its  chemical  composition,  leave 
hardly  a  doubt  on  this  point.  But  as  it  does  not  appear  normally, 
either  in  the  blood  or  in  the  urine,  it  must  be  regarded  only  as  a  stage 
of  transition,  through  which  the  nitrogenous  matters  pass  before  being 
finally  converted  into  the  products  of  excretion. 

4.  Tyrosine,  CoHnNO3. 

This  substance  occurs  in  the  body  only  in  company  with  leucine, 
usually  in  much  smaller  quantity ;  and  it  also  appears  with  leucine  in 
the  products  of  artificial  decomposition,  digestion,  and  putrefaction  of 
albumenoid  matters.  It  was  so  named  from  having  been  early  found 
as  an  ingredient  in  old  cheese  (rvpos).  When  pure  it  is  in  the  form  of 
acicular  crystals,  nearty  insoluble  in  cold  water,  readily  soluble  in 
boiling  water,  insoluble  in  alcohol  and  ether.  It  is  regarded  as  simi- 
lar to  leucine  in  its  physiological  relations,  and  as  forming,  like  that 
substance,  an  intermediate  step  in  the  destructive  assimilation  of 
albumenoid  matters. 


4 

met 


*  Archiv  fiir  Anatomie  und  Physiologic.     Leipzig,  1879,  p.  39. 


108 


PHYSIOLOGICAL    CHEMISTRY. 


5.  Sodium  Glycocholate,  C26H42N06Na. 

This  and  the  following  substance  are  the  characteristic  ingredients 
of  the  bile.  Like  the  two  coloring  matters  of  this  secretion,  they  are 
mingled  in  various  proportions,  either  the  one  or  the  other  preponder- 
ating in  different  specimens,  or  in  the  bile  of  different  animals. 
Together  they  are  designated  as  the  "  biliary  salts." 

Sodium  glycocholate  is  a  saline  body,  consisting  of  a  nitrogenous 
organic  acid,  glycocholic  acid  (C26H43N06)  in  combination  with  sodium. 
Glycocholic  acid  is  so  called  because  by  boiling  with  potassium  hydrate 
or  baryta-water,  or  by  continued  boiling  with  dilute  hydrochloric  or 
sulphuric  acids,  it  is  decomposed  with  the  production  of  two  new 
bodies,  namely,  glycine  (C^H5N0.2),  a  nitrogenous  neutral  substance, 
and  cholic  acid  (C24H4005),  a  non-nitrogenous  organic  acid,  so  called 
because  peculiar  to  the  bile.  This  change  takes  place  with  the  assump- 
tion of  the  elements  of  water,  as  follows : 

Glycocholic  acid.  Glycine.          Cholic  acid. 

CV,H43X06  4-  H2O  ==  C2II5NO,  -f  C-JIvA. 

Sodium  glycocholate  is  a  neutral  crystallizable  substance,  very 
soluble  in  water  and  in  alcohol,  insoluble  in  ether.  It  is  extracted 
from  the  bile  as  follows :  The  bile  is  evaporated  to  dryness  over  the 
water-bath,  the  dry  residue  extracted  with  absolute  alcohol,  the 
alcoholic  solution  decolorized  with  animal  charcoal,  and  then  mixed 

with  from  8  to  10  times  its  vol- 

FJG.  16.  ume  Of  ether.     A  whitish  pre- 

cipitate is  thrown  down,  which 
collects  in  drops  and  masses,  of 
a  consistency  like  that  of  Canada 
balsam,  whence  the  biliary  salts 
are  sometimes  termed  the  "  res- 
inous "  matters  of  the  bile.  In 
the  course  of  24  hours,  some- 
times only  after  four  or  five 
days,  the  sodium  glycocholate 
crystallizes  in  hemispherical  or 
star-shaped  masses  of  fine  radi- 
ating needles.  The  crystals 
may  be  preserved  indefinitely 
in  the  mixture  of  alcohol  and 
ether;  but  if  the  liquid  be  poured 

SODIUM  GLYCOCHOLATK  FKOM   OX-ISILK,  afit-r  two     Og*    the    Cold    produced  by  CVap- 


days' crystallization.   At  th«-  Imv.-r  ,,art  ,,t 'th.-  ti- 

ure  the  crystals  are  melt  in  u' in  to  drops ,,  from  i-vup-     oration     CaUSCS     a    Condensation 

oration  of  the  ether  and  absorption  <>!  inmsturf. 

of  atmospheric  moisture  and  a 

rapid  solution  of  the  crystals,  which  liquefy  into  transparent,  rounded, 
oleaginous-looking  drops.  The  solubility  of  these  drops  in  water  and 
their  insolubility  in  ether  will  distinguish  them  from  oil  globules, 
which  they  closely  resemble  in  their  optical  properties.  Sodium  gly- 
cocholate may  bo  precipitated  from  its  watery  solution  by  both  the 


CRYSTALT.IZABT.E    NITROGENOUS    MATTERS.          109 

neutral  and  tribasic  lead  acetates.     Its  alcoholic  solution  rotates  the 
plane  of  polarization  toward  the  right  25.  f0. 

6.  Sodium  Tanrocholate,  C26H44NSO7Na. 

This  substance,  the  second  characteristic  ingredient  of  the  bile,  is 
similar  in  many  respects  to  the  foregoing.  Its  organic  acid,  tauro- 
cholic  acid  (C26H45NS07),  is  distinguished  by  containing  an  atom  of 
sulphur,  owing  perhaps  to  its  derivation  from  albuminous  matters. 
If  so,  glycocholic  acid  must  represent  a  product  of  further  alteration, 
in  which  sulphur,  hydrogen,  and  oxygen  are  given  up  in  such  pro- 
portions that  the  products  of  elimination  are  water  and  sulphur,  as 
follows  : 

Taurocholic  acid.  Glycocholic  acid. 

C26H45NSO7  —  ILO  —  S  =  C.,6H43N06. 

By  boiling  with  dilute  acids  or  alkalies,  or  even  with  water,  as  well 
as  under  the  influence  of  putrefaction,  taurocholic  acid  is  decomposed 
with  the  formation  of  two  other  bodies,  namely,  taurine  (C2H7NS03), 
a  neutral  nitrogenous  substance,  containing  the  sulphur,  so  called 
because  first  discovered  in  bullock's  bile,  and  cholic  acid  (C.24H4005), 
the  same  body  produced  by  a  similar  process  from  glycocholic  acid. 
The  change  takes  place  with  the  assumption  of  the  elements  of  water, 
as  follows : 

Taurocholic  acid.  Taurine.  Cholic  acid. 

C^H^NSO,  -f  H20  =  C2H7NS03  +  C,4H40O5. 

Sodium  taurocholate,  like  the  preceding  salt,  is  soluble  in  water 
and  in  alcohol,  and  insoluble  in  ether.  It  is  extracted  from  the  bile 
by  a  process  similar  to  that  already  described,  and,  after  precipita- 
tion by  ether,  crystallizes  in  slender  needles,  much  like  those  of  the 
glycocholate.  It  may  be  distinguished  from  the  last-named  substance 
by  its  reaction  with  the  salts  of  lead,  not  being  precipitated  from  its 
watery  solution  by  the  neutral,  but  only  by  the  tribasic  acetate.  If 
a  watery  solution,  therefore,  containing  both  biliary  salts  be  precipi- 
tated by  neutral  lead  acetate,  the  filtered  fluid  will  contain  the  tauro- 
cholate alone.  In  alcoholic  solution  it  rotates  the  plane  of  polarization 
toward  the  right  24.5°.  With  the  exception  of  glucose,  lactose  and 
glycogen,  the  biliary  salts  are  the  only  substances  known  in  the  animal 
body  which  exert  a  right-handed  rotation  on  polarized  light. 

The  proportion  in  quantity  of  the  two  biliary  salts  varies  somewhat 
in  different  cases.  Generally  the  glycocholate  may  be  said  to  prepon- 
derate in  the  bile  of  ruminant  animals,  taurocholate  in  that  of  the 
carnivora.  In  dog's  and  cat's  bile,  the  taurocholate  exists  alone.  In 
human  bile  both  substances  may  be  present,  sometimes  one  being  more 
abundant,  sometimes  the  other ;  according  to  some  writers  the  tauro- 
cholate existing  alone  or  in  larger  proportion  (Gorup-Besanez,  Hoppe- 
Seyler,  Robin,  Hardy),  according  to  others  the  glycocholate  (Bischoff, 
Lessen,  Ranke).  In  the  observations  of  Jacobsen,*  on  a  case  of  biliary 

*  Revue  des  Sciences  Medieales,  Paris,  1874,  vol.  iii.,  p.  85. 


110  PHYSIOLOGICAL     CHEMISTRY. 

fistula  in  man,  the  glycocholate  was  shown  to  be  a  constant  ingredient, 
while  the  taurocholate  was  either  absent  or  variable  in  quantity.     \V 
have  also  found  human  bile  to  contain  the  glycocholate  without  the 
taurocholate. 

The  biliary  salts  are  formed  in  the  tissue  of  the  liver,  and  are 
thence  discharged  with  the  bile.  They  are  derived,  in  the  opinion  of 
most  physiologists,  from  a  transformation  of  albuminous  matter 
indicated  by  the  nitrogen  and  sulphur  which  they  contain.  According 
to  the  observations  of  Ranke  on  a  patient  with  biliary  fistula,  the  aver- 
age quantity  of  the  organic  acids  of  the  bile  thus  produced,  in  a  man 
weighing  65  kilogrammes,  would  be  a  little  over  15  grammes  per  day. 
Although  a  small  amount  has  been  found  by  Hoppe-Seyler  in  the  feces, 
this  appears  to  be  much  less  than  the  total  quantity  produced  in  the 
liver  for  a  corresponding  time.  Similar  observations  on  animals  have 
also  shown  that  the  main  part  of  the  biliary  salts  are  not  discharged 
with  the  feces,  but  are  changed  in  the  intestine,  and,  probably,  reab- 
sorbed  under  another  form  by  the  blood. 

Pettenkofer's  Test  for  the  Biliary  Salts. — The  biliary  salts,  when 
in  considerable  quantity,  may  be  recognized  by  their  solubility  in 
water  and  in  absolute  alcohol,  their  insolubility  in  ether,  their  form 
of  crystallization,  and  their  reaction  with  the  salts  of  lead.  When 
present  in  small  proportion  they  are  detected  by  Pettenkofer's  test, 
which  consists  in  the  production  of  a  red  color,  changing  to  purple 
or  violet,  on  the  addition  of  cane  sugar  and  sulphuric  acid.  The  te>t 
is  applied  in  the  following  way  :  One  part  of  cane  sugar  is  dissolved 
in  four  parts  of  water.  Of  this  liquid,  one  drop  is  added  to  each  cubic 
centimetre  of  the  solution  of  biliary  salts.  On  treating  the  mixture 
with  a  few  drops  of  pure  sulphuric  acid,  the  biliary  acids  are  decom- 
posed, forming  cholic  acid.  If  the  biliary  salts  be  present  in  a  propor- 
tion of  not  more  than  one  part  in  500,  the  solution  remains  clear :  if 
in  larger  quantity,  the  cholic  acid  is  precipitated,  forming  a  whitish 
turbidity.  This  turbidity  is  again  cleared  up  on  the  continued  addition 
of  sulphuric  acid;  and  in  the  course  of  a  few  minutes  a  cherry-red 
color  appears,  changing  rapidly  to  a  violet,  and  subsequently,  if  the 
biliary  salts  be  present  in  the  proportion  of  one  part  in  500  or  over, 
to  a  deep  rich  purple.  In  very  dilute  solutions,  the  violet  or  purple 
color  may  not  be  distinctly  visible  before  the  end  of  an  hour. 

The  precautions  required  in  the  use  of  this  test  are  as  follows: 
First,  the  liquid  to  be  examined  should  be  free  from  other  organic  sub- 
stances, particularly  albuminous  and  coloring  matters.  For  this  purpose, 
it  should  be  evaporated  to  dryness,  the  dry  residue  extracted  with 
absolute  alcohol,  the  alcoholic  solution  decolorized,  if  necessary,  with 
animal  charcoal,  then  precipitated  with  ether  in  e.\ce-<.  and  the  ether 
precipitate  dissolved  in  water.  This  gives  a  i-lrar.  <•<>!. .rlrss  solution, 
free  from  organic  contamination.  Secondly,  as  the  solution  becomes 
heated  by  the  liberal  admixture  of  sulphuric  acid,  its  temperature 
.-hould  not  be  allowed  to  ri>e  above  70°  C.,  nor  to  full  much  below  this 


CRYSTALLIZABLE    NITROGENOUS    MATTERS.          Ill 

point.  For  that  purpose,  the  test-tube  may  be  cooled  by  occasionally 
immersing  it  in  cold  water.  Thirdly,  the  addition  of  sulphuric  acid 
should  be  made  slowly,  and  should  be  stopped  as  soon  as  a  red  tint 
begins  to  show  itself,  the  mixture  being  left  at  rest  until  the  violet 
and  purple  colors  are  developed. 

There  are  various  other  substances  which  yield  a  red,  violet,  or 
purple  color,  when  treated  with  sugar  and  sulphuric  acid.  Among 
these  are  oleine,  oleic  acid,  ethereal  oil,  amyl-alcohol,  albuminous 
matters,  and  the  salts  of  morphine  and  codeine.  Albumen  of  the 
blood,  white  of  egg,  and  the  opium  alkaloids  in  the  proportion  of  ten 
parts  per  thousand,  if  treated  with  Pettenkofer's  test,  all  produce  a 
color  undistinguishable  from  that  obtained  with  the  biliary  salts. 
These  substances,  however,  with  the  exception  of  morphine,  may  all 
be  excluded  by  previously  treating  the  fluid  as  above  described ;  namely, 
evaporating  to  dryness,  extracting  with  alcohol,  precipitating  with  ether, 
and  dissolving  the  precipitate  in  water.  The  salts  of  morphine  might 
still  remain,  as  they  are  soluble  both  in  water  and  in  alcohol,  and  may 
be  precipitated  by  ether  from  their  alcoholic  solution.  This  substance, 
however,  is  very  unlikely  to  be  present  in  an  extract  of  the  animal 
fluids,  especially  in  the  proportion  of  ten  parts  per  thousand. 

Pettenkofer's  test  is  a  very  delicate  one.  A  watery  solution  of  pure 
sodium  glycocholate,  made  in  the  proportion  of  one  part  to  2,000,  yields, 
at  the  end  of  fifteen  minutes,  a  clear  violet-pink  color,  if  the  test  be 
applied  with  care ;  and  a  solution  of  sodium  taurocholate,  in  the  pro- 
portion of  one  part  to  3,000,  will  give  a  similar  color  at  the  end  of  an 
hour.  The  characters  of  the  test  are  the  same  in  both  cases,  as  the 
reaction  is  really  produced  by  cholic  acid,  derived  from  the  decomposi- 
tion of  either  of  the  biliary  salts. 

The  spectrum  of  Pettenkofer's  test  may  be  of  service  in  distinguish- 
ing it  from  similar  reactions  produced  by  other  organic  substances.  If 
either  or  both  of  the  biliary  salts,  dissolved  in  water,  be  treated  with 
sugar  and  sulphuric  acid  until  a  violet  or  purple  color  is  produced,  and 
the  colored  fluid  then  placed  before  the  slit  of  the  spectroscope,  its 
spectrum  shows  a  wide  and  dark  absorption  band  at  E,  extending  from 
midway  between  D  and  E  to  a  quarter  part  the  distance  between  E 
and  F,  the  central  parts  of  the  band  being  darker  than  the  edges. 
Beyond  the  absorption  band,  the  spectrum  is  dim,  fading  gradually, 
and  terminating  somewhere  about  the  line  Gr. 

When  the  purple  color  produced  by  Pettenkofer's  test  with  the  biliary 
salts  is  very  pronounced,  the  fluid  is  usually  too  opaque  for  spectro- 
scopic  examination,  even  in  a  layer  of  one  centimetre ;  and  if  diluted 
with  water,  its  purple  color  disappears,  and  it  becomes  turbid,  owing 
to  re-precipitation  of  the  cholic  acid.  This  difficulty  may  be  obviated  by 
making  the  solution  of  biliary  salts  sufficiently  dilute  in  the  first  instance. 
A  solution  of  sodium  glycocholate,  in  the  proportion  of  one  part  to  500, 
treated  with  Pettenkofer's  test,  gives  in  a  few  moments  a  clear  violet- 
pink  color,  which  afterward  becomes  a  rich  purple.  The  purple  fluid 


112  PHYSIOLOGICAL    CHEMISTRY. 

is  so  opaque  that,  when  placed  before  the  slit  of  the  spectroscope  in  a 
layer  of  one  centimetre,  it  completely  extinguishes  everything  but  the 

Fio.  17. 


8P»  i  IU-.M  OK  PKTTKNKOFKK'S  TKST,  with  the  Biliary  Salts  in  watery  solution. 

red ;  and  yet  it  may  be  diluted  with  water  without  showing  any  turbidity 
or  losing  its  color.  A  solution  of  the  above  strength  is  amply  sufficient 
to  exhibit  Pettenkofer's  reaction  as  well  as  its  spectroscopic  characters. 
If  a  solution  of  the  biliary  salts  should  prove,  when  treated  by  Petten- 
kofer's test,  too  opaque  for  spectroscopic  examination,  another  portion 
may  be  reduced,  before  applying  the  test,  to  about  the  strength  of  one 
part  to  500.  When  a  strongly  colored  purple  fluid  has  been  rendered 
turbid  and  decolorized,  as  above  described,  by  the  addition  of  water,  its 
transparency  and  color  may  be  again  restored  by  the  addition  of  sul- 
phuric acid ;  but  this  method  is  less  convenient  than  the  former. 

If  Pettenkofer's  test  be  applied  to  the  biliary  salts  in  alcoholic  solu- 
tion, its  spectrum  contains  two  absorption  bands  instead  of  one.  The 
first  is  situated  at  E,  and  is  identical  with  that  in  a  watery  solution  of 
the  same  salts.  The  second  band,  at  F,  is  usually  rather  narrower  and 
fainter  than  the  first,  although  sometimes  the  two  are  of  equal  intensity. 

The  pink  or  purplish-red  fluid,  produced  by  Pettenkofer's  test  with  a 
watery  solution  of  either  codeine  or  morphine,  has  a  spectrum  some- 
what similar  to  that  of  the  biliary  salts.  If  the  ruddy  color  of  the  fluid 
be  strongly  pronounced,  its  spectrum,  even  in  a  layer  of  one  centime;  re, 
is  very  short,  terminating  about  midway  between  D  and  E,  or  even 
before  that  point,  showing  the  red  and  yellow  clear  and  bright,  but  very 
little  of  the  green.  If  diluted  with  water,  the  mixture  is  not  rendered 
turbid,  but  its  color  is  reduced,  being  soon  changed  to  a  faint  am  her,  or 
often  to  a  light  apple-green,  while  the  former  peculiarities  of  the  spec- 
trum disappear.  The  best  way  is  to  place  the  fluid  before  the  slit  of 
the  spectroscope  in  a  layer  of  two  centimetres  before  its  ruddy  line  is 
fully  developed,  and  while  it  is  still  of  a  light  pink.  The  color  then 
gradually  becomes  more  pronounced,  and,  when  it  has  attained  the 
proper  strength,  the  spectrum  exhibits  a  certain,  though  ill-defined 
absorption  band  jil  K.  Beyond  the  hand,  the  spectrum  is  very  dim, 
terminating  gradually  Let  ween  F  and  G. 

The  distinction  between  the  spectrum  of  Pettenkofer's  test  with 
biliary  salts  and  that  with  the  opium  alkaloids  is,  that  in  the  former 


CRYSTALLIZABLE    NITROGENOUS    MATTERS.          113 


case  the  absorption  band  at  E  is  very  distinct,  and  often  quite  black, 
when  viewed  in  a  layer  of  two  centimetres'  thickness  ;  while  in  the 


FIG.  18. 


SPECTRUM  OF  PETTENKOFER'S  TEST,  with  the  Biliary  Salts  in  alcoholic  solution. 

latter  it  is  always  dim  and  ill-defined.  With,  the  biliary  salts,  also,  the 
fluid  may  often  be  diluted  with  its  own  or  even  twice  its  volume  of 
water,  and  the  absorption  band  still  remain  visible ;  but  with  morphine 
or  codeine  a  very  moderate  dilution  destroys  the  character  of  the  spec- 
trum and  causes  the  absorption  band  to  disappear. 

The  violet-colored  fluid  produced  by  Pettenkofer's  test  with  albumen 
has  a  well-marked  and  peculiar  spectrum,  easily  distinguishable  from 
that  of  the  biliary  salts.  If  too  opaque  for  spectroscopic  examination, 
may  be  diluted  with  water  and  afterward  cleared  up  by  the  further 
dition  of  sulphuric  acid.  It  then  shows  a  single  absorption  band, 
extending  from  somewhere  about  the  line  E  to  the  line  F.  In  con- 

FIG.  19. 


- 


SPECTRUM  OF  PETTENKOFER'S  TEST,  with  albumen. 


ntrated  solutions  it  may  begin  considerably  to  the  left  of  E,  and 
extend  thence  to  F.  In  those  which  are  more  dilute,  it  may  reach 
only  from  a  little  beyond  E  to  F.  It  is,  therefore,  always  limited  on 
the  right  by  the  line  F,  extending  farther  toward  E  and  D,  according 
to  the  degree  of  concentration  of  the  liquid.  Its  edges  are  never  very 
well  defined,  but  are  more  distinct  when  the  band  is  narrow  than  when 
it  is  wide.  Beyond  the  band,  the  refrangible  portion  of  the  spectrum 
is  quite  dim. 

7.  Creatine,  C^HgNaO..,,  from  xpf'a*,  flesh. 

This  is  a  neutral  crystallizable  substance,  which  exists  in  the  mus- 

H 


114  PHYSIOLOGICAL     < '  H  K  M  I  ST  R  Y. 

cular  tissue,  both  voluntary  and  involuntary,  of  man  and  animals;  its 
proportion  in  human  muscles  being,  according  to  Neubauer,*  about 
two  parts  per  thousand.  It  has  also  been  found  in  minute  quantity  in 
the  blood,  the  brain,  and  the  kidneys.  It  is  soluble  in  cold,  very  readily 
in  hot  water,  slightly  soluble  in  alcohol,  insoluble  in  ether.  From  its 
watery  solution  it  crystallizes  in  transparent,  colorless,  rhombic  prisms 
of  firm  consistency.  It  is  decomposed  by  a  temperature  of  100  C, 
By  boiling  in  acid  solutions,  or  by  long-continued  boiling  in  water,  it 
is  transformed  into  another  closely  related  substance,  namely,  creati- 
nine.  If  boiled  with  baryta-water  it  produces,  among  other  substances. 
urea,  carbonic  acid,  and  ammonia.  Creatine  is  regarded  as  a  product 
of  the  metamorphosis  of  albuminous  matters,  especially  of  those  exist- 
ing in  muscular  tissue.  It  does  not  appear  in  the  urine,  but  under 
a  further  transformation,  probably  into  the  following  substance. 

8.  Creatinine,  C4H7N,0, 

Is  known  to  exist,  with  certainty,  only  in  the  urine.  Although  occa- 
sionally found  in  the  muscles,  it  is  generally  regarded  by  physiological 
chemists  (Neubauer,  Hoppe-Seyler,  Gorup-Bcsanez),  not  as  a  normal 
ingredient  of  the  muscular  tissue,  but  as  a  product  of  transformation 
of  the  previously  existing  creatine.  It  is  soluble  in  water  and  in 
alcohol,  but  only  slightly  soluble  in  ether.  It  crystallizes  in  colorless, 
glittering  prisms.  In  solution  it  has  a  strongly  alkaline  reaction, 
decomposes  the  combinations  of  ammonia,  and  forms  with  various 
acids  neutral  salts. 

The  chemical  relation  between  these  two  bodies  is  such  that  by 
hydration  or  dehydration  they  maybe  converted  into  each  other.  In 
the  interior  of  the  body  creatine  is  no  doubt  converted  into  creatinine, 
since  the  former  exists  normally  in  the  muscles,  while  the  latter  is  an 
ingredient  of  the  urine.  In  this  change  the  elements  of  water  are 
eliminated  as  follows: 

Great  i  m1.  Cre.-itinine. 

C4H9N3O2  —  H2O  =  C4H7N3O. 

Creatine  thus  represents  an  intermediate  stage  of  metamorphosis,  and 
finally  appears  in  the  urine  under  the  form  of  creatinine.  According 
to  Neubauer,  the  quantity  of  creatinine  discharged  by  a  healthy  man, 
under  ordinary  diet,  is  about  one  gramme  per  day. 

9.  Urea,  CH4N2O. 

This,  the  most  important  and  well  known  substance  of  its  class,  is 
the  principal  solid  ingredient  of  the  urine,  and  the  main  product  of  the 
decomposition  of  nitrogenous  matters  in  the  body.  It  is  most  abun- 
dant in  the  urine,  where  it  is  present  on  the  average,  in  man,  in  the 
proportion  of  26  parts  per  thousand;  while  in  the  blood  it  amounts  to 
onlv  0.1 1)  part  per  thousand.  As  it  makes  its  appearance  in  the  blood, 
it  is  drained  away  by  the  kidneys,  and  thus  accumulates  in  larger 


*NYnl,:ui«T  mid  V.^t-l.  Airily/.-  <!«••;  llarns.      Wii-sl>:i«h-n.  IsT'J.  p.  '20. 


CRYSTAT.LIZABLE    NITROGENOUS    MATTERS.          115 

proportion  in  the  urine.  This  is  shown  by  the  analyses  of  Picard, 
who  found,  in  the  dog,  the  proportion  of  urea  in  the  blood  of  the 
renal  arteries  0.36  per  thousand,  in  the  renal  veins  0.18  per  thousand. 

After  extirpation  of  the  kidneys,  in  the  dog,*  the  urea  in  the  blood 
of  the  general  circulation  increases  in  twenty-four  hours  from  2^  to 
nearly  8  times  its  former  proportion.  The  same  eifect  is  produced  by 
tying  the  renal  arteries,  or  by  ligature  of  both  ureters,  which  arrests 
the  functional  activity  of  the  kidneys.  Grehant  corroborated  the 
observations  of  Picard  in  regard  to  a  diminished  proportion  of  urea  in 
the  blood  of  the  renal  vein,  as  compared  with  that  of  the  renal  artery, 
in  the  healthy  animal  ;  but  after  ligature  of  the  ureter,  the  proportion 
of  urea  was  no  longer  diminished  while  passing  through  the  kidney. 
It  is  plain  from  these  experiments  that  the  immediate  source  of  urea 
is  not  in  the  kidneys,  but  in  some  other  part  or  parts  of  the  general 
system.  It  has  been  found  in  the  lymph,  the  aqueous  and  vitreous 
humors  of  the  eye,  the  crystalline  lens,  the  liver  and  the  spleen,  and  in 
minute  quantity  in  the  perspiration. 

Though  urea  is  evidently  derived  from  the  nitrogenous  organic  sub- 
stances, the  exact  manner  and  place  of  its  formation  in  the  body  have 
not  been  determined.  It  has  been  artificially  produced  by  Bechampf 
from  albuminous  matter,  placed  in  contact  with  potassium  permanganate 
in  watery  solution,  and  subjected  to  a  heat  of  60°  or  80°  C.  This  reac- 
tion has  been  confirmed  by  Ritter,J  in  whose  experiments  30  grammes 
albumen  furnished  0.09  gramme  of  urea,  and  the  same  quantity  of 

Tine,  0.0*7  gramme;  while  from  30  grammes  of  gluten,  in  an  average 

three  experiments,  there  was  obtained  0.2T  gramme  of  urea.     This 

ocess,  however,  is  not  one  of  simple  oxidation,  but  an  oxidation  with 
mposition,  in  which  various  other  substances  are  produced  at  the 

me  time. 

Urea  is  a  colorless,  neutral  substance,  very  soluble  in  water  and  in 
boiling  alcohol,  less  so  in  cold  alcohol,  nearly  insoluble  in  ether.  It 

ystallizes  in  four-sided  prisms,  which  are  decomposed  on  being  heated 
ve  120°  C.  Its  pure  watery  solution  may  be  kept  without  change 
ordinary  temperatures ;  but  by  continued  boiling,  or  by  a  short 
boiling  in  the  presence  of  alkalies,  it  is  decomposed  with  the  production 
of  ammonium  carbonate.  If  heated  with  water  in  an  hermetically  sealed 
tube  to  180°  C.  it  undergoes  the  same  alteration.  This  change  takes 

ce  with  the  assumption  of  the  elements  of  water,  as  follows : 

Urea.  Ammonium  carbonate. 

CH4N20  +  2ILO  =  (NHOiCO* 

Daily  quantity  of  Urea  and  its  variations. — The  quantity  of  urea 

*  Prevost  and  Dumas,  Annales  de  Chimie  et  de  Physique,  Paris,  1823,  tome  xxiii., 
90 ;  S£galas,  Journal  de  Physiologic,  tome  ii.,  p.  354 ;  Mitscherlich,  Tiedemann  and 
lelin,  Poggendorf's  Annalen,  band  xxxi.,  p.  303;  Cl.  Bernard,  Liquides  de 

FOrganisme.     Paris,  1859,  tome  ii.,  Deuxi6me  Le£on.    Grehant,  Centralblatt  fiirdie 

Medicinischen  Wissensehaften.     Berlin,  1870,  p.  249. 

f  Comptes  Rendus  do  ]'  Aondemie  dcs  Sciences.     Paris,  1870,  tome  Ixx.,  p.  866. 
;::  Comptcs  Rendus,  1871,  Ixxiii.,  p.  1219. 


116  PHYSIOLOGICAL     CHEMISTRY. 

excreted  by  a  healthy  man  is  about  35  grammes  per  day.  This  amount 
varies  with  the  size  of  the  body,  the  average  daily  proportion  of  urea 
to  the  weight  of  the  whole  body  being  0.5  per  thousand  parts.  Leh- 
mann,  in  experiments  on  his  own  person,  found  the  average  daily  quan- 
tity to  be  32.5  grammes.  Bischoff,  by  similar  experiments,  found  it  to 
be  35  grammes.  Hammond,  whose  weight  was  90  kilogrammes,  found 
it  to  be  43  grammes.  Draper,  whose  weight  \v;is  00  kilogrammes,  found 
it  20.5  grammes. 

It  has  been  shown  by  Draper,*  and  confirmed  by  other  obser\ 
that  there  is  a  diurnal  variation  in  the  normal  quantity  of  urea.  A 
smaller  quantity  is  produced  during  the  night  than  during  the  day ; 
and  this  difference  exists  even  in  patients  confined  to  the  bed  during 
the  whole  twenty-four  hours,  as  in  the  case  of  a  man  with  fracture  of 
the  leg.  Its  production  is  less  abundant  during  the  forenoon  than 
in  the  afternoon  or  evening,  the  maximum  occurring  from  3  to  5  hours 
after  the  principal  meal  of  the  day. 

An  important  variation  in  the  daily  excretion  of  urea  is  that  which 
corresponds  with  the  kind  and  quantity  of  the  food.  Urea  is  the  prin- 
cipal representative  of  the  decomposition  of  the  nitrogenous  ingredients 
of  the  body,  as  it  is  the  only  substance  containing  nitrogen  which  is 
discharged  in  any  considerable  amount  by  the  excretions.  A  compari- 
son of  the  nitrogen  contained  in  the  daily  food  with  that  discharged 
from  the  body  in  various  forms  shows  that  fully  85  per  cent,  reappears 
as  an  ingredient  of  the  urea;  the  remaining  15  per  cent,  being  con- 
tained in  the  uric  and  hippuric  acids  and  creatinine  of  the  urine,  and 
in  the  nitrogenous  matters  of  the  feces. 

All  observers  agree  that  the  quantity  of  urea  excreted  varies  in  pro- 
portion to  the  nitrogenous  matters  contained  in  the  food.  Lehman  nf 
found  in  experiments  on  his  own  person,  that  the  daily  amount  of 
urea  was  increased  by  animal  food,  diminished  by  vegetable  food,  and 
reduced  to  its  minimum  by  a  diet  consisting  exclusively  of  non-nitro- 
genous matters,  such  as  starch,  sugar,  and  fat.  The  comparative  re- 
sults were  as  follows : 

Kind  of  diet.  Daily  quantity  of  urea. 

Mixed 32.5  ^rami! 

Animal 53.2 

Vegetable 22.5 

Non-nitrogenous       ......        15.4 

It  also  appears,  from  the  observations  of  Mahomed,  J  that  the  influence 
of  a  change  of  diet  in  this  respect  is  manifested  very  rapidly  ;  twenty- 
four  hours  of  a  non-nitrogenous  diet  being  sufficient  to  reduce  the 
excretion  of  urea  50  per  cent.,  while  it  is  restored  to  its  ordinary  stand- 
ard within  three  or  four  hours  after  the  use  of  animal  food. 

Urea,   however,   does    not    depend    exclusively  on  the  direct    trans- 

*Nr\v  York  Journal  of  Mc.lirM.r,  Marrh,   L8 

f  Physiological  <  'hcmi-try,  Syclriiham  Kdition.      London,  is'i.'i.  vol.  ii.,  \>.  -l">0. 

Jl'avy,  I-'- M.I!  and  I  >irlrtics,  Philadelphia    Kdition,  1S7-1,  i>{>.  7'.»    81, 


CRYSTALLIZABLE     NITROGENOUS     MATTERS.         117 

formation  of  nitrogenous  matters  in  the  food,  but  is  also  derived  from 
the  metamorphosis  of  the  more  permanent  constituents  of  the  body ; 
since  it  continues  to  be  discharged,  though  in  diminished  quantity 
when  no  food  is  taken.  Lehmann  found  as  much  urea  in  the  urine 
after  twenty-four  hours  of  abstinence  from  all  food,  as  after  a  diet  of 
non-nitrogenous  matters.  In  the  dog,  when  subjected  to  entire  absti- 
nence, the  urea  is  reduced  in  three  or  four  days  nearly  to  one-third  its 
former  quantity,  but  is  still  present  in  about  the  same  proportion  at  the 
end  of  seven  days.  In  the  experiments  of  Parkes  on  a  man  subjected 
to  purely  non-nitrogenous  diet,  the  daily  excretion  of  urea  fell  on  the 
second  day  to  12  grammes,  but  afterward  remained  nearly  uniform,  at 
rather  more  than  half  that  quantity,  and  on  the  fifth  day  still  amounted 
to  T  grammes.  Urea  has  also  been  found  by  Lassaigne  in  the  urine  of 
man  after  continued  abstinence  from  food  for  fourteen  days. 

Yery  contradictory  statements  have  been  made  in  regard  to  the  influ- 
ence of  muscular  exertion  on  the  production  of  urea.  By  some  observers 
(Lehmann,  Flint,  Weigelin,  Parkes,  and  Yogel)  the  urea  has  been  found 
to  be  increased  during  or  after  unusual  bodily  activity  ;  by  others  (Fick 
and  Wislicenus,  Yoit,  Ranke)  it  has  been  denied  that  muscular  exertion 
causes  such  an  effect.  This  discrepancy  has  resulted  mainly  from  not 
taking  into  account  the  increase  or  diminution  of  nitrogenous  food 
simultaneously  with  the  periods  of  muscular  rest  or  activity.  There 
can  be  no  doubt,  since  the  observations  of  Flint*  on  the  pedestrian 
Weston,  afterward  repeated  by  Pavy,*j"  on  the  same  person,  with  essen- 
tially similar  results,  that  the  production  of  urea  in  man  is  considerably 
increased  by  muscular  exertion,  and  that  this  increase  is  over  and  above 
what  can  be  accounted  for  by  the  nitrogenous  food  consumed.  It  must, 
therefore,  be  attributed  to  the  functional  activity  of  the  muscular  system ; 
and  as  this  system  forms  no  less  than  40  per  cent.,  by  weight,  of  the 
entire  frame,  it  will  account  for  a  considerable  portion  of  the  urea  pro- 
duced. It  is,  also,  a  matter  of  common  experience,  both  for  man  and 
animals,  that  continued  and  laborious  muscular  activity  requires  a  cor- 
responding supply  of  nitrogenous  food ;  and  the  final  result  of  the 
internal  metamorphosis  of  such  substances  is  mainly  represented  by 
urea. 

10.  Sodium  TTrate,  C5H3N403Na. 

As  its  name  indicates,  this  is  a  saline  body,  consisting  of  a  nitro- 
genous organic  acid,  namely,  uric  acid  (C5H4N4O3),  in  union  with  so- 
dium. A  portion  is  also  in  combination  with  potassium,  but  the  sodium 
salt  is  in  much  the  greater  quantity.  The  urates  are  found  normally 
only  in  the  urine,  where  they  exist  in  the  proportion  of  about  1.45  parts 
per  thousand.  The  entire  quantity  of  uric  acid  excreted  by  a  healthy, 
full-grown  man,  is  about  O.T  gramme  per  day.  It  is,  therefore,  very 
much  less  abundant  than  urea ;  and,  according  to  the  researches  of  Ranke, 


*  New  York  Medical  Journal,  June,  1871. 
f  London  Cancet,  1876,  vol.  ii.,  p.  848. 


118  PHYSIOLOGICAL    CHEMISTRY 

the  proportion  between  the  two  is  very  constant,  their  relative  quan- 
tity in  the  same  individual  being  nearly  always — 

Uric  acid     .........  1  part . 

TTrea 45  parts. 

Uric  acid  is  a  colorless,  crystallizable  substance,  very  slightly  soluble 
in  cold  or  hot  water,  insoluble  in  alcohol  and  in  ether.  It  is  U-ss  easily 
decomposed  than  urea,  remaining  for  a  long  time  unchanged  under 
ordinary  conditions.  If  treated  with  concentrated  sulphuric  acid  it  is 
decomposed,  with  the  production  of  ammonia  and  carbonic  acid.  If 
boiled  with  dilute  nitric  acid,  it  dissolves  with  a  yellow  color  and 
abundant  liberation  of  gas-bubbles ;  and,  on  evaporation,  the  solution 
leaves  a  brilliant  red  stain,  which  is  changed  to  purple  by  the  addition 
of  ammonia  water.  This  is  known  as  the  "  murexide  test"  for  uric 
acid  or  the  urates. 

Uric  acid,  like  urea,  is  formed  within  the  body  by  the  metamorphosis 
of  nitrogenous  organic  substances.  It  is  most  abundant  under  the  use 
of  animal  food,  is  diminished  by  a  vegetable  diet,  and  is  reduced  to 
a  minimum,  though  it  does  not  entirely  disappear,  during  complete 
abstinence.  It  is  also  increased  by  muscular  exercise  and  diminished 
by  repose.  It  is  this  substance  which  indirectly  causes  the  acid  reaction 
of  the  urine.  It  is  nowhere  present  normally  in  a  free  form,  being  by 
itself  exceedingly  insoluble ;  but  simultaneously  with  its  production  it 
unites  with  part  of  the  alkaline  base  of  the  phosphates,  thus  becoming 
sodium  urate,  which  is  soluble  and  neutral  in  reaction,  and  giving 
rise  to  sodium  biphosphate,  which  communicates  to  the  urine  its  acid 
reaction. 

11.  Sodium  Hippurate,  C9H8NO:iNa. 

This  is  also  a  saline  body,  formed  by  the  union  of  sodium  with  a 
nitrogenous  organic  acid,  namely,  hippuric  acid  (C9H9N03),  so  called 
because  first  discovered  in  the  urine  of  the  horse.  It  is  comparatively 
abundant  in  most  herbivorous  animals,  especially  the  horse,  ox,  sheep, 
goat,  elephant,  camel,  and  rabbit ;  while  it  is  absent,  or  nearly  so,  in  the 
carnivorous  animals.  In  human  urine,  under  an  ordinary  mixed  diet, 
it  is  constantly  present,  amounting  to  about  0.35  gramme  per  day.  or 
about  one-half  the  quantity  of  uric  acid.  It  increa>e>  perceptibly  under 
a  vegetable  diet,  and  diminishes  or  disappears  under  the  exclusive  use 
of  animal  food.  It  thus  alternates  in  quantity,  under  these  circum- 
stances, with  uric  acid.  In  the  urine  of  the  horse,  which  normally 
contains  hippuric  acid,  alter  continued  abstinence  from  food,  this  sub- 
stance censes  to  appear  and  uric  acid  takes  its  place.  Herbivorous 
animals,  when  deprived  of  food,  are  placed  in  the  condition  of  carnivora, 
since  the  ingredients  of  the  urine  must  then  be  derived  from  the  meta- 
morphosis of  their  own  substance.  In  the  CM  If,  while  living  on  tin- 
milk  of  its  dam,  the  urine  contains  uric  acid;  after  the  animal  is 
weaned  and  begins  to  live  on  vegetable  food,  the  uric  acid  disappear.-. 
and  the  urine  contains  salts  of  hippuric  acid. 


CHAPTER  VII. 
FOOD. 

NDER  the  term  "  food  "  ar"e  included  all  substances,  solid  or  liquid, 
necessary  for  nutrition.     The  first  act  of  this  process  is  the  ap- 
>priation  from  without  of  the  materials  of  the  living  frame,  or  of 
)ther  substances  which  may  be  converted  into  them.     Like  the  tissues 
id  the  fluids,  therefore,  the  food  contains  various  ingredients,  both 
rganic  and  inorganic ;  and  the  first  important  fact  with  regard  to  them 
that  no  single  class  of  these  substances  is  sufficient  to  sustain  life, 
it  that  several  must  be  supplied  in  due  proportion,  to  maintain  the 
ly  in  a  healthy  condition. 

Inorganic  Ingredients  of  the  Food. 

Inorganic  substances,  although  they  afford  the  necessary  materials 
>r  vegetation,  are  not  sufficient  for  the  nourishment  of  animals,  which 
?pend  for  their  support  upon  elements  already  combined  in  the  organic 

rm.  The  inorganic  matters  are  nevertheless  essential  to  animal  life, 
id  require  to  be  supplied  in  sufficient  quantity  to  maintain  their  natural 

)portion  in  the  animal  solids  and  fluids.     As  they  are  generally  exempt 

>m  alteration  in  the  interior  of  the  body,  and  are  absorbed,  deposited, 
id  expelled  unchanged,  each  one,  as  a  rule,  requires  to  be  present  under 

own  form,  and  in  sufficient  quantity,  in  the  food.  This  is  especially 
•ue  of  water  and  sodium  chloride,  both  of  which  enter  and  leave 
le  system  in  abundant  daily  quantity ;  and  of  the  calcareous  salts 
rhich,  during  the  growth  and  ossification  of  the  skeleton,  are  largely 
^posited  in  the  osseous  tissue.  The  alkaline  carbonates,  phosphates, 
id  sulphates  are  partly  formed  within  the  system  during  the  meta- 
lorphosis  or  decomposition  of  organic  substances ;  but  their  elements 
lust  of  course  enter  the  body  in  some  form,  in  order  to  enable  these 
langes  to  be  accomplished. 

Since  water  enters  into  the  composition  of  every  part  of  the  body, 

is  an  important  ingredient  of  the  food.  In  man,  it  is  probably  the 
wst  important  substance  to  be  supplied  with  constancy  and  regularity, 
id  the  system  suffers  more  rapidly  when  deprived  of  fluids,  than 
'•hen  the  supply  of  solid  food  only  is  withdrawn.  Magendie  found, 
in  his  experiments  on  dogs  subjected  to  inanition,*  that  the  animals 
supplied  with  water  alone  lived  six,  eight,  or  even  ten  days  longer 

*  Comptes  Kendus  de  1' Academic  des  Sciences.     Paris,  tome  xiii.,  p.  256. 

119 


120  PHYSIOLOGICAL    CHEMISTRY. 

than  those  deprived  of  both  solids  and  liquids.  Sodium  chloride,  also, 
is  usually  added  to  the  food  in  considerable  quantity,  and  requires 
to  be  supplied  as  a  condiment  with  some  regularity  ;  while  the  remain- 
ing inorganic  materials,  such  as  calcareous  salts,  and  the  alkaline  phos- 
phates and  sulphates,  occur  naturally  in  sufficient  quantity  in  most 
articles  of  food. 

The  entire  quantity  of  mineral  substances  discharged  daily  by  a 
healthy  adult,  by  both  the  urine  and  perspiration,  averages  as  follows : 

QUANTITY  OF  MINERAL  MATTERS  DISCHARGED  PER  DAY. 
Sodium  and  potassium  chlorides       .         .         .         15.0  grammes. 
Calcareous  and  magnesian  phosphates'     .        .          1.0        " 
Sodium  and  potassium  phosphates    .         .         .          4.5         " 
Sodium  and  potassium  sulphates      ...          4.0        " 

24.5         " 

According  to  the  average  dietaries  for  adults,  in  full  health,  collected 
by  Play  fair,*  about  20  grammes  of  mineral  matter  are  daily  introduced 
with  the  food.  The  remainder  is  accounted  for  by  the  phosphates  and 
sulphates  formed  within  the  system  as  above  described. 

Non-Nitrogenous  Organic  Ingredients  of  the  Food. 

These  substances,  so  far  as  they  enter  into  the  composition  of  the 
food,  are  divided  into  two  natural  groups,  namely,  carbohydrates, 
including  starch  and  sugar,  and  fats,  including  all  varieties  of  ole- 
aginous matter.  Since  starch  is  converted  into  glucose  in  the  digestive 
process,  these  two  substances  may  be  regarded  as  having  the  same 
nutritive  value.  They  occur  abundantly  only  in  vegetable  products, 
and  the  herbivorous  ^ animals  alone  consume  them  in  considerable 
quantity  in  their  food;  while  the  carnivora  obtain  a  comparatively 
small  proportion  of  glycogen  and  glucose  in  the  tissues  and  juices 
upon  which  they  feed.  For  man  the  natural  diet  is  a  mixed  regimen 
of  animal  and  vegetable  food ;  and  it  is  invariably  found  that  a 
continued  privation  of  vegetable  substances  produces  a  craving  for 
carbohydrates,  which  indicates  their  necessity  for  healthy  nutrition. 

A  similar  question  has  arisen  with  regard  to  oleaginous  matters. 
Are  these  substances  indispensable  in  the  food,  or  may  they  be  replaced 
by  starch  or  sugar?  It  has  already  been  seen,  from  the  experiments 
of  Boussingault,  that  a  certain  amount  of  fat  is  produced  in  the  body 
over  and  above  that  taken  with  the  food;  and  it  appears  also  that 
a  regimen  abounding  in  saccharine  substances  is  favorable  to  the 
production  of  fat.  It  is  probable,  therefore,  that  the  materials  for  tin- 
production  of  fat  may  be  derived,  either  directly  or  indirectly,  from 
saccharine  matters.  But  saccharine  matters  alone  are  not  sullicieiit. 
Dumas  and  Milne- K<  1  \vardsf  found  that  bees,  fed  on  pure  sugar,  soon 
cease  to  work,  and  sometimes  perish  in  considerable  numbers;  but  if 


*  London  Chemical  Xi-\vs,  M:iy  12,  1st;.",. 

f  AntKilis  <le  <  'liiinic  rt  do  Physique,  .°nl  scric<,  toin.-   xiv.,  ]>.  400. 


FOOD.  121 

fed  with  honey,  which  contains  some  waxy  and  other  matters  beside 
sugar,  they  thrive  upon  it ;  and  produce,  in  a  given  time,  a  larger  quantity 
of  fat  than  was  contained  in  the  food. 

The  same  thing  was  established  by  Boussingault  with  regard  to 
starchy  matters.  He  found  that  in  fattening  pigs,  though  the  quantity 
of  fat  accumulated  by  the  animal  considerably  exceeded  that  contained 
in  the  food,  yet  fat  must  enter  to  some  extent  into  its  composition  to 
maintain  the  animal  in  good  condition ;  for  pigs,  fed  on  boiled  potatoes 
alone  (an  article  abounding  in  starch  but  nearly  destitute  of  oily  matter), 
fattened  slowly  and  with  difficulty ;  \vhile  those  fed  on  potatoes  mixed 
with  a  greasy  fluid  fattened  readily,  and  accumulated  much  more  fat 
was  contained  in  the  food.  In  order,  therefore,  that  an  animal 

ome  fattened,  it  must  be  supplied  not  only  with  the  materials  of  the 
,t  itself,  but  with  everything  else  necessary  to  maintain  the  body  in  a 
healthy  condition.  Oleaginous  matter  is  one  of  these  substances. 
We  cannot  assume  that  the  fats  taken  in  with  the  food  are  simply 
absorbed,  and  deposited  unchanged  in  the  system.  They  may  be  in 
great  measure  decomposed  or  transformed  in  the  process  of  nutrition ; 
those  which  appear  as  constituents  of  the  tissues  being  products  of 
new  formation,  derived  perhaps  from  a  variety  of  sources. 

It  is  certain  that  either  one  or  the  other  of  these  two  groups  of 
substances,  saccharine  or  oleaginous,  must  enter  into  the  composition 
of  the  food  ;  and  furthermore,  that,  though  oily  matter  may  sometimes 
be  produced  in  the  body  from  the  sugars,  it  is  also  necessary  that  it  be 

plied  under  its  own  form.     In  the  food  of  man  they  are  naturally 
iated  in  many  vegetable  alimentary  matters ;  while  the  fats  are 

plied  in  addition  from  a  variety  of  animal  substances. 

ut  neither  the  carbohydrates  nor  the  fats,  alone  or  associated  with 
each  other,  are  sufficient  for  nutrition.  Magendie  found  that  dogs,  fed 
exclusively  on  starch  or  sugar,  perished  after  a  short  time  with  symp- 
toms of  profound  disturbance  of  the  nutritive  functions.  An  exclusive 
diet  of  butter  or  lard  had  a  similar  effect.  The  animal  became  exceed- 
ingly debilitated,  though  without  much  emaciation  ;  and  after  death  the 
internal  organs  and  tissues  were  found  infiltrated  with  oil.  Boussin- 
gault* performed  a  similar  experiment,  with  like  result,  upon  a  duck, 
hich  was  kept  on  an  exclusive  regimen  of  90  to  100  grammes  of 

ter  per  day.  At  the  end  of  three  weeks  it  died  of  inanition,  although 
ery  part  of  the  body  was  saturated  with  oily  matter. 
Lehmann  was  led  to  the  same  result  by  experiments  upon  him- 
self, while  investigating  the  effect  produced  on  the  urine  by  different 
kinds  of  food.f  He  confined  himself  first  to  a  purely  animal  diet  for 
three  weeks,  afterward  to  a  purely  vegetable  diet  for  sixteen  days, 
without  marked  inconvenience.  He  then  put  himself  upon  a  regimen 
of  non-nitrogenous  substances,  starch,  sugar,  gum,  and  oil,  but  was  only 


s 

eve 


*  Chimie  Agricole.     Paris,  1854,  p.  1G6. 

f  Journal  fur  praktisehe  Chemie,  Band  xxvii.,  p.  257. 


122  1MI  YSIOMHJ-ICA  T,     ('II  KM  ISTRY. 

able  to  continue  this  diet  for  two,  or  at  most  for  three  days,  owing  to 
disturbance  of  the  general  health.  The  unpleasant  symptoms  disap- 
peared on  his  return  to  a  mixed  diet.  In  some  instances  a  restricted 
diet  of  this  kind  has  been  borne  for  a  longer  time.  Parkes*  kept  two 
soldiers  on  non-nitrogenous  food  for  five  consecutive  days  without  their 
exhibiting  serious  signs  of  physical  exhaustion.  Hammond,  f  in  experi- 
ments upon  himself,  lived  for  ten  days  on  a  diet  of  boiled  starch  and 
water.  After  the  third  day,  however,  the  general  health  began  to  dete- 
riorate, and  became  much  disturbed  before  the  termination  of  the  ex- 
periment; the  prominent  symptoms  being  debility,  headache,  pyrosis, 
and  palpitation.  After  the  starchy  diet  was  abandoned,  it  required  some 
days  to  restore  the  health  to  its  usual  condition. 

Nitrogenous  Ingredients  of  the  Food. 

The  nitrogenous  or  albumenoid  matters  enter  so  largely  into  the 
constitution  of  the  animal  tissues  and  fluids,  that  their  importance, 
as  elements  of  the  food,  is  easily  understood.  No  food  can  be  long  nu- 
tritious, unless  a  certain  proportion  of  these  substances  be  present. 
Owing  to  their  abundant  quantity  as  ingredients  of  the  body,  their 
absence  from  the  food  is  more  speedily  felt  than  that  of  any  other 
substance  except  water.  Albuminous  matters,  however,  when  taken 
alone,  are  no  more  capable  of  supporting  life  indefinitely  than  the 
rest.  It  was  found  in  the  experiments  of  the  French  "  Gelatine  Com- 
mission "|  that  animals  fed  on  pure  fibrine  and  albumen,  as  well  as  those 
fed  on  gelatine,  become,  after  a  short  time,  much  enfeebled,  refuse  the 
food  offered,  or  take  it  with  reluctance,  and  finally  die  of  inanition. 
This  result  has  been  explained  by  supposing  that  these  substances 
excite  after  a  time  such  disgust  that  they  are  either  no  longer  taken,  or 
if  taken  are  not  digested.  But  this  is  simply  an  indication  that  the 
substances  used  are  insufficient  and  finally  useless  as  articles  of  food, 
and  that  the  system  demands  other  materials  for  its  nourishment.  It 
is  well  described  by  Magendie,  in  the  report  of  the  commission  above 
alluded  to,  while  detailing  his  investigations  on  the  nutritive  qualities 
of  gelatine.  "  The  result,"  he  says,  "  of  these  first  trials  was  that  pure 
gelatine  was  not  to  the  taste  of  the  dogs  experimented  on.  Some  of 
them  suffered  the  pangs  of  hunger  with  the  gelatine  within  their  reach, 
and  would  not  touch  it;  others  tasted  it,  but  would  not  eat;  others 
still  devoured  a  certain  quantity  once  or  twice,  and  then  obstinately 
refused  to  make  any  further  use  of  it/' 

In  one  instance,  Magendie  succeeded  in  inducing  a  dog  to  take  a 
considerable  quantity  of  pure  fibrine  daily  throughout  the  whole  course 
of  the  experiment;  but  the  animal  nevertheless  became  emaciated,  and 
died  at  last  with  symptoms  of  inanition. 


*  Proceedings  Of  tin-  Koyal  Society  of   London,  March  lid, 
t  Experimental    Researches,    U-ini,r  tin-    I'ri/.c    Kssay  of  the    American    Medical 
Association  for  1857. 

j;  (  'om]>te>  Uendus  dc  1'  Academic.  de->  Sciences.      Paris,  1S41,  loin,  xiii.,  j.».  -G7. 


FOOT).  123 

It  is  evident,  therefore,  that  no  single  organic  substance,  nor  even 
any  one  class  alone,  is  sufficient  for  nutrition.  The  albuminous  mat- 
ters are  first  in  importance  because  they  constitute  the  largest  part 
of  the  mass  of  the  body ;  and  exhaustion  follows  more  rapidly  when 
they  are  withheld  than  when  the  animal  is  deprived  of  other  kinds  of 
alimentary  matter.  But  starchy  and  oleaginous  substances  are  also 
requisite  ;  and  the  body  feels  their  want  sooner  or  later,  though  plenti- 
fully supplied  with  albuminous  food.  Finally,  the  inorganic  saline 
matters,  in  smaller  quantity,  are  also  necessary  to  the  maintenance  of 
life.  In  order  that  the  animal  tissues  and  fluids  remain  healthy,  and 
perform  their  proper  functions,  they  must  be  supplied  with  all  the  in- 

ficnts  necessary  to  their  constitution ;  and  a  man  may  be  starved  to 
h  at  last  by  depriving  him  of  sodium  chloride  or  lime  phosphate  as 
ly,  though  not  so  rapidly,  as  if  he  were  deprived  of  albumen  or  oil. 
Composition  of  Different  Articles  of  Food. 
..;  the  most  valuable  and  nutritious  kinds  of  food,  adopted  by  the 
universal  and  instinctive  choice  of  man,  the  carbo-hydrates,  fats,  albu- 
minous and  inorganic  matters  are  all  usually  present  in  certain  pro- 
portions. 

Milk. — In  milk,  the  first  food  supplied  to  the  infant,  and  largely 
employed  in  various  culinary  operations,  all  the  important  groups  of 
nutritive  substances  are  represented.     It  is  a  white,  opaque  fluid,  con- 
ing, 1st,  of  a  serous  portion,  with  albuminous  matters,  sugar,  and 
neral  salts  in  solution,  and  2d,  of  fatty  globules  suspended  in  the 
watery  liquid.     It  is  this  mixture  of  oleaginous  particles  with  a  serous 
fluid  which  gives  to  the  milk  its  opacity  and  its  white  color.     Its  rich- 
ness in  fatty  matter  may  therefore  be  estimated  from  these  physical 
qualities.      The  ingredients  in  cow's  milk  are  present,  according  to 
yen,  in  the  following  proportions : 

COMPOSITION  OF  Cow's  MILK  IN  1,000  PARTS. 

Water 864 

Albuminous  matter 43 

Sugar  of  milk 52 

Fat 37 

Mineral  salts 4 

1~000 

Cow's  milk  resembles  human  milk  in  its  general  characters,  but  con- 
tins  a  larger  proportion  of  solid  ingredients,  especially  of  the  nitro- 
lous  and  saccharine  matters,  fat  being  present  in  nearly  the  same 
lount  in  each.     Sheep  and  goat's  milk  is  richer  in  both  nitrogenous 
and  fatty  matters ;  while  the  milk  of  the  ass  and  the  mare  contains  a 
greater  abundance  of  sugar,  but  is  comparatively  poor  in  nitrogenous 
matter  and  fat.     The  nitrogenous  matter  of  milk  consists  almost  entirely 
of  caseine,  associated  with  a  small  proportion  of  albumen.     Owing  to 
the  relative  quantity  of  these  two  substances,  milk  does  not  solidify  on 
boiling,   but   merely   covers   itself  with   u   thin  pellicle   of  coagulated 


11  U  t. 

min 


124  PHYSIOLOGICAL    CHEMISTRY. 

albumen,  the  caseine  remaining  liquid.  The  addition  of  any  acid,  how- 
ever, such  as  acetic  or  tartaric  acid,  will  precipitate  the  ca>eine  and 
curdle  the  milk.  If  milk  be  allowed  to  remain  exposed  to  the  air  at  a 
moderately  warm  temperature,  it  curdles  spontaneously,  owing  to  the 
development  of  lactic  acid,  from  transformation  of  its  sugar;  and  the 
>amc  change  will  occur  instantaneously  from  electric  disturbance,  during 
a  thunder-storm. 

The  caseine  of  milk,  artificially  coagulated  by  the  action  of  rennet, 
constitutes  cheese.  Rennet  is  the  dried  contents  and  mucous  membrane 
of  the  stomach  of  the  calf,  the  animal  being  killed  and  the  stomach 
taken  out  while  digestion  is  in  full  activity  and  the  gastric  fluids  abun- 
dantly secreted.  An  infusion  of  this  substance  even  in  small  quantity, 
added  to  fresh  milk  at  the  temperature  of  30°  C.  produces  coagulation 
in  fifteen  or  twenty  minutes.  The  coagulum  is  drained  from  the  watery 
serum  or  "  whey,"  and  afterward  pressed  into  the  form  of  cheese.  The 
variety  in  consistency  and  flavor  of  different  cheeses  depends  mainly 
on  the  proportion  of  fatty  matter  retained  in  the  coagulum,  and  on 
certain  slow  changes,  in  the  nature  of  fermentations,  which  go  on  in  it 
subsequently. 

The  fatty  matter  of  milk  is  suspended  in  its  serous  portion  under  the 
form  of  minute  spheroidal  masses.  These  masses  or  "  milk-globules  " 
are  not  quite  fluid  at  ordinary  temperatures,  but  have  a  semi-solid  con- 
sistency owing  to  their  containing  a  considerable  proportion  of  palmitine. 
The  fat  globules,  separated  by  churning  from  the  other  ingredients  of 
the  milk,  and  united  into  a  coherent  mass,  constitute  butter.  This  sub- 
stance, accordingly,  represents  the  oleaginous  ingredients  of  the  milk ; 
and  when  purified  from  the  watery  portions  entangled  with  it,  con 
mainly  of  palmitine  and  oleine,  with  certain  flavoring1  ingredients,  the 
principal  of  which  has  received  the  name  of  "butyrine."  These  sub- 
stances are  usually  mingled  in  the  following  proportions : 

Palmitine G8  parts. 

Oleine 30     " 

Butyrine  and  other  flavoring  matters         ...          2     " 

Too 

When  well  prepared  and  in  good  condition,  butter  constitutes  one  of 
the  most  valuable  and  easily  assimilated  forms  of  oleaginous  food.  If 
contaminated  with  the  nitrogenous  matter  of  the  milk,  its  fatty  ingre- 
dients after  a  time  become  decomposed  with  the  development  of  volatile 
fatty  acids;  in  which  condition  it  is  said  to  be  "rancid,"  and  is  no 
lunger  fit  for  food. 

Bread. — The  cereal  grains  resemble  each  other  more  or  less  in  their 
constitution,  all  of  them  containing  starch,  nitrogenous  matter,  dextrine 
or  sugar,  fat,  and  mineral  sails  in  various  proportions.  Wheat  is  dis- 
tinguished by  containing  a  larger  quantity  of  nitrogenous  matter  as 
compared  with  the  other  ingredients,  and  by  the  peculiarly  adhesive 
quality  of  this  substance,  which  has  received  accordingly  the  name  of 


FOOD. 


125 


"gluten."     The  different  grains  in  common  use  for  food  have,  when 
dry,  the  following  average  composition,  according  to  Payen. 

COMPOSITION  OF  THE  CEREAL  (TRAINS. 


Nitrogenous 
Matter. 

Starch. 

Dextrine, 
etc. 

Fat. 

Cellulose. 

Mineral 
Salts. 

Wheat       .... 

18.00 

66.80 

7.50 

2.10 

3.10 

2.50 

live       

12.50 

64.65 

14.90 

2.25 

3.10 

2.60 

Baric  v       .     .     „     . 

12.96 

66.43 

10.00 

2.76 

4.75 

3.10 

Oats     

14.39 

60.59 

9.25 

5.50 

7.06 

3.25 

Indian  corn  . 

12.50 

67.55 

4.00 

8.80 

5.90 

1.25 

Rice.      

7.55 

88.65 

1.00 

0.80 

1.10 

0  90 

Thus,  of  the  cereal  grains,  oats  contain,  next  to  wheat,  the  largest 
proportion  of  nitrogenous  matters  ;  but  they  also  contain  a  considerable 
abundance  of  cellulose,  or  indigestible  vegetable  tissue,  which  inter- 
feres with  their  nutritive  quality  as  human  food.  Indian  corn  is  espe- 
cially rich  in  fatty  ingredients,  while  rice  consists  mainly  of  starch,  and 
is  the  poorest  of  all  in  both  nitrogenous  and  fatty  ingredients. 

Wheat  is  more  valuable  than  the  other  cereal  grains  for  making 
bread,  not  only  on  account  of  its  larger  proportion  of  albuminous 
matter,  but  also  on  account  of  the  peculiar  glutinous  quality  of  this 
ingredient,  which  is  useful  in  giving  to  the  dough  a  proper  consistency, 
n  preparing  the  wheat,  the  grains  are  first  cleansed  from  husks  and 

herent  foreign  material,  ground  into  meal,  and  the  finer  and  whiter 
portions  from  the  interior  of  the  grain  separated,  by  sifting  and  bolting, 
from  the  coarser  external  parts,  or  bran.  Thus  purified,  the  flour 
consists  of  starch,  gluten,  diastase,  dextrine,  a  little  fat,  sometimes  a 
trace  of  sugar,  mineral  salts,  and  about  15  per  cent,  of  water,  which  is 
never  wholly  expelled  by  ordinary  drying.  For  making  into  bread,  the 
flour  is  mixed  with  about  one-half  its  weight  of  water,  and  kneaded 
into  a  flexible  dough  of  uniform  consistency.  The  next  process  is  the 
fermentation  of  the  dough.  For  this  purpose  a  little  yeast  is  incor- 
porated with  it,  and  the  mixture  allowed  to  remain  for  a  few  hours  at 
a  temperature  of  about  25°  C.  During  this  time  the  sugar  originally 
present  in  the  flour,  and  that  produced  from  the  starch  and  dextrine  by 
the  action  of  the  diastase,  passes  into  fermentation  under  the  influence 
of  the  yeast,  and  is  transformed  into  alcohol  and  carbonic  acid.  The 
alcohol  is  dissipated  by  evaporation ;  but  the  carbonic  acid,  generated 
in  small  gas-bubbles,  is  entangled  by  the  tenacious  gluten  of  the  flour, 
and  the  dough  is  thus  puffed  up  into  a  spongy,  reticulated  mass.  When 
the  fermentation  of  the  dough  is  completed,  it  is  placed  in  ovens,  and 
baked  at  a  temperature  of  210°  C.  The  effect  of  this  is  to  cook  the 
glutinous  part  of  the  dough,  communicating  to  it  an  agreeable  flavor, 
and  at  the  same  time  solidifying  it ;  so  that  the  baked  loaf,  when  cut 
open,  retains  its  spongy  texture.  It  is  thus  made  easy  of  mastication, 
and  readily  permeable  by  the  digestive  fluids.  The  spongy  texture 


126  PHYSIOLOGICAL    CHEMISTRY. 

acquired  by  bread  is  the  main  object  of  its  fermentation,  although  an 
agreeable  flavor  is  also  developed  by  the  process,  which  does  not  exist 
in  unfermented  bread.  The  interior  of  the  loaf,  in  baking,  does  not 
rise  above  100°  C.  ;  the  exterior,  which  is  subjected  to  a  higher  tem- 
perature, becomes  covered  with  a  crust  of  partially  torrefied  starch  or 
dextrine,  and  caramelized  sugar.  The  interior  of  the  loaf  also  usually 
retains  a  little  glucose,  not  destroyed  in  the  process  of  fermentation. 
A  considerable  portion  of  the  water  which  was  mixed  with  the  flour 
remains  united  with  its  organic  ingredients;  so  that  100  parts  of  flour 
will  usually  yield,  after  baking,  130  parts,  by  weight,  of  bread. 

Wheaten  bread  thus  prepared  has  the  following  average  composition  : 

COMPOSITION  OF  WIIEATEN  I>KKAI>. 

Starchy  matters  (stan-h.  dextrine,  glucose)        .          .          .  .">»;. 7 

Albuminous  mutter  (gluten,  etc.) 7.0 

Fatty  matter 1.3 

Mineral  matter  (calcareous,  magnesian,  and  alkaline  salts)  1.0 

Water •  .         .         .  U.n 

KID. <) 

Thus,  while  bread  contains  an  abundance  of  albuminous  and  starchy 
matter,  it  is  deficient  in  fat ;  and  instinct  leads  us  to  take  with  it  butter. 
fat  bacon,  or  some  other  form  of  oleaginous  food. 

The  good  quality  of  bread,  aside  from  that  of  the  flour  from  which 
it  is  made,  depends  mainly  on  the  process  of  fermentation.  If  this  be 
incomplete,  the  bread  is  heavy,  and  not  sufficiently  reticulated  in  texture. 
If  too  long  continued,  it  passes  into  an  acid  fermentation,  and  develops 
a  sour  taste.  When  properly  fermented,  the  bread  is  uniformly  light 
and  spongy,  and  has  no  acid  reaction. 

Meat. — The  muscular  flesh  of  various  animals  affords  the  most  valu- 
able and  nutritious  kinds  of  food,  among  which  beef,  mutton,  and  venison 
hold  the  highest  place.  The  muscular  fibre  itself  consists  almost  exclu- 
sively of  nitrogenous  matters,  but  in  point  of  fact  the  flesh  used  for 
food  is  always  accompanied  with  more  or  less  adipose  tissue,  and  even 
when  freed  from  visible  fat,  it  always  contains,  according  to  Payen 
and  Pavy,  more  or  less  oleaginous  matter  entangled  with  its  fibres.  In 
various  kinds  of  meat,  and  even  in  that  from  different  parts  of  the  same 
animal,  the  proportion  of  fat  will  vary  considerably ;  but  it  was  found 
by  Pavy,  in  one  of  the  best  and  most  commonly  used  portions  of  beef, 
to  amount  to  about  5  per  cent,  of  the  whole. 

COMPOSITION  OF  I>EKK  FI,KSH. 

Water ' 77.-') 

Allmminoiis  matter lfi.0 

Fat r,.o 

Mineral  salts _L5 

Toixb 

The  mineral   matters  consist  of  alkaline   chlorides   and  phosph; 
with  phosphate-  of  lime  and  magnesia. 


FOOD.  127 

In  cooking  meat  by  roasting  or  broiling,  the  external  parts  are 
exposed  to  a  rapid  heat  of  120°  or  130°  C.  by  which  their  albuminous 
ingredients  are  coagulated,  their  coloring  matter  turned  brown,  and  a 
characteristic  flavor  developed.  The  interior,  which  does  not  rise  above 
65°  C.  remains  red  and  juicy,  its  fluids  being  protected  from  evaporation 
by  the  coagulation  of  the  outer  portions.  In  boiling,  where  the  meat 
is  cooked  by  contact  with  the  boiling  water,  none  of  it  can  rise  higher 
than  100°  C.,  but  this  temperature  may  penetrate  through  the  whole 
of  its  substance,  producing  a  uniform  decolorization.  Notwithstanding 
the  coagulation  of  the  albuminous  liquids,  the  fibrous  connective  tissues 
are  gelatinized,  and  the  muscular  flesh  thus  partially  softened  and  dis- 
integrated. On  the  whole,  the  effect  of  cooking  upon  meat  is  to  increase 
the  consistency  of  its  albuminous  ingredients,  its  principal  benefit  being 
the  attractive  flavor  developed  by  heat,  and  an  increased  digestibility 
from  the  same  cause.  By  either  method,  meat  loses  in  cooking  from 
25  to  30  per  cent,  of  its  weight,  principally  by  the  escape  of  water  and 
liquefied  fat. 

Eggs. — The  eggs  of  various  animals  are  employed  for  food,  as  those 
of  the  common  fowl,  the  duck,  goose,  turkey,  sea-fowl,  turtles,  and  many 
fish.  Those  of  the  common  fowl  may  be  considered  as  representing  the 
general  qualities  of  this  kind  of  nutriment.  They  consist  of  the  globu- 
lar "yolk,"  surrounded  by  a  layer  of  albumen  or  "white."  The  com- 
position of  these  two  portions  is  nearly  the  same,  excepting  that  the 
yolk  contains  a  larger  proportion  of  solids,  and  particularly  of  fatty 
matter,  which  gives  to  it  its  yellow  color  and  rich  flavor.  A  compara- 
tive analysis  of  the  yolk  and  white  is  as  follows : 

COMPOSITION  OF  THE  FOWL'S  EGG. 

Yolk.  White. 

Albuminous  matter          .         .         .         .         16.0  20.4 

Fat 30.7 

Mineral  salts 1.3  1.6 

Water                                                                   52.0  78.0 


100.0  100.0 

The  mineral  matters  consist  mainly  of  sodium  and  potassium  chlorides, 
potassium  sulphate,  and  lime  and  magnesium  phosphates.  Of  the  entire 
contents  of  the  egg,  exclusive  of  shell,  the  yolk  constitutes  one-third 
and  the  white  two-thirds.  Cooking  produces  but  little  effect  upon  eggs 
except  to  coagulate  their  albuminous  matters,  developing  only  a  slight 
flavor  under  the  influence  of  heat. 

Vegetables.— Of  the  different  vegetables  used  as  food,  some  are 
valuable  for  their  starchy  and  albuminous  ingredients,  others  mainly 
for  their  saccharine  and  watery  juices.*  The  former  are  nutritious  in 
the  ordinary  sense  of  the  word,  though  much  less  so  than  bread  or 
animal  food ;  the  latter  are  useful  for  supplying  certain  materials  con- 
tained in  fresh  vegetable  juices,  which  are  essential  to  the  maintenance 
of  health.  The  most  important  of  the  first  group  are  represented  by 


128  PHYSIOLOGICAL    CHEMISTRY. 

the  potato  and  the  leguminous  seeds.    The  tuber  of  the  potato  abounds 
in  starch,  but  is  poor  in  other  nutritive  ingredients. 

COMPOSITION  OF  THE  POTATO. 

Starch 2<i.o 

Albuminous  mat-tor 2.5 

Sugar  and  1511111 1.1 

Fatty  matter 0.1 

Cellulose !.<> 

Mineral  and  vcirctablo  salts        ......  1.3 

Water 74.0 

ioo.o 

The  leguminous  seeds,  on  the  other  hand,  contain  an  abundance  of 
albuminous  matter,  similar  to  the  caseine  of  milk,  and  called  "  legumine." 

COMPOSITION'  OF  WIIITK  BKA.NS. 

Starch 55.7 

Albuminous  matter  ........  25.r> 

Fatty  matter 2.8 

Cellulose 2.9 

Mineral  salts 3.2 

Water '•>.!> 

100.0 

The  composition  of  dried  peas  is  very  similar  to  the  above,  the 
starchy  matters  being  present  in  rather  larger,  the  albuminous  in- 
gredients in  rather  smaller  proportion.  Notwithstanding  the  abun- 
dance of  nitrogenous  matter  in  leguminous  seeds,  its  quality  is  inferior 
to  that  contained  in  the  cereal  grains.  Peas  and  beans  also  have  a 
texture  which  renders  them  comparatively  difficult  of  digestion,  and 
requires  long  boiling  to  fit  them  for  use  as  food.  The  same  is  true  of 
many  juicy  and  saccharine  roots,  such  as  beets  and  parsnips,  which 
appear  to  have  a  comparatively  soft  consistency,  but  which  neverthe- 
less need  prolonged  boiling.  The  effect  of  cooking,  upon  vegetabL 
generally  to  disintegrate  and  soften  their  texture,  and  particularly,  by 
the  aid  of  heat  and  moisture,  to  bring  their  starchy  ingredients  into  a 
pasty  condition.  Raw  starch  is  nearly  or  quite  indigestible  by  man, 
and  if  taken  into  the  stomach  will  often  pass  unchanged  through  tin- 
bowels;  but  when  cooked  it  is  transformed  into  glucose  by  the  di 
tive  fluids,  it  is  for  this  reason  that  starchy  vegetables  require  more 
thorough  cooking  than  most  kinds  of  animal  food. 

Beside  the  more  solid  kinds  of  vegetable  food,  many  of  the  pulpy  and 
succulent  fruits  and  herbaceous  substances  are  valuable  as  an  addition 
to  the  nutritive  regimen — celery,  lettuce,  parsley,  spinach,  with  all  the 
sweet  fruits  and  melons,  being  used  with  advantage  either  in  the  raw 
or  cooked  form.  They  introduce  into  the  system  salts  of  the  vegetable 
acids,  such  as  malates.  tart  rates,  and  citrates,  the  privation  of  which 
for  a  long  time  is  one  of  the  inducing  causes  of  scurvy. 

It  is  evident,  therefore,  that    the   nutritive   value  of  any   article  of 


FOOD.  129 

food  does  not  depend  on  its  containing  either  one  of  the  alimentary 
substances  in  large  quantity,  but  upon  its  containing  them  mingled 
in  the  proportions  requisite  for  nutrition.  What  these  proportions  are 
cannot  be  determined  from  chemical  analysis,  nor  from  any  other  data 
than  those  of  observation  and  experiment. 

Requisite  Quantity  of  Food  and  of  its  Different  Ingredients. 

The  entire  quantity  of  food  required  per  day  varies  with  the  circum- 
stances of  the  individual,  such  as  the  size  and  weight  of  the  body,  the 
development  of  the  muscular  system,  the  temperature,  and  especially 
the  amount  of  physical  activity.  More  food  is  required,  on  the  aver- 
age, in  cold  than  in  warm  weather,  more  by  persons  of  a  muscular  than 
by  those  of  an  adipose  or  phlegmatic  constitution,  more  in  a  condition 
of  exertion  than  in  one  of  repose.  Even  the  proportion  of  different 
classes  of  proximate  principles  required  for  nutrition  varies  according 
to  special  conditions.  When  the  individual  is  perfectly  healthy,  and 
can  supply  himself  with  any  kind  of  nourishment  desired,  the  natural 
demands  of  the  appetite  afford  the  surest  criterion  for  both  the  quantity 
and  quality  of  food  to  be  used.  But  provision  must  often  be  made  for 
supplies  to  last  over  a  considerable  period,  as  in  military  or  exploring 
expeditions,  or  for  the  inmates  of  hospitals  or  asylums  where  the  diet 
must  be  regulated  to  a  great  extent  on  a  uniform  plan.  It,  therefore, 
becomes  important  to  know  both  the  quantity  and  kind  of  food  neces- 
sary for  the  support  of  life. 

The  standard  adopted  for  this  estimate  is  that  of  a  healthy  adult 
man,  employed  in  active  but  not  exhausting  occupation.  The  amount 
requisite  will  be  found  to  vary  in  either  direction  from  this  standard, 
according  to  the  circumstances  above  mentioned.  The  average  require- 
ments, as  given  by  different  authors,  do  not  vary  materially  from  each 
other  in  any  essential  particular.  According  to  our  own  observations, 
a  man  in  full  health,  taking  active  exercise  in  the  open  air,  and  restricted 
to  a  diet  of  bread,  fresh  meat,  and  butter,  with  water  and  coffee  for 
drink,  consumes  the  following  quantities  per  day : 

QUANTITY  OF  FOOD  REQUIRED  PER  DAY. 

Meat 453  grammes. 

Bread 540        " 

Butter  or  fat 100        " 

Water 1,530         " 

This  represents  the  daily  quantity  of  food  and  the  proportions  of  its 
?erent  kinds,  when  composed  of  such  materials  as  are  most  nutritious, 
d  of  the  most  uniform  composition.  For  the  continued  maintenance 
of  health  and  strength  in  a  working  condition,  other  articles,  such  as 
fresh  vegetables,  sugar,  milk,  fruit,  etc.,  should  be  mingled  with  the 
above,  in  a  variety  of  proportions ;  but  there  is  no  doubt  that  bread 
and  fresh  meat,  with  a  certain  quantity  of  fat,  will  prove  sufficient  for 
the  wants  of  the  system,  for  a  longer  time  than  any  other  articles  of 
food. 

I 


130  PHYSIOLOGICAL    CHEMISTRY. 

Such  a  diet  affords  the  best  means  of  ascertaining  the  absolute  and 
relative  quantities  of  the  different  ingredients  required  for  food.  If  we 
take  the  average  composition  of  meat  and  bread,  and  estimate  their 
albuminous,  starchy,  and  saline  matters,  together  with  the  water  con- 
tained in  both  solid  and  liquid  food,  we  find  that  the  daily  ration  is 
composed  nearly  as  follows  : 

Albuminous  matter    ......         130  grammes. 

Starch  and  sugar        ......         300         u 

Fat     .........         100 

Mineral  salts       .......  20         " 

Water         ........  2,000 

Of  the  mineral  salts,  nearly  eight  grammes  are  naturally  contained 
in  the  substances  used  for  food  and  drink  ;  the  remainder  consists  of 
sodium  chloride,  artificially  added  to  the  food,  or  used  in  its  preparation. 

The  proportion  in  which  the  albuminous  and  the  non-nitrogenous 
principles  should  be  mingled  in  the  food  is  of  considerable  importance, 
and  this  proportion  has  been  determined  within  very  accurate  limits. 
In  making  such  an  estimate  it  is  necessary  to  include  the  carbohydrates 
and  fats  under  the  same  head  ;  but  the  fats  are  properly  regarded  as 
having  a  different  alimentary  value  from  the  carbohydrates.  This  de- 
pends on  the  fact  that  the  final  result  of  the  transformation  in  the  liv- 
ing body  of  all  the  non-nitrogenous  substances  is  carbonic  acid  and 
water,  thus  representing  a  process  of  oxidation,  the  necessary  oxygen 
for  which  is  introduced  with  the  inspired  air.  But  the  capacity  for 
oxidation  of  the  fats  is  greater  than  that  of  the  carbohydrates,  as  shown 
by  the  relative  proportion  of  their  constituent  elements. 

The  composition,  by  weight,     (  ® 
of  starch  (C^A)  i.  j  *  J    or  ,„  100  parts.     H  JUT 

162  100.00 

Here  the  oxygen  is  already  present  in  sufficient  proportion  to  satu- 
rate all  the  hydrogen  by  the  formation  of  water  ;  while  the  44.47  parts 
of  carbon  will  unite  with  118.58  parts  of  oxygen  to  form  carbonic  acid. 

On  the  other  hand,  if  we  take  palmitine  as  representing  the  average 
constitution  of  the  fats,  we  have  — 

The  composition,  by  weight,     (£  61^ 

r**/nor  •<  H     98    or  in  100  parts.     H  12.15 

of  fat  (QuH.O.)  IB  Q  Q  n.92 


806  100.00 

Here  the  oxygen  is  present  in  much  diminished  proportion  ;  and,  tor 
complete  oxidation  of  the  fat,  to  form  carbonic  acid  and  water,  the  75.93 
parts  of  carbon  will  require  202.48  parts  of  oxygen,  and  the  12.15  parts 
of  hydrogen  will  need  85.28  additional,  over  and  above  the  11.92  parts 
of  oxygen  already  present.  Thus  the  quantities  of  oxygen  appropriated 
during  complete  oxidation,  by  starch  and  fat  respectively,  aru  as  fol- 
lows: 


FOOD.  131 

OXYGEN  REQUIRED  FOR  THE  COMPLETE  OXIDATION  OF 

100  parts  of  starch 118.58 

"         "        fat 287.76 

A  fatty  substance,  therefore,  has  a  capacity  for  the  production  of 
carbonic  acid  and  water,  by  oxidation,  about  2.4  times  greater  than 
that  of  starch.  In  estimating,  accordingly,  the  requisite  quantity  of 
all  the  non-nitrogenous  matters  taken  together,  the  fat  is  calculated  as 
starch ;  one  part  of  fat  being  reckoned  as  2.4  parts  of  starch.  This 
quantity,  added  to  that  of  the  carbohydrates  in  the  food,  is  called  the 
"  starch-equivalent  "  of  the  non-nitrogeiious  matters. 

But  if  we  compare  the  consumption  of  non-nitrogenous  substances, 
on  this  basis,  with  that  of  albuminous  matter,  the  latter  should  also  be 
reduced  to  its  "  starch-equivalent."  After  eliminating  from  albumen 
all  its  nitrogen  under  the  form  of  urea,  its  remaining  constituents  still 
have  a  higher  capacity  for  oxidation  than  a  corresponding  weight  of 
starch ;  the  exact  relations  of  the  two  being  as  follows : 

OXYGEN  REQUIRED  FOR  THE  COMPLETE  OXIDATION  OF 

100  parts  of  starch 118.58 

"         "       albumen 154.07 

Albumen,  consequently,  without  its  urea,  has  a  capacity  for  oxidation 
1.3  times  as  great  as  that  of  starch. 

RVhen  compared  in  this  way,  the  albuminous  matters  are  found  to 
stitute  22  per  cent.,  and  the  non-nitrogenous  matters  18  per  cent, 
the  entire  food ;  that  is,  the  quantity  of  non-nitrogenous  matter  is 
;hat  of  albuminous  matter  as  3.55  to  1. 

This  proportion  varies  to  some  extent  with  the  age  and  condition  of 
the  individual.  In  human  milk,  which  at  first  forms  the  exclusive  food 
of  the  infant,  according  to  the  average  analyses  of  Simon,  Yernois,  and 
Becquerel,  as  given  by  Milne  Edwards,  the  non-nitrogenous  matters  are 
to  the  albuminous  ingredients  as  2.27  to  1.  In  cow's  milk,  upon  which 
the  young  calf  is  sustained,  the  proportion  is  2.52  to  1 ;  while  in  hay 
and  green  grass,  the  food  of  the  adult  animal,  it  is  7.14  and  9.01  to  1. 
The  larger  proportion  of  albuminous  matter  in  the  food  at  an  early  age 
is  evidently  connected  with  the  growth  then  taking  place.  As  the 
albuminous  matters  constitute  the  larger  part  of  the  solid  ingredients 
of  the  body,  the  increase  in  weight  during  the  growing  period  demands 
a  corresponding  supply  of  these  substances  in  the  food. 

here  is  also  evidence  that  the  requisite  proportion  of  nitrogenous 
ter  varies  with  the  amount  of  physical  activity.  A  condition  of 
bare  subsistence  may  be  maintained  upon  a  diet  in  which  the  albumin- 
ous substances  are  in  smaller,  and  the  non-nitrogenous  matters  in  larger 
proportion ;  but  when  the  system  is  called  upon  for  a  greater  amount 
of  muscular  exertion,  the  proportion  of  albuminous  matters  must  be 
increased.  This  is  well  known  in  regard  to  horses  and  working-cattle 
generally.  In  a  state  of  comparative  inactivity  they  may  be  supported 


132  PHYSIOLOGICAL    CHEMISTRY. 

mainly  upon  grass  or  hay,  in  which  the  proportion  of  nitrogenous  to 
non-nitrogenous  matter  is  not  more  than  1  to  7.14  ;  but  when  employed 
in  active  labor  they  require  a  liberal  supply  of  oats,  in  which  the  pro- 
portion is  as  1  to  5.49.  In  Playfair's  diet  tables,  which  were  collected 
from  a  variety  of  sources,  including  those  of  prisons  and  infirmaries, 
those  of  the  American  and  European  armies  during  peace  and  in  active 
service,  and  of  certain  hard-working  laborers,  the  increase  of  albuminous 
matter,  with  increased  labor,  is  a  marked  feature.  While  in  a  bare 
subsistence  diet  the  proportion  of  albuminous  to  non-nitrogenous  matter 
is  as  1  to  4.52,  in  that  of  active  laborers  it  is  as  1  to  3.34.  The  follow- 
ing table  will  show  the  relative  increase  of  the  two  kinds  of  food  under 
different  conditions  of  exercise,  as  calculated  from  Playfair's  data. 

RELATIVE  INCREASE,  UNDER  DIFFERENT  CONDITIONS,  OF  ALBUMINOUS  AND  NON- 
NITROGENOUS  MATTERS  IN  THE  FOOD. 

Albuminous  Non- nitrogenous 

matter.  matter. 

Bare  subsistence  diet         ....        100  100 

Full  diet  with  moderate  exercise  180  147 

Diet  of  active  laborer        ....        232  155 

Diet  of  hard- worked  laborer  242  169 


Thus,  in  passing  from  a  bare  subsistence  diet  to  that  of  the  hard- 
worked  laborer,  the  non-nitrogenous  matter  of  the  food  is  less  than 
doubled,  while  the  albuminous  matter  is  considerably  more  than 
doubled. 

As  these  diet  tables  were  adopted  by  various  civil  and  military 
authorities  as  the  result  of  experience  in  the  practical  adaptation  of 
food  to  the  amount  of  work  performed,  they  may  be  regarded  as  ex- 
pressing with  great  approximation  to  certainty  the  physiological 
requirements  under  different  conditions.  They  are  corroborated  by 
the  variation  in  diet  adopted  in  the  convict  establishments  of  Great 
Britain,  as  given  by  Pavy.*  In  the  change  from  "  Light-labor  Diet" 
to  "  Hard-labor  Diet,"  while  the  non-nitrogenous  food  is  increased  only 
13.37  per  cent.,  the  albuminous  food  is  increased  16.15  per  cent. 

It  is  also  a  matter  of  interest  to  determine  the  quantity,  source,  and 
destination  of  the  different  chemical  elements  entering  into  the  compo- 
sition of  the  food.  Taking  the  average  composition  of  albuminous 
matters,  fat,  and  carbohydrates,  we  find  that  a  man  under  ordinary  full 
diet  takes  into  his  system  daily  the  constituents  of  the  food,  in  round 
numbers,  as  follows: 

DAILY  CONSUMPTION  IN  THE  FOOD. 


C 

H 

0 

N        8 

Albuminous  matter, 

130 

grammes,  containing     70 

10 

29 

20         1 

Starch 

300 

134 

18 

148 

Fat    . 

100 

76 

12 

12 

280 

40 

189 

*On  Food  and  Dietetics.     Philadelphia  edition,  1874,  p.  433. 


FOOD.  133 

Of  these  elementary  bodies,  carbon  and  nitrogen  are  considered 
especially  important ;  carbon  as  forming  the  most  abundant  and  char- 
acteristic ingredient  of  all  organic  combinations,  and  nitrogen  as  the 
distinguishing  element  of  albuminous  substances.  Of  these  two,  the 
system  requires  daily,  in  an  active  condition,  about  20  grammes  of 
nitrogen  and  about  280  grammes  of  carbon.  This  alone  makes  it 
evident  that  a  mixed  diet  of  animal  and  vegetable  food  is  the  most 
available  for  man.  Meat  contains,  according  to  Payen,  3  per  cent,  of 
nitrogen  and  11  per  cent,  of  carbon.  Consequently,  if  the  diet  were 
composed  exclusively  of  this  food,  the  necessary  quantity  of  nitrogen 
would  be  supplied  by  666  grammes  of  meat ;  but  in  order  to  obtain  the 
required  carbon,  2,545  grammes  would  need  to  be  consumed,  thus  in- 
volving a  waste  of  its  nitrogenous  matter.  On  the  other  hand,  bread, 
the  most  nutritious  of  vegetable  substances,  contains  1  per  cent,  of 
nitrogen  and  30  per  cent,  of  carbon.  Therefore,  if  this  were  the  only 
food  used,  933  grammes  would  be  sufficient  to  supply  all  the  carbon ; 
but,  in  order  to  obtain  the  due  amount  of  nitrogen,  it  would  be 
necessary  to  consume  2,000  grammes.  A  mixture,  accordingly,  of  the 
two  kinds  of  food,  in  which  nitrogenous  and  hydrocarbonaceous  matters 
respectively  preponderate,  is  best  adapted  to  supply  the  wants  of  the 
system  without  unnecessary  expenditure  of  material. 

The  changes  undergone  in  the  body  by  the  ingredients  of  the  food, 
and  their  final  destination,  vary  for  different  kinds.  The  carbohydrates 
no  doubt,  after  serving  their  purpose  in  the  animal  economy,  are 
finally  expelled  under  the  form  of  carbonic  acid  and  water.  The 
oxygen,  introduced  with  the  inspired  air,  produces  this  result  by  unit- 
ing with  the  carbon  of  the  organic  body,  while  its  hydrogen  and  oxygen, 
already  present  in  the  relative  quantities  to  produce  water,  are  liberated 
under  that  form.  This  result  is  expressed  by  the  following  formula : 


Starch.  Carbonic  acid.    Water. 

C6H1006  +  012  =  6(C02)  +  5(HfO). 


Thus  the  change  undergone  by  starch  and  allied  substances  in  the 
animal  body,  where  they  are  consumed,  is  precisely  the  reverse  of  that 
taking  place  in  the  act  of  vegetation,  by  which  they  are  produced. 

For  the  fats  the  change  is  a  similar  one,  their  only  final  prod- 
ucts, so  far  as  we  know,  being  carbonic  acid  and  water.  But  for 
this  they  require,  as  already  mentioned,  a  greater  supply  of  extra- 
neous oxygen,  since,  beside  their  larger  proportion  of  carbon,  they 
also  contain  hydrogen  which  requires  further  oxidation,  to  form  water. 
The  change  thus  undergone  by  fatty  substances  may  be  expressed  as 
follows : 

Fat.  Carbonic  acid.       Water. 

C61H9806  +  0146  =  61(00.)  +  49(H,0). 

In  the  case  of  albuminous  matters  the  process  is  a  different  one. 
These  substances  contain  an  element,  namely,  nitrogen,  which  does  not 
appear  in  the  carbonic  acid  and  watery  vapor  of  the  expired  breath, 


134  PHYSIOLOGICAL    CHEMISTRY. 

but  forms  a  distinguishing1  constituent  of  the  crystallizable  matters  of 
the  urine.  Of  these  matters,  urea  is  by  far  the  most  abundant,  and 
fully  five-sixths  of  the  nitrogen  taken  in  with  the  food  reappears  as  un 
ingredient  of  urea,  while  the  remainder  is  included  in  the  creatinine 
and  uric  and  hippuric  acids  of  the  urine,  and  in  the  excrementitious 
substance  of  the  feces. 

There  is  evidence,  however,  that  albuminous  matters  also  take 
part  in  the  formation  of  carbonic  acid ;  that  is,  although  all  their  nitro- 
gen is  discharged  under  the  form  of  urea  and  other  similar  combina- 
tions in  the  urine  and  feces,  all  their  carbon  does  not  appear  in  these 
excretions,  and  must  pass  out  by  some  other  channel.  While,  as  we 
have  seen,  130  grammes  of  albuminous  matter  are  taken  daily  with  the 
food,  containing  70  grammes  of  carbon,  only  35  grammes  of  urea  are 
discharged  during  the  same  time,  containing  7  grammes  of  carbon;  and, 
according  to  the  most  accurate  analyses,*  not  more  than  23  grammes 
are  discharged  daily  by  both  the  urine  and  feces  together.  This  leaves 
unaccounted  for  about  47  grammes  of  carbon,  or  two-thirds  of  the 
original  quantity,  which  must  pass  out  from  the  body  under  some  other 
form  of  combination.  The  same  thing  is  true,  to  a  considerable  extent, 
of  the  hydrogen  of  these  substances,  of  which  10  grammes  are  intro- 
duced daily  with  the  albuminous  matters  of  the  food,  while  not  more 
than  5  or  6  grammes  are  discharged  in  organic  combinations  with  the 
urine  and  feces.  The  albuminous  matters,  therefore,  not  only  give  rise 
to  the  elimination  of  urea,  but  also  contribute  to  the  production  of 
carbonic  acid  and  water. 

The  manner  in  which  this  takes  place  is  probably  by  the  separation 
of  some  of  the  elements  of  albumen,  in  the  form  of  urea,  while  the 
remainder  are  left  behind  as  a  non-nitrogenous  substance.  If  we  adopt, 
for  the  constitution  of  an  albuminous  body,  exclusive  of  its  sulphur, 
Lieberkiihn's  formula,  C72HmN18O22,  and  take  away  from  it  all  the  nitro- 
gen in  the  form  of  urea,  a  substance  will  remain  analogous  in  composi- 
tion to  a  fat,  thus — 

Albumen On        H112        N18        Oa 

9  Urea  (CH4NSO)  _C,         H^         Nia        O9 

Oes          H76  013 

The  remaining  substance  may  then  undergo  complete  oxidation 
without  the  further  production  of  a  nitrogenous  compound.  This 
double  result  of  the  decomposition  of  the  albuminous  substances,  to- 
gether with  the  fact  that  we  take  habitually  three  or  four  tim< 
much  non-nitrogenous  as  nitrogenous  matter  in  the  food,  will  explain 
the  preponderance  of  carbonic  acid  as  an  excretion  over  urea.  For 
while  the  average  daily  quantity  of  urea  is  only  35  grammes,  the 
carbonic  acid  exhaled  with  the  breath  amounts  to  from  700  to  800 
grammes;  the  quantity  of  carbonic  acid  produced  being,  by  weight, 
fully  twenty  times  as  great  as  that  of  the  urea.  Urea  is  a  nitrogenous 

*  Ranke,  Grundziige  der  Physiologic  des  Menschen.     Leipzig,  1872,  p.  298. 


FOOD. 


135 


substance  separated  by  decomposition  from  the  albuminous  ingredients 
of  the  system ;  while  carbonic  acid  represents  its  remaining  carbona- 
ceous elements  in  union  with  oxygen  introduced  by  the  breath. 

The  quantities  of  the  various  substances  taken  with  the  food  and 
discharged  with  the  excretions  are  liable  to  many  variations  from  the 
changing  condition  of  the  individual.  If  the  body  be  increasing  in 
weight,  the  substances  introduced  will  be  more  than  those  discharged ; 
if  it  be  diminishing,  the  material  discharged  will  be  more  than  that 
introduced.  Even  in  the  healthy  adult,  where  the  body  does  not 
msibly  gain  or  lose  for  long  intervals,  observation  has  shown  that 
icre  are  frequent  fluctuations  of  small  extent,  and  that  the  income  for 
single  day  rarely  counterbalances  exactly  the  outgo  for  the  same 
iriod.  Consequently  the  preceding  tables  cannot  be  taken  as  furnish- 
ig,  in  any  case,  a  uniform  and  invariable  standard,  but  only  as  showing 
what,  on  the  whole,  are  the  relative  quantities  of  the  ingredients  of 
the  food  and  the  bodily  frame.  Although  we  are  not  yet  able  to 
determine  all  the  changes  which  they  undergo  in  the  system,  there  is 
no  doubt  of  the  main  result  produced  by  their  transformation.  On  the 
one  hand,  we  have  certain  nutritious  substances  introduced,  and,  on  the 
other,  certain  excrementitious  products  discharged,  forming  a  double 
series,  which  may  be  expressed  as  follows : 


DISCHARGED  WITH  THE  EXCRETIONS. 
Urea. 

Carbonic  acid. 
Water. 


INTRODUCED  WITH  THE  FOOD. 
Albuminous  matter. 
Fat. 
Carbohydrates. 

This  represents  the  decomposition  and  metamorphosis  of  the  organic 
ibstances  proper ;  while  the  mineral  ingredients  of  the  food,  as  a  rule, 
through  the  system  unchanged. 


SECTION  II. 

FUNCTIONS  OF  NUTEITION. 


CHAPTER   I. 
DIGESTION. 

THE  first  act  in  the  process  of  nutrition  is  that  by  which  the  food  is 
liquefied  and  made  capable  of  absorption.  Animals  and  man  require 
for  their  sustenance  organic  materials ;  that  is,  substances  which  have 
already  formed  part  of  organized  bodies.  When  taken  as  food  these 
matters  are  almost  invariably  solid  or  semi-solid,  and  insoluble  in  water. 
The  alimentary  constituents  of  meat,  grain,  herbage,  and  vegetables  are 
mainly  solid  in  form ;  and  even  the  nutritious  substances,  naturally  fluid, 
such  as  milk,  white  of  egg,  and  other  albuminous  liquids,  are  usually 
more  or  less  solidified  by  cooking,  when  used  for  human  food.  These 
substances,  accordingly,  before  they  can  be  taken  up  by  the  blood- 
vessels, and  made  available  for  the  nourishment  of  the  tissues,  need  to 
be  reduced  to  a  soluble  condition.  The  preliminary  act,  by  which  this 
is  accomplished,  is  the  process  of  digestion. 

While  there  are  many  variations  of  detail  in  the  digestive  process, 
according  to  the  structure  and  habits  of  different  animals,  its  essential 
features  are  everywhere  the  same.  The  food  is  taken  into  a  canal, 
running  through  the  body  from  mouth  to  anus,  known  as  the  "  ali- 
mentary canal,"  exhibiting,  at  various  points,  enlargements,  con- 
strictions, or  diverticula,  and  receiving  the  secretions  of  various 
accessory  glands.  While  passing  through  this  canal  it  comes  in 
contact  with  certain  digestive  fluids,  secreted  by  the  mucous  membrane 
of  the  canal  and  by  the  accessory  glands, — which  act  upon  it  in  such  a 
way  as  to  liquefy  its  ingredients,  or  otherwise  modify  their  physical 
condition.  As  the  alimentary  mass  passes  from  above  downward, 
urged  by  the  muscular  action  of  the  intestine,  its  liquefied  parts  arc 
removed  by  absorption ;  while  the  remainder,  consisting  of  the  indi- 
gestible portions,  with  the  refuse  of  the  intestinal  secretions,  gradually 
acquires  the  consistency  of  feces,  and  is  finally  discharged  under  that 
form  from  the  intestine. 

The  alimentary  canal  varies  in  different  animals,  according  to  the 
comparative  development  of  its  different  parts.  In  herbivorous 
animals  generally,  it  is  longer  and  more  complicated  than  in  the 
carnivora.  In  man,  where  it  holds  an  intermediate  position  in  this 

136 


DIGESTION. 


137 


FIG.  20. 


respect,  it  is  about  six  times  the  length  of  the  body.  Its  principal 
divisions,  enumerated  from  above  downward,  are :  the  mouth,  the 
pharynx,  the  oesophagus,  the 
stomach,  the  small  intestine, 
and  the  large  intestine.  At 
its  commencement  (Fig.  20) 
is  the  cavity  of  the  mouth, 
which  communicates,  imme- 

ately    beyond    the    fauces, 

ith  the  pharynx.     From  the 

harynx,   a   straight    tubular 

nal,    the     oesophagus     (a), 
ds  directly  to  the  stomach 

),  a  flask-shaped  expansion, 

rrounded  at  its  cardiac  and 
pyloric  orifices  (c,  d)  by 
special  bands  of  muscular 
fibres.  Then  follows  the 
small  intestine  (e),  different 
parts  of  which,  owing  to  cer- 
tain differences  in  size,  struc- 
ture, or  convolution,  bear  the 
names  of  duodenum,  jejunum, 

d  ileum.     In  the  uppermost 
ivision,  or  duodenum,  are  the 
orifices  of  the  biliary  and  pan- 
creatic ducts  (f,  g).     Lastly, 
comes  the  large  intestine  (h, 

j,  k)  separated  from  the  pre- 
ing  by  the  ileo-ca3cal  valve, 

d  terminating  at  the  anus, 

here  it  is  provided  with  a 

ouble  sphincter  muscle  guard- 

g  its  orifice.  Everywhere 
he  alimentary  canal  is  com- 
posed of  a  mucous  membrane 
and  a  muscular  coat,  with  a 
layer  of  connective  tissue  be- 
tween the  two.  The  muscular 
coat  consists  of  a  double  layer 
of  longitudinal  and  transverse 

bres,  by  the  alternate  con- 
traction and  relaxation  of  which  the  food  is  carried  through  the  canal 
from  above  downward.  The  mucous  membrane  presents  a  different 
structure  in  different  parts.  That  of  the  mouth  and  oesophagus  is 
smooth,  with  a  hard,  white,  tessellated  epithelium,  which  terminates 
abruptly  at  the  cardiac  orifice  of  the  stomach.  The  mucous  membrane 


HUMAN  ALIMENTARY  CANAL.— a.  (Esophagus.  6. 
Stomach,  c.  Cardiac  orifice,  d.  Pylorus,  e.  Small 
intestine.  /.  Biliary  duct.  g.  Pancreatic  duct.  h.  As- 
cending colon,  i.  Transverse  colon,  j.  Descending 
colon,  k.  Rectum. 


138  FUNCTIONS    OF    NUTRITION. 

of  the  gastric  cavity  is  soft  and  glandular,  covered  with  transparent, 
columnar  epithelium,  and  thrown  into  minute  folds,  often  reticulated 
with  each  other.  In  the  small  intestine  it  presents  larger  transverse 
folds,  known  as  "  valvula3  conniventes,"  is  covered  with  villosities 
of  various  forms,  and  contains  throughout  an  abundance  of  tubular 
follicles.  Finally,  in  the  large  intestine  the  mucous  membrane  is 
smooth  and  shining,  free  from  villosities,  and  provided  with  a  gland- 
ular apparatus  different  from  that  of  the  preceding  parts. 

The  accessory  glandular  organs  of  the  digestive  apparatus  are  the 
salivary  glands  communicating  with  the  cavity  of  the  mouth,  and  the 
liver  and  the  pancreas  connected  with  the  duodenum. 

The  digestive  fluids,  derived  from  these  sources,  are  five  in  number; 
namely,  1st,  the  saliva  secreted  by  the  salivary  glands,  and  discharged 
into  the  mouth ;  2d,  the  gastric  juice,  supplied  by  the  mucous  mem- 
brane of  the  stomach ;  3d,  the  pancreatic  juice,  produced  by  the  pan- 
creas, and  conveyed  through  its  duct  into  the  duodenum ;  4th,  the  bile 
supplied  by  the  liver,  and  also  discharged  into  the  duodenum  ;  and, 
5th,  the  intestinal  juice  secreted  by  the  glandules  of  the  small  intestine. 
These  fluids  have,  in  general,  certain  well  marked  characters,  by  which 
they  are  readily  distinguished  from  each  other,  and  which  indicate  cor- 
responding differences  in  their  physiological  properties.  At  the  same 
time  each  one  is  a  compound  secretion,  containing  various  organic  in- 
gredients, the  product  of  different  physiological  acts.  Thus  the  throe 
pairs  of  salivary  glands  and  the  buccal  follicles  unite  their  secretions 
to  form  the  saliva  of  the  mouth;  the  gastric  juice  contains  an  organic 
ferment  and  a  free  acid,  both  essential  to  its  physiological  activity, 
and  produced  in  the  stomach  by  dissimilar  secretory  operations;  the 
pancreatic  juice  contains  no  less  than  three  different  albumenoid  mat- 
ters ;  and  the  bile  is  equally  complex  in  the  number  and  quality  of  its 
ingredients.  This  is  a  general  feature  of  the  secretions  belonging  to 
the  digestive  apparatus. 

It  is  the  aim  of  the  physiologist  to  ascertain  the  constitution  and 
properties  of  each  digestive  fluid,  and  to  learn,  if  possible,  its  action 
on  the  ingredients  of  the  food.  For  this  purpose,  the  method  of  ex- 
periment by  artificial  fistulae  has  been  largely  used,  and  with  very 
valuable  results.  By  inserting  a  silver  canula  into  the  parotid  or  sub- 
maxillary  duct,  in  various  animals,  the  secretion  of  either  gland  may 
be  obtained  without  admixture  from  other  sources.  A  fistula  of  the 
stomach,  established  through  the  abdominal  walls,  supplies  us  with 
gastric  juice,  and  similar  methods  have  been  adopted  with  the  gall- 
bladder and  the  pancreatic  duct.  By  this  means  the  time,  rapidity,  and 
quantity  of  each  secretion  is  ascertained,  as  well  as  its  variations  under 
external  or  internal  influences.  The  digestive  fluids  of  different  animals 
are  compared  with  each  other,  and  with  those  obtained  by  accidental 
fistuloe  in  man.  Lastly,  the  secretions  are  placed  in  contact  with 
different  alimentary  substances,  in  flasks  or  test  tubes,  at  the  tempera- 
ture of  the  body,  and  their  action  investigated  by  the  mode  of  artificial 


DIGESTION.  139 

digestion.  It  appears  from  these  experiments,  in  general  terms,  that 
each  digestive  fluid  has  not  only  an  action  of  its  own,  but  that  each 
one  of  its  ingredients  contributes  in  a  special  way  to  the  digestive 
process. 

Beside  the  use  of  artificial  fistulae  there  is  still  another  method  for 
the  experimental  study  of  the  digestive  fluids.  It  is  based  on  the  fact 
that  the  principal  organic  ingredient  of  a  secretion  is  in  most  instances 
produced  in  the  solid  substance  of  the  gland,  and  may  be  extracted 
y  proper  solvents  from  its  tissue.  To  the  solution  thus  obtained, 
needed  accessory  ingredients,  such  as  saline  matters,  or  dilute  acids 
alkalies,  are  added,  and  an  artificial  digestive  fluid  thus  produced, 
ilar  in  most  respects  to  the  natural  one.  It  is  then  subjected  to 
amination  in  regard  to  its  influence  on  alimentary  substances.  This 
ethod  has  received  a  wide  extension  of  late  years  with  the  use  of 
glycerine  as  a  convenient  menstruum  for  the  extraction  of  glandular 
products.  It  has  been  the  source  of  much  important  information,  but 
its  results  need  to  be  verified,  in  every  instance,  by  examination  of  the 
normal  secretion  in  the  living  animal. 

The  digestive  fluids  and  their  mode  of  action  are  especially  charac- 
terized by  the  presence  of  ferments.     In  every  instance  where  their 
digestive  function  is  plainly  evident,  its  dependence  on  the  activity  of 
a  ferment  is  equally  unmistakable.     In  experimental  digestions,  with 
either  the  normal  secretion,  or  artificial  extracts,  all  the  conditions  of 
oisture,  temperature,  degree  of  concentration,  and  the  like,  requisite 
r  the  operation  of  organic  ferments,  must  be  maintained ;  and  when 
ch  an  experiment  is  successfully  carried   out,  the  quantity  of  ali- 
entary  material  digested  is  far  greater  than  that  of   the  organic 
gredient  which  produces  the  effect. 

The  nature  of  the  change  caused  by  digestion  in  the  alimentary 
Jbstances  is  partly  physical  and  partly  chemical.  But  although  this 
ange  is  indispensable  for  the  absorption  of  these  substances  in  due 
antity,  it  does  not  consist  in  any  profound  alteration  of  their  chemi- 
characters.  The  alimentary  materials  are  not  decomposed,  nor 
nverted  into  substances  of  a  different  kind.  They  are  simply  trans- 
brmed  into  soluble  materials  of  the  same  class  with  themselves.  The 
carbohydrates  after  digestion  remain  carbohydrates,  the  albumenoid 
matters  are  still  albumenoids,  and  the  fatty  substances  retain  the  chem- 
cal  properties  of  the  fats.  The  transformation  of  starch  into  glucose 
the  digestive  process  is  an  act  of  hydration,  which  may  be 
accomplished  by  continued  boiling  with  water  and  a  mineral  acid 
outside  the  body.  Albuminous  matters,  in  digestion,  are  converted 
to  peptones.  This  change  is  also  regarded  as  a  hydration,  and  it 
further  been  shown  that  albumen  may  be  made  to  undergo  a  sim- 
ilar transformation  by  long  boiling  in  acidulated  water,  or  by  boiling 
at  a  high  temperature  under  pressure.  Thus  the  animal  ferments,  in 
the  alimentary  canal,  act  by  inducing  rapidly,  at  the  temperature  of 
the  body,  changes  which  would  otherwise  require  a  longer  time  or  more 


5 

ac( 
out 

has 


140  FUNCTIONS    OF    NUTKITION. 

powerful  agencies.  Lastly,  the  fatty  substances  are  reduced  to  a  state 
of  emulsion,  and  in  this  condition  diffused  through  the  digestive  fluids. 
This  effect,  which  is  mainly  due  to  the  contact  of  an  albuminous  liquid, 
may  be  aided  by  a  partial  acidification  and  saponification  ;  but  the  prin- 
cipal mass  of  the  fat,  in  undergoing  the  digestive  process,  only  assumes 
the  form  of  a  chylous  emulsion.  All  the  alimentary  substances  are 
accordingly  made  ready  for  absorption,  without  losing  the  essential 
features  of  their  chemical  constitution. 

In  the  following  pages  the  properties  of  the  digestive  fluids  will  be 
considered  in  detail,  together  with  the  action  exerted  upon  the  food  in 
different  parts  of  the  alimentary  canal. 

Mastication. 

The  process  of  mastication,  which  takes  place  in  the  mouth,  consists 
of  a  mechanical  trituration  of  the  food  by  the  teeth.  At  the  same  time 
it  is  mingled  with  the  saliva,  which  is  so  worked  into  the  alimentary 
mass  as  to  reduce  it  to  a  pasty  condition.  By  this  means  the  solid 
substances  of  the  food,  finely  divided  and  thoroughly  moistened,  are 
rendered  susceptible  to  the  action  of  the  digestive  fluids.  Food  swal- 
lowed either  in  large  masses  or  in  a  dry  condition  would  be  slowly 
affected  by  the  alimentary  secretions,  and  would  be  consequently  diffi- 
cult of  digestion ;  but,  when  comminuted  and  softened  by  mastication, 
it  presents  a  large  surface  of  contact  and  a  ready  permeability,  favor- 
able to  the  prompt  action  of  the  digestive  solvents. 

The  form  of  the  teeth  and  their  physical  action  vary  in  different 
animals  according  to  the  nature  of  their  food ;  being  adapted,  in  the 
carnivora,  mainly  for  wounding  and  lacerating ;  in  the  rodentia  for 
gnawing  and  cutting,  and  for  grinding  in  the  herbivora.  In  man  they 
are  adapted  for  a  mixed  diet  of  animal  and  vegetable  food,  and  com- 
bine a  general  resemblance  to  each  other,  with  certain  special  characters 
in  different  parts  of  the  mouth.  The  incisors,  four  in  number,  in  each 
jaw,  are  more  or  less  chisel-shaped,  with  a  cutting-edge  running  from 
side  to  side.  They  are  useful  in  separating  from  a  mass  of  food  the 
proper  quantity  to  be  taken  into  the  mouth.  The  canine  teeth,  one  on 
each  side,  in  each  jaw,  placed  immediately  behind  the  former,  are  some- 
what pointed  in  form,  and  are  immediately  followed  by  the  two  anterior 
molars,  which  are  thicker  and  stronger.  Finally,  the  three  posterior 
molars,  on  each  side  of  each  jaw,  complete  the  dental  arch  posteriorly. 
They  are  the  largest  and  strongest  of  the  set,  firmly  planted  in  the 
jaw,  and  present  upon  their  free  extremity  a  number  of  conical  and 
ridge-like  elevations,  separated  by  shallow  furrows.  They  are  espe- 
cially adapted,  by  their  form,  size,  and  situation,  for  the  comminution  of 
resisting  substances,  and  they  perform,  with  the  anterior  molars,  the 
main  part  of  the  work  of  mastication.  The  enamel  which  covers  the 
crowns  of  all  the  teeth,  and  which  is  the  hardest  substance  in  the  body, 
protects  their  substance  from  injury,  and  enables  them  to  exert  the 
necessary  physical  action  upon  the  food. 


DIGESTION. 


141 


FIG.  21. 


Notwithstanding  the  simple  character  of  the  masticatory  act,  it  is 
one  of  great  practical  importance.  If  hurriedly  or  imperfectly  per- 
formed, it  leaves  the  food  in  a  crude  and  intractable  condition,  liable  to 
cause  subsequent  disturbance  in  the  digestive  process.  It  is  a  necessary 
preliminary  for  the  more  complicated  physiological  changes  to  take 
place  in  the  remainder  of  the  alimentary  canal. 

Saliva. 

The  saliva  is  a  compound  fluid,  derived  from  the  secretion  of  four 
Ferent  glandular  organs — namely,  the  parotid,  submaxillary,  and  sub- 
igual  glands,  and  the  muciparous   glandules  of  the  mouth.      The 
mds  have  a  general  resemblance  to  each  other 
structure,  being  composed  of  distinct  irreg- 
trly  ovoidal   masses,  more   or   less  flattened 
ito  a  polygonal  form  by  mutual  compression, 
"hese   masses   or    lobules   are   connected   with 
corresponding   branches   of  the   salivary    duct, 
which  penetrate  into  their  interior,  and  there 
divide  into  smaller  tubes,  each  one  of  which  ter- 
minates in  a  rounded  sac  called  the  glandular 
follicle  or  alveolus.     The  appearance  presented 
ipon  an  injection  of  such  a  lobule  is  as  if  the 
)llicles  were  arranged  in  clusters,  like  grapes, 

-,  ,|_     -,   ,,  ,1       ,,     ,.  LOBULE  OF  PAROTID  GLAND 

ound  the  ends  01  the  smaller  salivary  tubes.     Of  newly-born  infant,  in- 

ig.  21.)     A  more  complete  examination  has 

own,  however,  that  the  follicles  are  simply 

e  rounded  extremities  of  tubular  or  sac-like  offshoots  from  the  sali- 
y  tube ;  and  that  it  is  the  windings  and  prolongations  of  the  tube 

hich  constitutes  the  secreting  follicles  of  the  gland.     The  follicles  are 

general  about  50  mmm.  in  diameter,  and  are  lined  with  glandular 
thelium  cells,  which  cover  their  internal  surface  and  nearly  fill  their 

vity ;  so  that  there  is  often  only  a  small  space,  toward  the  central 
part  of  the  follicle,  containing  a  transparent  fluid  produced  by  the 
secreting  action  of  the  cells.  The  cells,  which  are  arranged  in  a 
single  layer,  are  finely  granular  bodies,  about  15  mmm.  in  diameter, 
each  with  an  oval  nucleus,  situated  toward  the  external  part  of  the 
follicle.  They  are  closely  packed  together  in  various  polygonal  forms. 

The  salivary  tubes  or  ducts,  outside  the  follicles,  unite  into  larger 
nches,  until  they  reach  the  principal  excretory  duct.  They  are  lined 

ith  cells  which  differ  in  form  from  those  of  the  follicles,  being  elon- 
gated and  cylindrical,  each  with  a  nucleus  situated  about  its  middle 
portion.  It  is  probable  that  the  epithelium  of  the  salivary  ducts,  as 
well  as  that  of  the  follicles,  takes  part  in  the  process  of  secretion ; 
since  Pfliiger  has  found  that  in  sections  of  the  gland,  examined  immedi- 
ately after  being  taken  out  of  the  body,  drops  of  transparent  fluid 
may  be  seen  exuding  from  the  ends  of  the  cylindrical  epithelium 
cells  into  the  cavity  of  the  duct.  The  follicles  and  lobules  are  sur- 


jected  with  mercury.    (Wag- 
ner.) 


J 

wit 


142 


FUNCTIONS    OF    NUTRITION. 


rounded  with  a  delicate  layer  of  connective  tissue,  in  which  are  dis- 
tributed the  capillary  blood-vessels,  supplying  the  materials  for  secre- 
tion. 

FIG.  22. 


SECTION  OF  THE  SUBMAXILLARY  GLAND  FROM  THE  DOG.— a.  Salivary  duct,  with  cylindrical  epithe- 
lium aiid  central  cavity,    b.  Follicle,  with  glandular  epithelium  and  central  cavity.    (Kolliker.) 


FIG.  23. 


Physical  Properties  and  Composition  of  the  Saliva.  —  Human  saliva, 
from  the  cavity  of  the  mouth,  is  a  colorless,  slightly  viscid,  alkaline 
fluid,  with  a  specific  gravity  of  1.005.  When  first  discharged,  it  is 
frothy  and  opaline,  holding  in  suspension  minute  flocculi.  After  stand- 

ing for  some  hours  in  a  cylin- 
drical vessel,  an  opaque,  whitish 
deposit  collects  at  the  bottom, 
while  the  supernatant  fluid  be- 
comes clear.  This  deposit  (Fig. 
23),  consists  of  epithelium  scales 
from  the  internal  surface  of  the 
mouth,  detached  by  mechanical 
attrition,  minute,  roundish,  o-ran- 
ular,  nucleated  cells,  apparently 
epithelium  from  the  mucous  fol- 
licles, some  granular  matter,  and 
a  few  oil-globules.  The  super- 


natant fluid  has  a  faint  bluish 
tinge,  and  becomes  slightly  opa- 
lescent by  boiling  or  by  the  addi- 
tion  of  nitric  acid.  Alcohol  in 

excess  «"«•  the  precipitation 
of  abundant  whitish  flocculi. 
According  to  the  analyses  of  Bidder  and  Schmidt,  the  composition 
of  saliva  is  as  follows  : 


with  (Jran- 
'  *•"""•* 


DIGESTION.  143 

COMPOSITION  OF  THE  SALIVA. 

Water 995.16 

Albuminous  matter 1.34 

Potassium  Sulphocyanide 0.06 

Calcareous,  magnesian,  and  alkaline  phosphates  .         .  0.98 

Sodium  and  Potassium  chlorides  .....  0.84 

Mixture  of  epithelium 1.62 

1000.00 

Saliva,  accordingly,  is  one  of  the  least  concentrated  of  the  digestive 
secretions,  containing  but  a  small  quantity  of  organic  matter,  and  by 
no  means  a  large  proportion  of  mineral  salts ;  its  watery  ingredient 
being  by  far  the  most  abundant,  as  compared  with  the  other  animal 
fluids.  Its  albuminous  matter  consists  of  a  small  quantity  of  albumen, 
coagulable  by  Jieat  or  a  mineral  acid ;  more  or  less  mucine,  which  gives 
to  it  a  slightly  viscid  character,  and  is  coagulable  by  acetic  acid ;  and 
ptyaline,  a  substance  belonging  to  the  class  of  ferments,  which  is 
thrown  down  by  alcohol  in  excess.  Some  of  these  reagents,  accord- 
ingly, precipitate  all  the  albuminous  matters  present,  while  others  coag- 
ulate only  a  part  of  them.  The  sulphocyanide  may  be  detected  by 
adding  to  the  saliva  a  small  quantity  of  a  solution  of  iron  chloride, 
when  the  characteristic  red  color  of  iron  sulphocyanide  is  produced. 
A  similar  red  color  is  produced  by  the  action  of  the  ferric  salts  upon 
meconic  acid,  or  the  meconates  ;  but  the  two  may  be  distinguished 
from  each  other  by  the  fact  that  the  red  color  caused  by  the  presence 
of  a  sulphocyanide  is  destroyed  by  the  addition  of  either  gold  chloride 
or  mercurial  bichloride,  neither  of  which  affects  that  produced  by 
meconic  acid.  The  presence  of  a  sulphocyanide  in  human  saliva  is 
almost  constant,  and  we  have  never  failed  to  find  it  in  the  freshly 
collected  secretion.  Yierordt  has  calculated  its  amount  in  saliva  by 
measuring  the  absorption  of  light  in  the  green  and  blue  portions  of 
the  spectrum  of  the  red  fluid  produced  on  the  addition  of  iron  chloride ; 
and  has  found  it,  in  an  average  of  six  observations,  to  be  0.16  parts 
per  thousand. 

Saliva,  like  various  other  animal  fluids,  has  the  property  of  con- 
verting boiled  starch  into  glucose  at  the  temperature  of  38°  C.  Its 
action  is  not  strictly  confined  to  this  temperature,  but  will  go  on, 
though  with  diminished  rapidity,  both  above  and  below  it,  if  the  vari- 
ation be  not  too  great.  It  is  suspended,  however,  at  or  near  the 
freezing-point,  and  is  permanently  arrested  by  boiling  water.  It 
depends  on  the  presence  of  ptyaline,  the  special  ferment  of  the  saliva, 
which,  like  other  similar  bodies,  is  most  active  at  or  near  the  temper- 
ature of  the  living  body.  It  is  differently  affected,  however,  by  cold 
and  heat.  By  a  freezing  temperature  its  action  is  suspended  for  the 
time,  but  recommences  when  warmth  is  again  applied ;  while  boiling 
permanently  destroys  its  catalytic  property. 

The  secretions  produced  by  the  different  salivary  glands  vary  in  their 
physical  properties,  especially  in  the  degree  of  their  viscidity. 


144  FUNCTIONS    OF    NUTRITION. 

The  parotid  saliva  may  be  obtained,  from  the  human  subject,  in  a 
state  of  purity,  by  introducing  into  the  orifice  of  Steno's  duct,  through 
the  mouth,  a  silver  canula,  about  one  millimetre  in  diameter.  The 
other  extremity  of  the  canula  projects  between  the  lips,  and  the  saliva 
is  collected  from  its  orifice. 

The  result  of  many  observations,  conducted  in  this  manner,  is  that 
human  parotid  saliva  is  colorless,  watery,  and  alkaline  in  reaction.  It 
differs  from  the  mixed  saliva  of  the  mouth,  in  being  perfectly  clear, 
without  turbidity  or  opalescence.  Its  flow  is  scanty  while  the  jaws 
remain  at  rest ;  but  if  the  movements  of  mastication  are  excited  by 
the  introduction  of  food,  it  runs  in  much  greater  abundance.  We  have 
collected,  in  this  way,  from  the  parotid  ducts  of  one  side  only,  in  a 
healthy  man,  31.1  grammes  of  saliva  in  twenty  minutes;  and  in  seven 
successive  observations,  made  on  different  days,  comprising  in  all 
three  hours  and  nine  minutes,  we  have  collected  a  little  over  104 
grammes. 

Parotid  saliva  may  be  obtained  from  the  dog  by  exposing  Steno's 
duct  where  it  crosses  the  masseter  muscle,  and  introducing  into  it, 
through  an  artificial  opening,  a  silver  canula.  The  secretion  then  runs 
from  the  external  orifice  of  the  canula,  without  being  mixed  with  the 
other  salivary  fluids.  It  is  clear,  limpid,  and  watery,  and  without 
perceptible  viscidity,  resembling  in  these  respects  the  parotid  saliva  of 
man.  The  submaxillary  saliva  of  the  dog  is  obtained  in  a  similar 
manner,  by  inserting  a  canula  into  Wharton's  duct.  It  differs  from  the 
parotid  secretion,  as  regards  its  physical  properties,  chiefly  in  possessing 
a  well  marked  viscidity.  The  sublingual  saliva  is  also  colorless  and 
transparent,  and  is  more  viscid  than  that  from  the  submaxillary.  The 
secretion  of  the  muciparous  glandules  has  been  obtained  by  placing  a 
ligature  simultaneously  on  Wharton's  and  Steno's  ducts,  and  on  that 
of  the  sublingual  gland,  so  as  to  shut  out  from  the  mouth  all  their  secre- 
tions, and  then  collecting  the  fluid  supplied  by  the  mucous  membrane. 
This  fluid  is  very  scanty,  and  so  much  more  viscid  than  the  other  secre- 
tions that  it  adheres  strongly  to  the  surface  of  a  glass  vessel.  All  the 
salivary  secretions  of  the  dog  are  alkaline  in  reaction.  They  differ  from 
those  of  man  chiefly  in  the  absence  of  ptyaline,  and  in  their  consequent 
want  of  action  on  starchy  substances. 

Mode  of  Secretion  of  the  Saliva.  —  The  salivary  glands  differ 
from  each  other  in  the  abundance  of  their  secretion  and  in  the  intlu- 
ences  which  excite  their  activity.  The  parotid  saliva  is  most  abun- 
dantly poured  out  under  any  stimulus  which  excites  the  movement  of 
the  jaws,  such  as  the  mastication  of  dry  substances,  or  continuous 
speaking.  According  to  Bernard,  the  submaxillary  secretion  is  espe- 
cially increased  by  the  introduction  of  substances  which  excite  the 
taste ;  wnile  that  of  the  sublingual  glands  in  the  dog  is  exuded  at  the 
moment  of  deglutition,  and  aids,  with  that  of  the  muciparous  glandules, 
in  lubricating  the  mouth  and  fauces,  and  facilitating  the  passage  of  the 


DIGESTION.  145 

food.  Colin,*  in  experimenting  upon  the  horse  and  the  ox,  also  found 
the  parotid  saliva  excited  by  the  movements  of  mastication,  while  the 
submaxillary  secretion  was  increased  by  introducing-  into  the  mouth 
substances  having  a  marked  taste.  Both  the  parotid  and  submaxillary 
secretions  are  abundant  while  the  animal  is  feeding,  their  quantity 
being  proportional  to  the  rapidity  of  mastication  and  the  sapid  quality 
of  the  alimentary  substances.  They  are  both  either  suspended  or  much 
diminished  during  abstinence.  In  the  ruminants,  the  sublingual  saliva, 

e  the  submaxillary,  is  excited  by  sapid  substances  and  while  the 

imal  is  feeding.     Its  secretion  continues  during  abstinence,  contrib- 

ing  to  keep  the  surfaces  in  a  moist  condition. 

Another  indication  of  the  different  nervous  influences  by  which  the 

livary  glands  are  controlled,  is  that  in  the  ruminant  animals,  while 
ing,  both  the  parotid  and  submaxillary  glands  furnish  an  abundant 
supply  of  saliva ;  but  during  rumination,  although  the  parotid  glands 
are  in  full  secretion,  discharging  frequently  as  much  as  900  grammes 
in  fifteen  minutes,  the  submaxillary  glands  are  nearly  or  quite  inac- 
tive. Colin  has  also  found  that  in  the  ox,  horse,  and  ass,  the  parotid 
glands  of  the  two  opposite  sides,  during  mastication,  are  never  in 
active  secretion  at  the  same  time ;  but  that  they  alternate  with  each 
other,  one  remaining  quiescent  while  the  other  is  active.  In  these 
cases  mastication  is  said  to  be  unilateral;  that  is,  when  the  animal 
begins  feeding  or  ruminating,  the  food  is  triturated  for  fifteen  minutes 
more  by  the  molars  of  one  side  only.  It  is  then  changed  to  the 
itc  side,  where  mastication  is  performed  for  the  succeeding  fifteen 

inutes.  It  is  then  changed  back  again,  and  so  on  alternately ;  the 
ction  of  the  lateral  movements  of  the  jaw  being  frequently  reversed 
ing  the  course  of  a  meal.  By  establishing  a  salivary  fistula  simul- 

neously  on  each  side,  it  is  found  that  the  flow  of  saliva  corresponds 

ith  the  direction  of  the  masticatory  movement.  When  the  animal 
ticates  on  the  right  side,  it  is  the  right  parotid  which  secretes 

tively,  while  but  little  is  supplied  by  the  left ;  when  mastication  is  on 
left  side,  the  left  parotid  pours  out  an  abundance  of  fluid,  while  the 

ght  is  nearly  inactive. 

We  have  observed  a  similar  alternation  in  the  human  subject,  when 
tication  is  changed  from  side  to  side.  In  an  experiment  of  this 
kind,  the  canula  being  inserted  into  the  parotid  duct  of  the  left  side, 
the  quantity  of  saliva  discharged  during  twenty  minutes,  while  masti- 
cation was  performed  mainly  on  the  opposite  side  of  the  mouth,  was 
8.26  grammes ;  while  the  quantity  during  the  same  period,  mastication 
being  on  the  same  side  of  the  mouth,  was  24.25  grammes.  It  was 
therefore  nearly  three  times  as  much  in  the  latter  case  as  in  the  former. 

Daily  Quantity  of  the  Saliva. — Owing  to  variations  in  the  rapidity 
of  secretion  of  the  saliva,  and  also  to  the  fact  that  it  is  not  excited  in 
the  same  way  by  artificial  stimulus  as  by  the  presence  of  food,  it  is 


Physiologie  comparee  des  Animaux  Doruestiques.    Paris,  1854,  tome  i.,  p.  468. 

K 


146  FUNCTIONS    OF    NUTRITION. 

somewhat  difficult  to  ascertain  with  exactness  its  total  daily  quantity. 
The  first  attempts  to  do  so  were  made  upon  patients  affected  with  parotid 
fistula,  and  the  amounts  collected  were  so  small  as  to  lead  to  the  conclu- 
sion that  the  entire  quantity  of  saliva  was  not  more  than  ten  or  twelve 
ounces,  or  about  350  grammes  per  day.  Bidder  and  Schmidt,*  from 
more  extended  observation,  were  led  to  make  a  higher  estimate. 
One  of  these  observers,  in  experimenting  upon  himself,  collected  from 
the  mouth  in  one  hour,  without  artificial  stimulus,  97  grammes  of 
saliva  ;  and  he  calculates  the  amount  secreted  daily,  making  an  allow- 
ance of  seven  hours  for  sleep,  as  not  far  from  1620  grammes. 

On  repeating  this  experiment  we  have  not  been  able  to  collect  from 
the  mouth,  without  artificial  stimulus,  more  than  36  grammes  of  saliva 
per  hour.  This  quantity,  however,  may  be  greatly  increased  by  intro- 
ducing into  the  mouth  any  smooth  unirritating  substance,  such  as  glass 
beads  or  the  like  ;  and  during  the  mastication  of  food,  the  saliva  is 
poured  out  in  much  greater  abundance.  Even  the  sight  or  odor  of  nutri- 
tious food,  when  the  appetite  is  excited,  will  stimulate  to  a  remarkable 
degree  the  flow  of  saliva.  Any  estimate,  therefore,  of  its  total  quantity, 
based  on  the  amount  secreted  in  the  intervals  of  mastication,  would  be 
imperfect.  We  may  make  a  tolerably  accurate  calculation  by  ascer- 
taining how  much  is  really  secreted  during  a  meal,  over  and  above  that 
which  is  produced  at  other  times.  We  have  found,  by  experiments 
performed  for  this  purpose,  that  wheaten  bread  gains  during  complete 
mastication  55  per  cent,  of  its  weight  of  saliva  ;  and  that  fresh  cooked 
meat  gains,  under  the  same  circumstances,  48  per  cent,  of  its  weight. 
We  have  already  seen  that  the  daily  allowance  of  these  two  substances, 
for  a  man  in  full  health  and  activity,  is  about  540  grammes  of  broad 
and  450  grammes  of  meat.  The  quantity  of  saliva,  accordingly, 
employed  in  mastication  is,  for  the  bread  297  grammes,  and  for  the 
meat  216  grammes,  making  in  all  513  grammes.  According  to  the 
observations  of  Tuczek,f  which  were  made  in  a  similar  manner  on 
different  individuals,  the  average  daily  requirement  is  somewhat  less, 
namely,  469  grammes.  If  we  accept  the  mean  of  these  two  results, 
and  calculate  the  quantity  secreted  between  meals  as  continuing  for 
twenty-two  hours  at  the  rate  of  36  grammes  per  hour,  we  have  : 

Saliva  required  for  mastication  =     491  grammes. 

"      secreted  in  intervals  of  meals     =    792        " 

Total  quantity  per  day,  a  little  over        1280        " 

Physiological  Action  of  the  Saliva.  —  The  principal  function  of  t  he- 
saliva  is  undoubtedly  to  moisten  the  food  and  provide  in  this  way  for 
its  further  solution,  and  especially  to  assist  in  mastication,  by  which 
the  food  is  converted  into  a  pultaceous  mass.  This  is  mainly  accom- 
plished by  the  watery  ingredients  of  the  secretion,  while  the  albuminous 


*  Verdauungssaefte  und  Stoffwechsel.     Lrip/iij,  1S52,  ]>•  1. 
fZeitschrift  fur  Biologic.    Munchc-n,  1S715,  II:ind  xii.,  p.  534. 


DIGESTION.  147 

matters  aid  in  giving  to  the  masticated  food  the  requisite  consistency, 
and  also  serve  to  lubricate  its  surface  and  facilitate  deglutition.  This 
is  evident  from  the  fact  that  the  principal  trouble  resulting  from  defi- 
ciency of  the  saliva  is  a  difficulty  in  the  mechanical  processes  of  masti- 
cation and  swallowing.  Food  which  is  hard  and  dry,  like  crusts  or 
crackers,  cannot  be  masticated  and  swallowed  with  readiness,  unless 
properly  moistened.  If  the  saliva  be  excluded  from  the  mouth,  its  loss 
does  not  interfere  so  much  with  the  chemical  changes  of  the  food  in 
digestion,  as  with  its  physical  preparation.  This  is  the  result  of  exper- 
iments performed  by  various  observers.  Bidder  and  Schmidt,*  after 
tying  Steno's  duct,  together  with  the  common  duct  of  the  submaxillary 
and  sublingual  glands  on  both  sides  in  the  dog,  found  that  the  imme- 
diate effect  of  such  an  operation  was  "  a  remarkable  diminution  of  the 
fluids  exuding  upon  the  surfaces  of  the  mouth ;  so  that  these  surfaces 
retained  their  natural  moisture  only  so  long  as  the  mouth  was  closed, 
and  readily  became  dry  on  exposure  to  the  air.  Deglutition  was 
therefore  rendered  difficult  not  only  for  dry  food,  like  bread,  but  even 
for  that  of  a  tolerably  moist  consistency,  like  fresh  meat.  The  ani- 
mals also  became  very  thirsty,  and  were  constantly  ready  to  drink." 

Bernardf  also  found  that  the  only  marked  effect  of  cutting  off  the 
flow  of  saliva  was  a  difficulty  in  mastication  and  deglutition.  He  first 
administered  to  a  horse  500  grammes  of  oats,  and  found  that  this  quan- 
tity was  masticated  and  swallowed  in  nine  minutes.  An  opening  had 
been  previously  made  in  the  oesophagus  at  the  lower  part  of  the  neck, 
so  that  none  of  the  food  reached  the  stomach ;  each  mouthful,  as  it 
passed  down  the  oesophagus,  being  received  at  the  opening  and  exam- 
ined by  the  experimenter.  The  parotid  duct  on  each  side  of  the  face 
was  then  divided,  and  another  similar  quantity  of  oats  given  to  the 
animal.  Mastication  and  deglutition  were  at  once  retarded.  The 
alimentary  masses  passed  down  the  oesophagus  at  longer  intervals, 
and  their  interior  was  no  longer  moist  and  pasty,  but  dry  and  brittle. 
Finally,  at  the  end  of  twenty-five  minutes,  the  animal  had  succeeded 
in  masticating  and  swallowing  only  about  three-quarters  of  the  quan- 
tity which  he  had  previously  disposed  of  in  nine  minutes. 

It  appears,  furthermore,  from  the  experiments  of  Magendie,  Ber- 
nard, and  Lassaigne,  on  horses  and  cows,  that  the  quantity  of  saliva 
absorbed  by  food  during  mastication  is  in  direct  proportion  to  its 
hardness  and  dryness,  but  has  no  particular  relation  to  its  chemical 
qualities.  These  experiments  were  performed  as  follows  :(  The  oesoph- 
agus was  opened  at  the  lower  part  ofj  the  neck,  and  tied  between  the 
wound  and  the  stomach.  The  animal  was  then  supplied  with  a  pre- 
viously weighed  quantity  of  food,  and  this,  as  it  passed  out  by  the 
oesophageal  opening,  was  collected  and  again  weighed.  The  differ- 
ence in  its  weight,  before  and  after  swallowing,  indicated  the  quantity 

*  Verdauungssaefte  und  Stoffwechsel,  p.  3. 

fLeyons  de  Physiologie  Exp£rimentale.     Paris,  1856,  p.  146. 


148  FUNCTIONS    OP    NUTRITION. 

of  saliva  absorbed.     The  following  table  gives  the  results  of  some  of 
Lassaigne's  experiments  upon  a  horse : 

Kind  of  Food  employed.  Qiiantity  of  Saliva  absorbed. 

For  100  parts  of  hay 400  parts. 

"  barley  meal 186     " 

oats 113      " 

"  green  stalks  and  leaves          .        .          49     " 

It  is  evident  from  the  above  that  the  quantity  of  saliva  used  in 
mastication  has  not  so  much  to  do  with  the  chemical  character  of  the 
food  as  with  its  physical  condition.  When  the  food  is  dry  and  hard,  it 
requires  much  mastication  and  the  saliva  is  secreted  in  abundance ;  when 
it  is  soft  and  moist,  a  smaller  quantity  of  the  secretion  is  poured  out ; 
and  finally,  food  taken  in  a  fluid  form,  as  soup  or  milk,  or  reduced  to 
powder  and  moistened  with  a  large  quantity  of  water,  is  not  mixed  at 
all  with  saliva,  but  passes  at  once  into  the  stomach. 

The  action  of  human  saliva  which  converts  boiled  starch  into  sugar, 
would  seem  to  indicate  a  further  connection  with  the  digestive  process. 
This  action  will  sometimes  take  place  with  great  promptness  in  an  arti- 
ficial mixture  of  starch  and  saliva.  Traces  of  glucose  may  be  detected 
in  such  a  mixture  in  one  minute  after  the  two  substances  have  been 
brought  in  contact ;  and  starch  paste,  introduced  into  the  mouth,  if 
already  at  the  temperature  of  38°  C.,  will  yield  traces  of  sugar  at  the 
end  of  half  a  minute.  Its  rapidity,  nevertheless,  as  noticed  by  Leh- 
mann,  varies  much  at  different  times.  It  is  frequently  impossible,  even 
with  the  mixture  kept  steadily  at  the  temperature  of  38°  C.,  to  find 
evidence  of  sugar  under  five,  ten,  or  fifteen  minutes ;  a  difference  prob- 
ably dependent  on  the  varying  constitution  of  the  saliva. 

Notwithstanding,  furthermore,  the  occasional  rapidity  of  this  action, 
it  is  not,  on  the  whole,  a  very  efficient  one  in  regard  to  quantity ;  that 
is,  only  a  small  portion  of  the  starch  is  converted  into  glucose  within 
a  given  time,  the  greater  part  remaining  unchanged.  This  is  proved 
by  the  fact  that  such  a  mixture  will  exhibit  the  reaction  of  starch  with 
iodine  long  after  Fehling's  test  has  shown  the  existence  of  glucose.  If 
a  solution  of  boiled  starch,  in  the  proportion  of  3,parts  of  starch  to  100 
parts  of  water,  be  mixed  with  one-third  its  volume  of  fresh  human 
saliva,  and  placed  in  the  water-bath  at  the  temperature  of  38°  C.,  it 
will  often  give,  in  one  minute,  a  prompt  sugar-reaction  with  Fehlin-r's 
test  ;  but  it  also  contains,  at  the  same  time,  an  abundance  of  unaltered 
starch.  Even  at  the  end  of  an  hour,  according  to  our  own  observa- 
tions, the  starch  is  far  from  being  entirely  converted,  and  the  mixture 
will  still  give  a  strong  purple-blue  color  on  the  addition  of  iodine. 
The  same  persistence  of  starch  in  considerable  proportion  may  be  seen 
when  the  mixture  is  retained  in  the  mouth.  If  a  thin  paste  of  boiled 
starch,  containing  no  traces  of  sugar,  be  taken  into  the  mouth  and 
thoroughly  mixed  with  the  Imccal  secretions,  it  will  often,  as  above 
mentioned,  begin  to  show  the  reaction  of  glucose  in  half  a  minute; 


DIGESTION.  149 

but  some  of  the  starchy  matter  still  remains,  and  will  continue  to 
manifest  its  reaction  with  iodine  for  fifteen  or  twenty  minutes,  or  even 
for  half  an  hour. 

These  facts  have  an  evident  bearing  on  the  disputed  question 
whether  the  sugar-producing  property  of  human  saliva  be  an  essential 
part  of  its  physiological  action  ;  that  is,  whether  the  saliva,  in  fact, 
transforms  the  starch  of  the  food  into  glucose.  If  the  digestion  of  the 
food  took  place  in  the  mouth,  or  if  it  were  retained  there  for  any 
considerable  time,  there  would  be  no  doubt  in  this  respect.  But  in 
reality  the  passage  of  the  food  through  the  mouth  is  momentary,  and 
only  sufficient  for  mastication.  This  time  is  too  short  for  complete  con- 
version of  the  abundant  starchy  matter  in  bread  or  vegetables,  which 
must  be  swallowed  into  the  stomach  in  great  measure  still  unchanged. 
Some  observers  (Schiff,  F.  G.  Smith,  Flint,  Ranke,  Brunton)  believe 
that  the  transforming  action  of  the  saliva,  commenced  in  the  mouth, 
may  continue  in  the  stomach  in  presence  of  the  gastric  juice.  Others 
(Bernard,  Robin,  Colin)  assert  that  the  action  of  the  saliva  on  starch 
is  arrested  by  the  gastric  juice,  and,  consequently,  does  not  go  on  in 
the  stomach.  This  discrepancy,  no  doubt,  depends  partly  on  different 
modes  of  experimentation  ;  some  writers  contenting  themselves  with 
testing  the  effect  of  dilute  acids  on  the  saliva,  others  using  the  gastric 
juice  itself.  The  proportion  in  which  the  two  secretions  are  mingled 
also  makes  a  difference  in  the  result.  Our  own  observations  lead  to 
the  conclusion  that  gastric  juice  certainly  interferes  with  the  trans- 
forming action  of  saliva,  usually  to  a  very  marked  degree,  when  mingled 
with  it  in  equal  volumes.  If  we  take  fresh  unfiltered  human  saliva, 
shown  by  preliminary  experiment  to  be  capable  of  producing  a  prompt 
sugar-reaction  in  a  solution  of  boiled  starch  at  the  end  of  one  minute, 
mix  it  with  an  equal  volume  of  freshly  collected  gastric  juice  from  the 
dog,  then  add  the  starch-solution,  and  place  the  mixture  in  the  water- 
bath  at  a  temperature  of  38°  C.,  there  is  no  sugar-reaction  whatever 
at  the  end  of  five  minutes,  and  only  an  imperfect  one  in  half  an  hour ; 
while  at  the  end  of  an  hour  there  may  be  distinct  reduction  by  Feh- 
ling's  test.*  But  if  three  volumes  of  gastric  juice  be  added  for  each 
volume  of  saliva,  the  mixture  gives  no  indication  of  sugar  even  at  the 
end  of  an  hour.  It  is  certain  that  the  gastric  juice  is  secreted  normally 
in  much  larger  quantity  than  the  saliva,  and  these  proportions  must  be 
unfavorable  to  the  continuance  of  starch  digestion  in  the  stomach. 

All  observers  agree  that  saliva  is  without  action  on  raw  starch, 
which  may  remain  unchanged  in  contact  with  it,  at  the  temperature 
of  the  body,  for  an  indefinite  time.  But  in  the  herbivorous  animals, 
whose  food  contains  an  abundance  of  raw  starch,  the  salivary  glands 
are  fully  developed,  and  saliva  is  secreted  in  large  quantity.  In  these 

*  In  these  examinations  the  fluid  mixture  is  always  treated  with  animal  charcoal 
previously  to  applying  Fehling's  test ;  otherwise  the  albuminous  matters  of  the 
secretions  would  interfere  with  its  certainty. 


150  FUNCTIONS    OF    NUTRITION. 

animals  the  non-digestion  of  starch  by  saliva  has  been  experimentally 
demonstrated.  Colin*  found  the  farinaceous  matter  of  oats  and  starchy 
roots  recognizable  by  its  iodine  reaction,  after  remaining  in  the  first 
stomach  of  the  ox,  mixed  with  saliva,  for  twenty-four  hours;  and  the 
same  observer  introduced  into  the  interior  of  the  paunch,  through  a 
fistula,  muslin  bags  containing  uncooked  potato  starch,  wrhich  were 
found  in  the  same  cavity,  still  full  of  unaltered  starch,  at  the  end  of 
twenty  and  twenty-two  hours.  In  all  cases,  furthermore,  the  saccha- 
rine transformation  of  starch,  as  we  shall  hereafter  sec,  is  accomplished 
with  great  energy  and  promptitude  by  other  secretions  in  the  small 
intestine. 

It  seems  evident,  therefore,  that  the  sugar-producing  quality  of  the 
saliva  is  not  a  prominent  part  of  its  physiological  action  ;  but  that  it  is 
mainly  useful,  by  its  physical  properties,  in  facilitating  mastication 
and  deglutition. 

It  is  also  subservient,  in  an  indirect  way,  to  the  nervous  influences 
concerned  in  mastication.  This  process  is  aided  and  controlled  in 
great  measure  by  the  sensibilities  of  touch  and  taste,  in  the  tongue  and 
other  parts  of  the  mucous  membrane.  The  taste  notifies  us  of  the  ali- 
mentary character  of  the  food  taken  into  the  mouth,  and  its  sapid 
qualities  must  be  fully  brought  out  before  mastication  is  complete. 
Taste  depends,  for  one  of  its  essential  conditions,  on  a  sufficient  supply 
of  saliva,  since  no  substance  can  produce  an  impression  on  the  gusta- 
tory nerves  unless  it  be  fluid  and  capable  of  absorption.  The  saliva 
produces  this  eifect  on  the  soluble  ingredients  of  the  food,  such  as  sac- 
charine substances,  saline  matters,  acids,  or  alkalies,  and  brings  them 
in  contact  with  the  papillae  of  the  tongue  in  sufficient  quantity  to 
produce  a  gustatory  sensation. 

The  general  sensibility  of  the  tongue  enables  this  organ  to  appre- 
ciate the  physical  condition  of  the  food,  and  its  readiness  for  deglu- 
tition. At  the  same  time  its  muscular  apparatus  provides  for  its 
movement  in  every  direction.  When  the  alimentary  material  is  finally 
reduced,  by  the  saliva  and  mastication,  to  a  pasty  and  homogeneous 
condition,  the  softened  mass  is  collected  from  every  part  of  the  mouth 
by  the  movements  of  the  tongue,  brought  together  upon  its  upper  sur- 
face, and  then  pressed  backward  through  the  fauces  into  the  pharynx 
and  oesophagus.  Here  it  passes  beyond  the  control  of  the  will.  It  is 
then  grasped  by  the  muscular  fibres  of  the  oesophagus,  and  by  a  con- 
tinuous and  rapid  peristaltic  action  is  carried  downward  into  the 
stomach. 

Gastric  Juice. 

The  stomach  is  no  doubt  the  organ  in  which  the  most  important  part 
of  the  digestive  process  is  inaugurated,  and  which  contributes  most 
largely  to  the  chemical  modification  of  the  food.  Its  special  scnvtion 


*  Physiologic  compare  des  Aniiuaux  Dumestiques.     Paris,  1854,  tonic  i.,  p.  G03. 


DIGESTION. 


151 


is  the  gastric  juice,  produced  by  the  glandular  follicles  of  its  mucous 
membrane. 

The  mucous  membrane  of  the  stomach  is  soft  and  vascular,  about  one- 
half  a  millimetre  thick  in  the  cardiac  portion,  thence  increasing  in  thick- 
ness to  one  millimetre  in  the  middle  and  two  millimetres  in  the  pyloric 
portion.  It  presents  an  abundance  of  ridges  or  prominences  about 
one-tenth  of  a  millimetre  in  height,  which  in  the  cardiac  portion  are 
reticulated  with  each  other,  in  the  pyloric  portion  more  isolated  and 
villus-like  in  form.  Its  free  surface  is  covered  with  cylindrical  epi- 
thelium. 

Its  substance  consists  mainly  of  tubular  follicles,  lined  with  glandu- 
lar epithelium,  closely  packed  side  by  side,  their  bases  resting  upon  the 
submucous  layer,  and  their  orifices  opening  upon  its  free  surface.  The 
space  between  them  is  occupied  by  the  capillary  blood-vessels  and  lym- 
phatics, the  terminal  nerve  fibres,  and  a  slight  framework  of  connective 
tissue.  The  gastric  mucous  membrane  has  therefore  the  character  of  a 
gland  spread  out  in  the  membranous  form,  and  surrounding  the  sac-like 
cavity  of  the  organ. 

The  epithelium  cells  lining  the  follicles  are  of  two  kinds.     The  most 
abundant  are  pale,  finely  granular  cells,  about  13  mmm.  in  diameter, 
nearly  or  quite  filling  the  cavity  of  the  follicle  in  its  middle  and  lower 
portions.    The  cells  of  the  other 
variety  are  fewer  in  number,  of 
larger  size,  measuring  about  22 
mmm.  in  diameter,  with  a  dis- 
tinct rounded  form,  often  pro- 
jecting from  the  mass  of  smaller 
cells,  and  causing  varicose-like 
prominences  of  the  contour  of 
the    follicle  (Fig.    24).     These 


FTG.  24. 


cells  are  found  in  both  the  fun- 
dus  and  middle  portion  of  the 
stomach,  especially  in  its  middle 
portion ;  but  they  do  not  exist 
in  the  follicles  of  the  pyloric 
region,  which  contain  cells  of 
the  smaller  variety  alone.  In 
preparations  stained  with  car- 
mine, if  taken  from  the  stomach 
during  the  intervals  of  digestion,  the  smaller  cells  are  tinged  but 
slightly  or  not  at  all,  while  those  of  the  larger  variety  exhibit  a  strong 
pinkish  hue,  showing  a  difference  in  their  organic  substance.  But  in 
specimens  taken  while  digestion  is  going  on,  all  the  cells  are  turgid  and 
granular,  and  the  smaller  ones  not  only  increased  in  size  but  so  altered 
in  constitution  as  to  be  stained  by  the  carmine  solution.  In  prepa- 
rations from  the  fasting  animal,  accordingly,  the  difference  between  the 


GASTRIC  FOLLICLES,  with  large  glandular  cells ;  from 
middle  portion  of  Pig's  Stomach. 


152  FUNCTIONS    OF    NUTRITION. 

two  kinds  of  cells  is  readily  visible  ;  while  in  those  taken  during  diges- 
tion, they  are  hardly  to  be  distinguished  from  each  other.* 

It  is  doubtful  therefore  whether  we  can  infer  any  radical  difference  in 
function  for  different  regions  of  the  stomach  from  the  form  of  their 
glandular  cells.  In  the  follicles  of  the  middle  and  cardiac  portions  the 
two  kinds  of  cells  are  associated,  while  only  the  smaller  kind  are  found 
near  the  pylorus.  But  Ebsteinf  has  shown  that  if  two  digestive  fluids 
be  prepared  by  macerating  the  gastric  mucous  membrane  in  acidulated 
water,  using  for  one  the  middle  portion  and  for  the  other  the  pyloric 
portion,  both  fluids  possess  digestive  properties  which  differ  only  in 
degree.  According  to  a  still  more  decisive  observation  by  Heiden- 
hain,J  the  pyloric  portion,  when  separated  by  preliminary  operation 
from  the  remainder  of  the  stomach,  will  yield  a  secretion  which  com- 
municates digestive  qualities  to  an  acidulated  solution.  The  charac- 
teristic ingredient  of  the  gastric  secretion  seems  to  be  produced  more 
or  less  abundantly  in  all  regions  of  the  stomach,  while  the  differences 
in  function  of  its  different  parts,  so  far  as  they  exist,  relate  to  other 
particulars  not  yet  fully  understood. 

Tic  most  important  early  observations  in  regard  to  the  gastric  juice, 
were  those  of  Beaumont,  §  in  the  case  of  Alexis  St.  Martin,  a  patient 
with  permanent  gastric  fistula,  the  result  of  a  gunshot  wound.  The 
wound  caused  an  opening  at  the  lower  part  of  the  left  chest,  extending 
through  the  diaphragm  into  the  fundus  of  the  stomach.  After  cicatri- 
zation of  the  edges  of  the  wound,  there  remained  a  fistulous  opening, 
about  two  centimetres  in  diameter,  leading  into  the  cavity  of  the 
stomach.  The  orifice  was  usually  closed  from  within  by  a  valvular 
protrusion  of  the  mucous  membrane  ;  but  this  could  be  easily  depressed, 
allowing  the  interior  of  the  stomach  to  be  inspected,  or  its  contents  to 
be  withdrawn  for  examination.  Beaumont's  experiments,  which  were 
continued  at  various  intervals  from  the  year  1825  to  1832,  established 
the  following  important  facts :  First,  that  the  active  agent  in  digestion 
is  an  acid  fluid,  secreted  by  the  walls  of  the  stomach ;  secondlv,  that 
this  fluid  is  poured  out  only  during  digestion,  under  the  influence  of 
food,  or  of  some  artificial  stimulus ;  and  finally,  that  it  will  exert  its 
solvent  action  on  food  outside  the  body,  if  kept  at  the  temperature  of 
38°  C.  He  also  made  investigations  as  to  the  effect  of  various  kinds 
of  stimulus  on  the  secretion  of  the  gastric  juice,  the  rapidity  with 
which  digestion  takes  place,  and  the  digestibility  of  various  kinds  of 
food. 

The  same  person,  with  his  gastric  fistula  unchanged,  after  an  interval 
of  twenty-four  years,  came  under  the  observation  of  Prof.  F.  G.  Smith, 
of  the  University  of  Pennsylvania,  who  again  made  a  series  of  similar 
experiments,  confirming  and  extending  those  of  Beaumont.  Another 

*  Ewald.  Die  Lehre  von  der  Verdauung.     Berlin,  1879,  p.  39. 
f  Archiv.  fur  Mikroscopisehe  Anatomir.     Bonn,  1870,  Band  vi.,  p.  515. 
J  Archiv.  fur  die  gesammte  Physiologic.     Bonn,  1878,  Band  xviii.,  p.  169. 
\  Experiments  and  Observations  upon  the  ( Jastrie  Juiee.     Boston,  1834. 


DIGESTION. 


153 


instance  of  gastric  fistula,  in  an  otherwise  healthy  woman,  the  result 
of  local  inflammation  and  abscess,  occurred  in  Germany  in  1854,  and 
was  investigated  by  Schmidt.*  A  third  case,  in  some  respects  the 
most  remarkable  of  all,  happened  in  France  in  1ST 6.  The  operation 
of  gastrotomy  was  performed  by  Yerneuil,  upon  a  young  man,  for 
impassable  stricture  of  the  oasophagus.  The  patient  recovered  with 
a  permanent  gastric  fistula,  through  which  nourishment  was  success- 
fully administered.  The  following  year  the  case  was  employed  by 
Richet  f  for  observations  on  the  gastric  juice. 

Since  1840,  similar  investigations  have  been  largely  carried  on  by 
the  aid  of  fistulas  artificially  produced  in  various  animals,  the  dog  being 
most  frequently  employed  for  this  purpose.  These  experiments  have 
shown  that  the  ingredients  of  the  gastric  juice,  as  well  as  its  mode  of 
action,  are  essentially  the  same  in  the  carnivorous  and  herbivorous 
animals,  and  in  man.  The  best  mode  of  establishing  a  gastric  fistula 
in  the  dog  is  as  follows:  A  longitudinal  incision,  about  six  centimetres 
long,  is  made  through  the  abdominal  walls  in  the  median  line,  over  the 
great  curvature  of  the  stomach.  The  stomach  is  then  seized  with 
hooked  forceps,  drawn  out  at  the  wound,  and  opened  with  the  point  of 
a  bistoury.  A  short  silver  canula,  about  three  centimetres  long  and 
one  centimetre  in  diameter,  with  a  narrow  flange  at  each  end,  is  inserted 
into  the  wound  in  the  stomach,  the  edges  of  which  are  fastened  around 
it  with  a  ligature,  in  such  a  way  as  to  prevent  the  escape  of  the  gastric 
fluids.  The  stomach  is  then  returned  to  its  place  in  the  abdomen,  the 
external  flange  of  the  canula  resting  upon  the  abdominal  integuments, 
the  edges  of  the  wound  being  drawn  together  by  sutures.  In  a  few 
days  the  ligatures  come  away,  the  wounded  surfaces  unite,  and  the 
canula  is  retained  in  a  permanent  fistula ;  its  flaring  extremities  pre- 
venting it  from  falling  either  out  of  the  abdomen  or  into  the  stomach. 
It  is  closed  externally  by  a  cork,  which  may  be  removed  at  pleasure, 
allowing  the  contents  of  the  stomach  to  be  withdrawn  for  examination. 

Mode  of  Secretion  of  the  Gastric  Juice. — As  a  rule,  the  gastric 
juice  is 'not  a  constant  but  an  occasional  secretion,  being  poured  out 
only  when  food  is  taken  into  the  stomach.  Beaumont  found  it  entirely 
absent  during  the  intervals  of  digestion,  the  stomach  containing  at  that 
time  only  a  little  neutral  or  alkaline  mucus.  He  could  obtain  a  small 
quantity  by  gently  irritating  the  mucous  membrane  with  a  gum-elastic 
catheter,  or  a  glass  rod;  but  on  the  introduction  of  food  the  mucous 
membrane  became  turgid  and  reddened,  a  clear  acid  fluid  collected  in 
drops  beneath  the  mucus  lining  the  walls  of  the  stomach,  and  was  soon 
poured  out  abundantly  into  its  cavity.  Prof.  F.  G.  Smith,  in  his  sub- 
sequent observations  on  Alexis  St.  Martin,  also  found  the  fluids  obtained 
from  the  empty  stomach  invariably  neutral  in  reaction ;  while  during 
digestion  they  were  always  acid.  Other  observers,  in  experimenting 
on  the  dog,  have  found  more  or  less  acid  reaction  always  present  at  the 

*  Annalen  der  Chemie  und  Pharmacie.     Heidelberg,  1854,  p.  42. 

f  Comptes  Kendus  de  1' Academic  des  Sciences.    Paris,  1877,  tome  Ixxxiv.,  p.  450. 


154  FUNCTIONS    OF    NUTRITION. 

surface  of  the  mucous  membrane.  According  to  our  own  observations, 
the  irritability  of  the  gastric  mucous  membrane,  and  the  readiness  with 
which  the  flow  of  gastric  juice  may  be  excited,  varies  considerably  in 
different  animals  of  the  same  species.  In  dogs,  we  have  found  in  one 
instance  that  the  gastric  juice  was  always  entirely  absent  in  the  inter- 
vals of  digestion ;  the  mucous  membrane  presenting  either  a  neutral 
or  slightly  alkaline  reaction.  In  this  animal,  which  was  perfectly 
healthy,  the  secretion  could  not  be  excited  by  any  artificial  means,  such 
as  glass  rods,  metallic  catheters,  or  the  like ;  but  only  by  the  stimulus 
of  ingested  food.  Indigestible  pieces  of  tendon,  introduced  through 
the  fistula,  were  expelled  in  a  few  minutes,  without  exciting  the  flow 
of  a  single  drop  of  acid  fluid ;  while  pieces  of  fresh  meat,  introduced 
in  the  same  way,  produced  at  once  an  abundant  supply.  In  other 
instances  the  introduction  of  metallic  catheters  or  glass  rods  into  the 
empty  stomach  has  produced  a  scanty  flow  of  gastric  juice ;  and  in 
dogs  killed  by  section  of  the  medulla  oblongata,  we  have  usually, 
though  not  always,  found  the  gastric  mucous  membrane  with  a  dis- 
tinctly acid  reaction,  even  after  an  abstinence  of  six,  seven,  or  eight 
days.  Under  these  circumstances  there  is  never  any  considerable 
amount  of  fluid  in  the  stomach ;  but  only  enough  to  moisten  the 
mucous  membrane,  and  give  it  an  acid  reaction. 

The  gastric  juice  obtained  by  irritating  the  stomach  with  a  metallic 
catheter  is  not  sufficient  in  quantity  for  extended  experiments.  For 
that  purpose,  the  animal  should  be  fed,  after  a  fast  of  twenty-four 
hours,  with  fresh  lean  meat,  slightly  hardened  by  short  boiling,  in 
order  to  coagulate  the  fluids  of  the  muscular  tissue,  and  prevent  their 
mixing  with  the  gastric  secretion.  Usually  no  effect  is  apparent 
within  five  minutes  after  the  introduction  of  food.  At  the  end  of 
that  time  the  gastric  juice  begins  to  flow  slowly  and  in  drops.  It  is  at 
first  colorless,  but  soon  acquires  a  slight  amber  tinge.  It  then  runs 
more  freely,  usually  in  drops,  but  often  for  a  few  seconds  in  a 
continuous  stream.  In  this  way,  from  60  to  75  cubic  centimetres 
may  be  collected  in  the  course  of  fifteen  minutes.  Afterward  it 
becomes  somewhat  turbid  with  the  debris  of  disintegrated  food, 
from  which  it  may  be  separated  by  filtration.  After  three  hours, 
it  continues  to  run  freely,  but  much  thickened  and  grumous  in  con- 
sistency, from  the  admixture  of  alimentary  debris.  In  six  hours  it  is 
less  abundant,  and  in  eight  hours  has  become  very  scanty.  It  ceases 
to  flow  altogether  in  from  nine  to  twelve  hours,  according  to  the 
quantity  of  food  taken.  For  purposes  of  examination,  the  fluid 
drawn  during  the  first  fifteen  minutes  after  feeding  should  be  col- 
lected, and  at  once  separated  by  filtration  from  accidental  impurities. 

Physical  Properties  and  Composition  of  the  Gastric  Juice. — 
Gastric  juice  obtained  by  this  method  is  a  clear,  colorless,  or  faintly 
amber-colored  fluid,  of  watery  consistency  and  acid  reaction.  Its 
specific  gravity  does  not  vary  much  from  1010.  It  becomes  slightly 
opalescent  on  boiling. 


DIGESTION.  155 

The  following  is  the  composition  of  the  gastric  juice  of  the  dog, 
based  on  a  comparison  of  analyses  by  Lehmann,  Blondlot,  Otto,  and 
Bidder  and  Schmidt. 

COMPOSITION  OF  GASTRIC  JUICE. 

Water    ...........  975.00 

Free  acid       ........  4  ^g 

Pepsine         ........        !  15*00 

Sodium  chloride    ..........  1  YO 

Potassium    "         ......  ^  Qg 

Calcium        "         ......  Q  2Q 

Ammonium  " 


Lime  phosphate     ......  1  48 

Magnesium  "        .        ...... 

Iron  " 


1000.00 

Schmidt,  in  the  case  which  fell  under  his  observation,  found  the  gas- 
tric juice  of  man  similar  in  constitution  to  the  above,  except  that  it 
contained  a  larger  proportion  of  water  and  a  smaller  proportion  of  free 
acid  and  pepsine,  as  well  as  of  solid  ingredients  generally.  In  the  case 
investigated  by  Richet,  the  amount  of  acid  was,  on  the  average,  l.f 
per  thousand  parts;  its  minimum  being  0.5  and  its  maximum  3.2. 
Such  differences  may  therefore  exist  between  individuals,  or  even  in 
the  same  individual  at  different  times;  depending  no  doubt  on  the 
more  or  less  rapid  secretion  of  the  watery  parts.  Observations  on 
the  dog  show  that  the  proportion  of  solid  ingredients  is  usually  less 
when  the  secretion  is  abundant,  and  greater  when  it  is  in  small  quan- 
tity. In  either  case  the  essential  constituents  are  the  same. 

The  most  striking  physical  property  of  the  gastric  juice  is  its  acid 
reaction,  by  which  it  is  distinguished  from  all  the  other  digestive  secre- 
tions and  internal  fluids  of  the  body.  This  property  depends  on  the 
presence  of  its  free  acid.  Notwithstanding  that  all  observers  have 
recognized  in  the  gastric  juice  a  distinct  acidity,  a  singular  difference 
of  opinion  still  exists  as  to  the  particular  body  which  gives  it  this 
reaction,  and  especially  whether  it  be  a  mineral  or  an  organic  acid. 
Repeated  analyses  have  been  made  by  different  methods,  and  each 
new  result  has  been  claimed  as  decisive  on  the  one  side  or  the  other. 
Many  observers  (Prout,  Dunglison,  Enderlin,  Schmidt,  Ewald,  Hoppe- 
Seyler)  regard  the  free  acid  of  the  gastric  juice  as  hydrochloric  acid. 
Their  conclusion  is  mainly  based  on  the  fact  that  the  total  quantity  of 
hydrochloric  acid  obtainable  from  the  secretion  is  more  than  sufficient 
to  saturate  all  the  alkaline  and  earthy  bases  which  it  contains.  Others 
(Lehmann,  Leuret  and  Lassaigne,  F.  G.  Smith,  Laborde,  Bernard  and 
Barreswil)  consider  the  acid  ingredient  to  be  lactic  acid.  In  support 
of  this  view  they  adduce  certain  reactions  of  the  gastric  juice  which 
do  not  belong  to  solutions  of  hydrochloric  acid,  such  as  precipitation 
of  lime  oxalate  on  the  addition  of  a  little  oxalic  acid,*  and  the  fact  that 

*  Bernard.     Lepons  de  Physiologic  Experimentale.     Paris,  1856,  p.  396. 


156  FUNCTIONS    OF    NUTRITION. 

gastric  juice  does  not  convert  cane-sugar  into  glucose  at  a  boiling 
temperature  as  hydrochloric  acid  would  do.*  It  is  acknowledged 
that  both  the  acids  in  question  may  be  obtained  from  gastric  juice 
by  distillation  and  analysis ;  f  but  it  is  considered  doubtful  whether 
the  hydrochloric  may  not  be  liberated  by  decomposition,  or  the  lactic 
produced  by  fermentation,  during  the  process.  Finally,  Richet  J  has 
investigated  the  subject  by  a  method  which  avoids  prolonged  chemical 
manipulation.  This  method  depends  on  the  comparative  solubility  in 
ether  of  organic  and  mineral  acids.  The  organic  acids  are  readily 
soluble  in  this  menstruum,  and  ten  volumes  of  ether,  shaken  up  with 
one  volume  of  a  watery  solution,  will  remove  from  it  one-half  the  lactic 
acid  which  it  contains.  The  mineral  acids,  on  the  other  hand,  are  but 
slightly  soluble  in  the  same  fluid ;  and  it  requires  500  volumes  of  ether 
to  extract  from  a  watery  solution  one-half  its  acid  ingredient,  should 
this  be  hydrochloric  acid.  From  experiments  of  this  kind  the  author 
concludes  that  the  fresh  gastric  juice,  unmixed  with  food,  contains 
almost  exclusively  hydrochloric  acid;  the  proportion  being  not  more 
than  one  part  of  lactic  acid  to  twenty  parts  of  hydrochloric ;  but  that 
if  kept  for  some  days  the  organic  acid  may  so  increase  as  to  prepon- 
derate over  the  mineral ;  and  furthermore,  that  gastric  juice,  if  mixed 
with  food,  may  form  organic  acids  during  digestion  to  the  amount  of 
one-third  or  one-half  the  mineral  acid  present.  The  subject,  therefore, 
is  not  altogether  free  from  obscurity. 

It  is  certain,  however,  that  the  normal  free  acid  of  the  gastric  juice, 
if  neutralized,  may  be  replaced  by  either  lactic  or  hydrochloric  acid 
without  impairing  its  digestive  properties.  Other  acid  bodies,  both 
mineral  and  organic,  as  dilute  sulphuric,  nitric,  or  acetic  acids  are 
also  available  for  the  purpose,  though  much  less  so  than  the  fore- 
going ;  while  phosphoric,  oxalic,  and  tartaric  acids,  according  to  Leh- 
mann,  are  nearly  inert  in  this  respect. 

The  remaining  characteristic  ingredient  of  the  gastric  juice  is  its 
albumenoid  matter,  known  under  the  name  of  pepsine.  This  is  the 
special  ferment  produced  by  the  gastric  follicles,  to  which  the  peculiar 
digestive  properties  of  the  secretion  are  due.  It  is  precipitable  from 
the  gastric  juice  by  alcohol  in  excess,  and  after  precipitation  may  be 
rcdissolvcd  in  water  with  its  qualities  unchanged.  Gastric  juice  is 
utially  an  acidulated  solution  of  pepsine.  Both  the  ferment  and 
the  acid  must  be  present  in  order  that  the  secretion  may  exert  its 
digestive  power.  If  fresh  gastric  juice  be  neutralized  by  the  addi- 
tion of  an  alkali  or  alkaline  carbonate,  it  becomes  inactive  notwith- 
standing the  presence  of  pepsine;  but  its  activity  may  bo  restored  by 
acidulation.  On  the  other  hand,  gastric  juice  from  which  the  pepsine 
has  been  thrown  down,  or  in  which  it  has  been  rendered  inactive  by 
boiling,  has  no  digestive  power  although  its  acidity  remains. 

*  Revue  des  Sciences  Me*dicales.  Paris,  1878,  tome  xii.,  p.  715. 
f  Iloppe-Seyler.  Physiolo^ische  Chemie.  Berlin,  1878,  p.  215. 
JComptes  Rendus  de  1'  Academic  des  Sciences.  Paris,  1877,  tooie  Ixxxiv.,  p.  1514. 


DIGESTION.  157 

Both  the  essential. constituents  of  the  gastric  juice  are  produced  by 
the  mucous  membrane,  but  their  mode  of  production  is  different.  Pep- 
sine  is  continuously  formed  by  the  nutritive  process,  and  accumulates 
during  the  intervals  of  digestion  in  the  glandular  cells.  The  free  acid, 
on  the  other  hand,  appears  in  quantity  only  at  the  time  of  digestion, 
and  is  poured  out  with  the  watery  constituents  of  the  secretion.  There 
is  evidence  that  it  is  not  present  in  the  immediate  product  of  the  glan- 
dular cells,  but  is  produced  by  a  rapid  change  in  the  fluid  after  secretion. 
The  mucous  membrane  is  never  distinctly  acid  in  its  deeper  and  middle 
parts,  but  only  on  its  free  surface.  This  was  shown  by  Bernard,*  who 
injected  into  the  jugular  vein  of  a  rabbit  two  solutions,  one  of  iron  lac- 
tate,  the  other  of  potassium  ferrocyanide.  These  salts  would  remain 
unaltered  in  neutral  or  alkaline  fluids,  but  in  presence  of  a  free  acid 
would  unite  to  form  Prussian  blue  (iron  ferrocyanide).  On  killing 
the  animal,  three-quarters  of  an  hour  afterward,  no  blue  coloration 
was  found  anywhere  excepting  in  the  stomach ;  and  in  this  organ  it 
was  confined  to  the  free  surface  of  the  mucous  membrane,  not  being 
perceptible  in  the  substance  of  the  glandules.  As  both  salts  must 
have  exuded  from  the  blood-vessels  of  the  mucous  membrane,  it  is 
evident  that  it  was  only  at  or  near  its  upper  surface  that  they  met 
with  sufficient  free  acid  to  cause  their  combination.  According  to 
Bruntonf  a  horizontal  section  through  the  lower  part  of  the  gastric 
glands  of  the  pigeon,  if  tested  by  litmus-paper,  shows  a  neutral  or 
extremely  weak  acid  reaction,  while  the  inner  surface  of  the  stomach 
is  strongly  acid.  The  materials  of  the  free  acid  of  the  gastric  juice 
are  therefore  furnished  by  the  alkaline  blood ;  but  the  acid  itself  origi- 
nates by  some  change  in  the  products  of  exudation. 

A  necessary  condition  for  the  action  of  the  gastric  juice  is  a  certain 
temperature.  It  may  go  on  more  or  less  rapidly  within  varying  limits, 
but  its  most  favorable  teniperature  is  that  of  the  living  body.  It  is 
suspended  at  or  near  the  freezing-point,  becomes  more  active  with  the 
increase  of  warmth,  and  is  at  its  maximum  about  38°  C. ;  above  which 
it  again  diminishes,  and  is  totally  arrested  at  the  boiling  temperature. 
The  favorable  influence  of  moderate  warmth  has  been  shown  by  Schiff,  J 
who  made  two  acidulated  digestive  infusions,  and  placed  in  each  the 
same  quantity  of  coagulated  albumen ;  one  of  the  infusions  being 
allowed  to  remain  at  a  temperature  varying  from  10°  to  1*7°  C.,  the 
other  being  introduced,  in  a  closed  glass  tube,  into  the  stomach  of  a 
living  dog.  The  second  was  found  to  have  digested  in  six  hours  as 
much  albumen  as  the  first  at  the  end  of  three  weeks.  . 

A  further  peculiarity  of  the  gastric  juice  is  its  resistance  to  putre- 
faction. While  other  animal  fluids,  as  the  saliva,  bile,  pancreatic  juice, 
mucus,  and  blood,  enter  into  putrefaction  with  great  readiness,  gastric 
juice  may  remain  exposed  to  the  air  at  ordinary  temperatures  for 

*  Liquides  de  I'Orgamsme.     Paris,  1859,  tome  ii.,  p.  375. 

f  Handbook  for  the  Physiological  Laboratory.     Philadelphia,  1873,  p.  491. 

j  Le9ons  sur  la  Physiologic  de  la  Digestion.     Paris,  1867,  tome  ii.,  p.  19. 


158  FUNCTIONS    OF    NUTRITION. 

months  without  developing  any  putrescent  odor  or  losing  its  character- 
istic properties.  It  becomes  somewhat  darker  in  color,  and  after  a  time 
deposits  a  brownish  sediment,  but  retains  its  acid  reaction  and  its  power 
of  digesting  albuminous  matters.  It  will  even  arrest  putrefactive 
changes  which  have  already  begun  in  organic  substances ;  and  conse- 
quently putrefaction  does  not  go  on  in  the  living  stomach.  Beaumont 
preserved  fragments  of  meat  unaltered  for  a  month  in  gastric  juice, 
while  other  portions  kept  in  saliva  were  putrefied  in  ten  days.  Spal- 
lanzani  found  in  the  stomach  of  a  viper  the  body  of  a  lizard  which  had 
remained  there  for  sixteen  days  without  putrefactive  alteration ;  and 
similar  observations  have  been  made  by  other  physiologists.  Accord- 
ing to  Richet,  the  antiseptic  property  of  gastric  juice  depends  entirely 
on  its  free  acid,  and  not  in  any  degree  on  its  organic  ferment. 

Pepsine  Extracts,  and  Artificial  Digestive  Fluids. — As  the  imme- 
diate source  of  the  gastric  juice  is  the  mucous  membrane  of  the  stomach, 
the  idea  was  early  suggested  that  a  similar  fluid  might  be  extracted 
from  its  tissue  after  death.  Experiments  of  this  kind  have  been  made 
in  various  ways  since  1834 ;  and  they  have  demonstrated  that  the 
gastric  mucous  membrane,  taken  from  the  recently-killed  animal,  may 
yield  a  solution  containing  pepsine,  which,  in  the  presence  of  a  dilute 
acid,  at  the  proper  temperature,  has  the  power  of  dissolving  solid  albu- 
minous matters.  Such  solutions  act  as  artificial  digestive  fluids,  and 
by  their  use  much  additional  light  has  been  thrown  on  the  digestive 
process.  They  are  obtained,  according  to  Lehmann's  method,  by 
immersing  the  cleansed  mucous  membrane  in  water  for  an  hour  or 
two,  until  moderately  softened,  when  its  glandular  parts  are  removed 
by  scraping  with  a  spatula,  placed  in  acidulated  water,  the  mixture  kept 
for  an  hour  at  the  temperature  of  35°  C.  and  the  fluid  then  filtered. 
Or  the  mucous  membrane  may  be  cut  into  small  pieces,  and  kept  in  a 
large  quantity  of  acidulated  water  at  35°  C.  until  the  glandular  tissue 
is  fully  disintegrated,  when  the  mixture  is  filtered  and  the  clear  liquid 
used  for  experiment.  The  second  process  yields  a  fluid  which  has  con- 
siderable digestive  activity,  but  is  contaminated  with  products  of  the 
digestion  of  the  stomach  tissues.  The  most  convenient  and  most 
widely  employed  method  is  that  of  Yon  Wittich,  which  consists  in 
extracting  the  mucous  membrane  with  glycerine.  It  has  the  advantage 
that  glycerine,  in  the  concentrated  form,  while  it  dissolves  out  the  pep- 
sine,  arrests  completely  both  digestive  and  putrescent  alterations.  The 
extract  finally  obtained  is  therefore  free  from  the  products  of  digestion, 
and  may  be  kept  .indefinitely  for  experimental  use.  In  this  process  the 
mucous  membrane,  cut  into  small  pieces  and  freed  from  water  by  a 
short  immersion  in  alcohol,  is  placed  in  a  quantity  of  glycerine  suffi- 
cient to  cover  it  and  macerated  for  eight  days  at  ordinary  temperatures, 
after  which  the  glycerine  solution  is  strained  otf.  This  glycerine 
extract  contains  pepsine,  and  a  little  of  it  added  to  acidulated  water 
forms  an  efficient  digestive  fluid.  If  desired,  the  pepsine  may  l»e  pre- 
cipitated from  the  glycerine  solution  by  alcohol  in  excess,  removed  by 


DIGESTION.  159 

filtration  in  a  comparatively  pure  condition,  and  then  redissolved  in 
water  or  an  acidulated  solution.  The  proportion  of  acid  best  adapted 
for  digestion  is  about  2  parts  hydrochloric  acid  to  1000  parts  of  water. 
The  most  convenient  substance  for  showing  the  digestive  powers  of 
such  a  fluid  is  coagulated  fibrine,  obtained  by  whipping  fresh  blood, 
and  cleansed  from  coloring  matter  by  repeated  washing  with  cold  water. 

Physiological  Action  of  the  Gastric  Juice. — If  gastric  juice  from  the 
living  animal,  or  an  acidulated  solution  of  pepsine  prepared  by  the 
above  method,  be  tested  at  the  temperature  of  38°  C.  with  different 
organic  matters,  it  will  be  found  that  its  action  is  confined  to  those  of 
a  single  class.  It  has  no  effect  upon  starches  or  fats ;  but  albuminous 
matters,  such  as  coagulated  fibrine,  caseine,  or  white  of  egg,  or  tissues 
mainly  composed  of  albuminous  substances,  are  softened  and  liquefied, 
and  finally  digested.  The  process  by  which  this  change  takes  place  is 
twofold,  accomplished  by  the  successive  or  simultaneous  action  of  the 
tAvo  essential  constituents  of  the  secretion.  The  first  effect  is  produced 
under  the  influence  of  the  free  acid,  by  which  the  albuminous  matter 
is  converted  into  syntonine.  This  substance  is  soluble  in  dilute  acids, 
and  therefore  assumes  the  liquid  state  in  an  acidulated  solution ;  but  it 
is  not  soluble  in  pure  water  nor  in  solutions  of  the  neutral  salts,  and  it 
may  accordingly  be  precipitated  by  neutralization  with  an  alkali.  So 
far,  the  modification  of  albumen  in  the  digestive  act  is  comparatively 
simple.  Its  further  change  is  due  to  the  presence  of  pepsine.  By  the  • 
influence  of  this  substance,  acting  as  a  ferment,  the  modified  albu- 
minous matter  is  transformed  into  peptone.  Since  peptone  is  soluble 
in  pure  water  and  in  neutral  solutions,  as  well  as  in  dilute  acids  and 
alkalies,  it  retains  the  liquid  form  whatever  may  be  the  reaction  of  the 
fluid  in  which  it  is  contained.  The  non-precipitation  of  the  albumenoid 
matter,  on  neutralizing  the  solution,  is  therefore  the  indication  and 
measure  of  its  complete  transformation  in  the  digestive  process. 

As  one  of  the  distinctive  features  of  peptone  is  its  diffusibility  through 
animal  membranes,  it  represents  the  condition  of  albumen  when  pre- 
pared for  absorption  by  the  blood-vessels.  It  is  not  coagulable  by  heat, . 
the  mineral  acids,  nor  by  potassium  ferrocyanide,  but  is  thrown  down 
from  its  solutions  by  alcohol  in  excess. 

The  characters  of  peptone  are  the  same,  or  nearly  so,  whether  it  be^ 
derived  from  coagulated  fibrine,  albumen,  caseine,  or  an  organized 
structure,  like  muscular  or  connective  tissue.  According  to  Henniger, 
the  only  perceptible  difference  is  in  its  rotary  power  on  polarized  light. 
All  varieties  of  peptone  in  solution  deviate  the  plane  of  polarization 
toward  the  left ;  the  amount  of  rotation  being  greatest  for  albumen 
peptone,  while  that  for  fibrine  peptone  is  the  least.  As  to  its  nature, 
it  is  the  prevalent  opinion  among  physiological  chemists,  that  peptone 
is  a  product  of  hydration ;  the  albuminous  molecule  uniting  with  the 
elements  of  water  under  the  influence  of  the  gastric  ferment.  This 
view  is  partly  based  on  the  elementary  composition  of  peptone  and  its 
power  of  uniting  with  acids  and  bases,  as  compared  with  albumen.  It 


160  FUNCTIONS    OF    NUTRITION. 

is  also  sustained  by  the  experiments  of  Ilenniger,*  who  subjected  pep- 
tone to  a  process  of  dehydration  by  means  of  anhydrous  acetic  acid  at 
80°  C.,  obtaining  as  the  result  an  albumen-like  substance  coagulable  by 
heat. 

Digestion  of  the  Stomach  Tissues  by  Gastric  Juice. — As  the  gastric 
juice,  or  acidulated  pepsine  solutions,  can  dissolve  the  substance  of  all 
albuminous  tissues,  they  have  the  same  effect  on  the  walls  of  the 
stomach  itself.  If  the  gastric  mucous  membrane  be  macerated  in  acid- 
ulated water  at  the  temperature  of  38°  C.,  the  mixture  no  sooner  absorbs 
pepsine  from  the  gastric  follicles  than  it  becomes  digestive,  and  con- 
sequently dissolves  the  tissue  of  the  membrane  itself.  It,  therefore, 
requires  some  explanation  to  understand  how  the  stomach  can  produce 
a  secretion  which  is  capable  of  destroying  its  own  substance.  This  is, 
no  doubt,  due  to  the  manner  in  which  the  secretion  takes  place.  We 
have  already  seen  that  pepsine  is  a  constant  ingredient  of  the  glandular 
cells  formed  in  the  intervals  of  digestion,  while  the  free  acid  is  produced 
by  a  sudden  exudation,  on  the  introduction  of  food.  The  acid  is  also 
poured  out  only  near  the  orifices  of  the  glandular  follicles,  being  at 
once  discharged  into  the  cavity  of  the  organ  and  absorbed  by  the 
alimentary  mass.  The  gastric  juice  can  exert  its  digestive  power  only 
in  the  presence  of  an  acid  reaction,  and  the  mucous  membrane  is  conse- 
quently protected  from  its  influence  by  the  alkalescence  of  its  intersti- 
tial fluid,  maintained  by  the  circulation  of  the  blood.  The  nature  of 
the  change  by  which  a  free  acid  is  produced  from  the  constituents  of 
the  alkaline  blood  is  not  certainly  known,  but  there  is  no  doubt  that 
this  acid  first  appears  after  the  exudation  of  the  fluids,  and  it  is  also 
plain  that  its  liberation  must  increase  for  the  moment  the  alkalinity  of 
the  remaining  constituents  of  the  mucous  membrane. 

But  after  death  self-digestion  of  the  stomach  is  not  an  unfrequent 
occurrence.  It  does  not  take  place  in  the  majority  of  cases,  because,  as 
a  rule,  digestion  has  been  suspended  during  the  last  hours  of  life,  and 
the  stomach  contains  little  or  no  gastric  juice.  On  the  other  hand, 
when  death  takes  place  suddenly,  soon  after  the  ingestion  of  food,  ;md 
when  the  body  is  not  too  rapidly  cooled,  the  accumulated  gastric  juice 
acts  on  the  walls  of  the  stomach  as  well  as  on  the  food  which  it  con- 
tains. Owing  to  the  stoppage  of  the  circulation,  the  local  alkalescence 
of  the  fluid  is  no  longer  maintained,  and  the  free  acid  at  last  prepon- 
derates over  the  blood  remaining  in  the  capillary  vessels.  The  mucous 
membrane,  thus  imbibed  with  an  active  digestive  fluid,  in  the  course  of 
ten  or  twelve  hours  may  be  so  softened  and  disintegrated  as  to  expose 
the  submucous  connective  tissue ;  and  occasionally  all  the  coats  of  the 
organ  have  been  found  destroyed,  with  a  perforation  into  the  peritoneal 
cavity.  After  death,  accordingly,  the  tissues  of  the  stomach  arc  aflectcd 
by  the  gastric  juice  in  the  same  way  as  the  albuminous  ingredients  of 
the  food. 

*  Revue  des  Sciences  Me"dicales.     Paris,  1878,  tome  xii.,  p.  721. 


DIGESTION.  161 

Daily  Quantity  of  the  Gastric  Juice.— The  quantity  of  gastric 
juice  secreted  during  a  given  time,  like  that  of  the  saliva,  varies  much 
according  to  the  condition  of  the  secreting  organ.  An  exact  estimate 
of  its  daily  amount  is  difficult  for  several  reasons.  First,  if  excited  by 
artificial  irritation  of  the  gastric  mucous  membrane,  its  quantity  is  not 
so  abundant  as  when  produced  by  the  natural  stimulus  of  food ;  sec- 
ondly, if  excited  by  the  introduction  of  food,  a  part  of  it  is  absorbed 
by  the  alimentary  material,  and  consequently  cannot  be  collected  for 
measurement ;  and  thirdly,  the  quantity  collected  during  a  short  period 
does  not  indicate  the  rate  of  production  for  the  rest  of  the  twenty-four 
hours,  because  its  secretion  is  influenced  by  the  state  of  the  digestive 
process.  Neither  can  we  draw  from  a  fistula  all  the  gastric  juice 
obtainable  during  twenty-four  hours,  and  consider  that  as  representing 
the  normal  daily  amount ;  because  we  should  be  taking  away  a  quantity 
of  fluid  which  is  naturally  retained  for  reabsorption  by  the  blood-vessels, 
and  its  supply  would  be  consequently  diminished.  But  notwithstand- 
ing these  difficulties,  sufficient  facts  have  been  collected  to  show  that 
the  gastric  juice  is  far  more  abundant  than  the  other  digestive  fluids. 
Beaumont  obtained  from  the  stomach  of  St.  Martin,  by  the  introduction 
of  a  gum-elastic  catheter,  44  grammes  of  gastric  juice  in  fifteen  minutes. 
We  have  often  collected  from  a  medium-sized  dog,  at  the  beginning 
of  digestion,  from  60  to  15  grammes  in  the  same  time.  Bidder  and 
Schmidt,  in  a  dog  weighing  15.5  kilogrammes,  obtained  by  separate 
experiments,  consuming  in  all  twelve  hours,  793  grammes  of  gastric 
juice.  If  these  experiments,  as  is  probable,  indicate  the  average  rate 
of  secretion  during  the  day,  the  entire  quantity  for  twenty-four  hours, 
in  an  animal  of  that  size,  wrould  be  1586  grammes;  or  about  100 
grammes  for  every  kilogramme  of  bodily  weight.  By  applying  this 
calculation  to  a  man  of  ordinary  size  the  authors  estimate  the  aver- 
age daily  quantity  of  gastric  juice  in  man  at  about  6500  grammes. 
Schmidt,  in  his  case,  already  quoted,  of  a  woman  with  gastric  fistula, 
obtained,  as  the  mean  result  of  several  observations,  580  grammes  of 
gastric  juice  in  the  course  of  an  hour.  The  secretion,  however,  was 
much  poorer  in  characteristic  ingredients  than  that  usually  obtained 
from  the  dog,  and  was  also  inferior  in  digestive  power. 

Another  method  for  estimating  the  daily  quantity  of  gastric  juice 
is  to  ascertain  the  amount  required  for  digesting  the  albuminous  food. 
According  to  Lehmann,*  one  gramme  of  coagulated  albumen,  calculated 
as  dry,  requires  for  its  solution  20  grammes  of  gastric  juice.  As  the 
average  daily  consumption  of  albuminous  matter  in  man  is  130 
grammes,  this  would  require  2600  grammes  of  gastric  juice  per 
day.  Our  own  observations  on  the  digestibility  of  fresh  meat  make 
the  daily  requirement  higher.  A  weighed  quantity  of  fresh  lean  meat, 
containing  18  per  cent,  of  water  and  22  per  cent,  of  solid  ingredients, 
was  cut  into  small  pieces,  and  digested  for  ten  hours,  with  frequent 

*  Physiological  Chemistry.     London,  1853,  vol.  ii.,  p.  53. 
L 


162  FUNCTIONS    OF    NUTRITION. 

agitation,  in  a  measured  quantity  of  fresh  gastric  juice  at  the  tempera- 
ture of  38°  C.  The  liquefied  portions  were  then  filtered  away,  the 
residue  evaporated  to  dryness,  and  the  quantity  of  fresh  meat  remain- 
ing undissolved  thus  calculated  from  the  percentage  of  its  solid  ingredi- 
ents. In  this  way  it  was  found  that  one  gramme  of  meat  had  been 
liquefied  by  13.5  grammes  of  the  digestive  fluid.  We  have  already 
seen  (p.  129)  that  a  man  consumes,  in  his  ordinary  daily  ration,  453 
grammes  of  meat ;  which  would  require  for  complete  digestion  a  little 
over  6000  grammes  of  gastric  juice.  This  agrees  very  nearly  with 
the  estimate  of  Bidder  and  Schmidt  given  above ;  and  if  gastric 
juice  were  the  only  digestive  fluid  acting  on  the  food,  we  mi.irht 
accept  it  as  correct.  But  below  the  stomach  other  secretions  take 
part  in  the  digestive  process ;  and  some  of  them,  especially  the  pan- 
creatic juice,  have  a  certain  action  on  albuminous  matters,  and  may 
facilitate  considerably  their  solution  in  the  intestine.  For  the  partial 
solution  of  meat,  the  disintegration  of  its  fibres,  and  its  reduction  to 
a  soft,  grumous,  or  semi-fluid  consistency,  Beaumont  found  a  much 
smaller  quantity  of  gastric  juice  sufficient.  In  one  experiment,  one 
gramme  of  cooked  meat  was  disintegrated  by  2.5  grammes,  and  in 
another  by  1.83  grammes  of  gastric  juice.  Its  complete  solution 
would  of  course  require  a  larger  quantity. 

These  data  are  insufficient  for  determining  the  precise  quantity  of 
gastric  juice  required  for  digestion.  But  if  we  allow  sufficient  weight 
to  all  the  observations  on  this  subject,  it  is  evidently  very  abundant ; 
and  it  would  not  be  extravagant  to  estimate  its  quantity  as  at  least 
3000  grammes  per  day. 

Process  of  Stomach  Digestion. — The  first  effects  of  the  introduction 
of  food  into  the  stomach,  according  to  all  observers,  arc  increased  vas- 
cularity  of  its  mucous  membrane,  a  slight  elevation  of  its  temperature, 
and  the  exudation,  in  greater  or  less  abundance,  of  its  acid  secretion. 
At  the  same  time  the  peristaltic  movement  begins  to  take  place,  by 
the  alternate  contraction  and  relaxation  of  the  longitudinal  and  cir- 
cular fibres  of  the  muscular  coat.  This  motion  is  minutely  described 
by  Beaumont,  who  examined  it,  both  by  watching  the  movements  of 
the  food  through  the  gastric  fistula,  and  by  introducing  into  the  stomach 
the  bulb  and  stem  of  a  thermometer.  According  to  his  observations, 
the  food,  after  entering  the  cardiac  orifice,  is  first  carried  to  the  left 
into  the  fundus  of  the  stomach,  thence  downward  and  along  the  great 
curvature  to  the  pyloric  portion.  In  this  region  there  was  often  a 
constriction,  by  which  the  thermometer  was  gently  grasped  and  drawn, 
with  a  twisting  motion,  toward  the  pylorus.  In  a  moment  or  two,  it  was 
again  released  and  carried,  together  with  the  food,  along  the  small 
curvature  of  tin-  origan  to  its  cardiac  extremity  This  circuit  was 
repeated  so  long  as  any  food  remained  in  the  stomach;  but  toward 
the  end  of  digestion  it  became  less  active,  and  the  stomach,  when  com- 
pletely empty,  returned  to  its  ordinary  quiescent  condition. 

The  muscular  action  of  the  stomach  during  digestion  in  the  dog  may 


DIGESTION.  163 

be  observed  by  means  of  a  gastric  fistula.  A  metallic  catheter,  intro- 
duced through  the  fistula  when  the  stomach  is  empty,  must  usually 
be  held  in  place,  or  it  will  fall  out  by  its  own  weight.  But  on  the 
introduction  of  food,  the  catheter  is  grasped  and  retained  with  some 
force,  by  the  contraction  of  the  muscular  coat.  A  twisting  motion 
of  its  extremity  may  also  be  frequently  observed,  similar  to  that 
described  by  Beaumont.  This  peristaltic  action,  though  quite  gentle, 
is  sufficient  to  produce  a  churning  movement  of  the  food,  by  which  its 
different  portions  are  shifted  from  side  to  side,  and  the  gastric  juice 
made  to  penetrate  thoroughly  all  its  parts.  It  thus  receives  a  more 
rapid  and  uniform  digestion  of  its  various  ingredients.  The  move- 
ment is  one  which  cannot  be  fully  imitated  in  experiments  on  artificial 
digestion  in  test-tubes ;  and  the  process,  under  these  circumstances,  is 
consequently  less  rapid  than  in  the  interior  of  the  stomach. 

The  alimentary  matters,  thus  incorporated  with  the  gastric  juice,  are 
disintegrated  by  the  liquefaction  of  their  albuminous  ingredients. 
Bread  consists  mainly  of  hydrated  starch  and  solid  gluten.  By  diges- 
tion the  gluten  is  converted  into  soluble  peptone,  the  starch  being 
thus  set  free,  and  the  whole  reduced  to  a  diffluent  condition.  The 
same  effect  is  produced  on  bread  subjected  to  the  action  of  gastric 
juice  in  a  test-tube,  the  gluten  passing  into  a  liquid  condition,  while 
a  deposit  of  unaltered  starch  settles  at  the  bottom.  Cheese,  consisting 
of  coagulated  caseine  and  milk  globules,  undergoes  an  analogous  change. 
Its  caseine  is  liquefied,  while  its  liberated  fat  globules  rise  to  the  upper 
part  of  the  fluid,  forming  a  creamy-looking  layer  on  its  surface. 

Adipose  tissue  is  disintegrated  by  the  liquefaction  of  its  fibrous  and 
membranous  parts,  while  the  fatty  matter  escapes  in  the  form  of  oil 
drops,  floating  upon  the  other  contents  of  the  stomach.  Beaumont 
always  found  free  oil  globules,  thus  extricated  from  the  fatty  tissues 
soon  after  they  had  been  taken  with  the  food ;  and  it  is  easy  to  verify 
this  observation,  either  by  artificial  digestion  of  adipose  tissue  in 
gastric  juice,  or  by  opening  the  stomach  of  an  animal  after  the  admin- 
istration of  food  containing  fat. 

The  digestion  of  muscular  flesh  is  also  at  first  a  process  of  disin- 
tegration. The  connective  tissue  surrounding  the  fibrous  bundles 
yields  to  the  action  of  the  gastric  juice,  and  the  fibres  become  sepa- 
rated, forming  a  gruelly  mixture  of  microscopic  threads  and  fragments. 
The  fibres  then  break  up,  and,  when  examined  by  the  microscope,  are 
found  to  have  lost  the  distinctness  of  their  transverse  striations.  In 
food  which  has  been  thoroughly  masticated,  this  change  goes  on  rap- 
idly and  uniformly  throughout  the  mass.  If,  as  in  the  dog,  the  meat 
be  swallowed  without  much  mastication,  or  if  portions  be  suspended 
in  a  test-tube  with  gastric  juice,  the  digestive  action  progresses  from 
without  inward.  The  external  parts  are  first  softened  and  decolorized, 
becoming  covered  with  a  grayish  layer,  of  grumous  consistency,  con- 
taining the  isolated  fragments  of  muscular  fibre.  As  these  portions 
are  removed,  the  action  extends  to  the  parts  beneath,  and  so  on  until 


164  FUNCTIONS    OF    NUTRITION. 

the  whole  is  reduced  to  a  uniform  mixture,  of  gruelly  consistency,  in 
which  only  remnants  of  the  muscular  fibres  can  be  detected  by  the 
microscope.  It  is  this  apparently  homogeneous,  pultaceous,  or  semi-fluid 
material  that  was  formerly  designated  by  the  name  of  "  chyme."  It  is 
a  mixture  of  disintegrated  and  semi-digested  tissues,  portions  of  which 
have  been  liquefied  while  others  are  not  yet  reduced  to  a  state  of 
solution. 

Milk,  when  taken  into  the  stomach  in  a  fresh  condition,  is  first  coagu- 
lated, afterward  dissolved.  The  preliminary  coagulation  of  its  caseine, 
under  the  influence  of  the  gastric  juice,  takes  place  very  rapidly. 
Beaumont  found  that  milk  could  be  withdrawn  in  a  coagulated  condi- 
tion fifteen  minutes  after  its  introduction  into  the  stomach ;  and  that 
if  the  mixture  were  kept  at  the  temperature  of  38°  C.,  the  coagula  were 
again  liquefied  in  the  course  of  eight  hours.  The  coagulation  of  milk, 
by  contact  with  the  gastric  juice,  is  in  the  form  of  minute,  soft  flocculi, 
which,  at  the  temperature  of  the  body,  readily  undergo  the  conversion 
into  peptone,  and  are  thus  redissolved.  Milk,  as  used  by  adults,  in 
various  culinary  preparations,  is  generally  incorporated,  in  the  coagu- 
lated form,  with  other  articles  of  food. 

The  vegetable  tissues,  as  a  rule,  are  digested  in  a  manner  similar  to 
that  described  above.  The  albuminous  matters  are  dissolved  out,  leav- 
ing the  starchy  and  oleaginous  ingredients  in  a  free  condition,  but  chemi- 
cally unchanged.  As  these  tissues  generally  contain  a  smaller  propor- 
tion of  albuminous  matter  than  animal  food,  the  main  result  of  the 
changes  which  they  undergo  in  the  stomach  is  their  disintegration. 

The  gastric  juice,  after  commencing  its  action  in  the  stomach,  passes, 
with  the  debris  of  the  food,  into  the  intestine.  This  can  be  seen  in  the 
dog  by  killing  the  animal  after  feeding,  and  examining  the  contents  of 
the  alimentary  canal.  The  same  thing  may  be  observed  by  means  of 
a  duodenal  fistula,  established  by  an  operation  similar  to  that  for  fistula 
of  the  stomach.  A  silver  tube,  with  flanges  at  each  end,  is  introduced 
into  the  lower  part  of  the  duodenum,  and  the  wound  allowed  to  heal, 
after  which  the  contents  of  the  intestine  may  be  withdrawn  and  exam- 
ined at  different  periods  of  digestion. 

About  half  an  hour  after  the  ingestion  of  a  meal,  the  gastric  juice 
begins  to  pass  into  the  duodenum,  recognizable  by  its  strongly-marked 
acidity,  and  containing  a  certain  quantity  of  peptone  in  solution.  It 
soon  afterward  becomes  mingled  with  the  debris  of  muscular  fibres,  fat 
vesicles,  and  oil  drops ;  substances  easily  recognizable  under  the  micro- 
scope, and  which  produce  a  grayish  turbidity  in  the  fluid  withdrawn 
from  the  fistula.  By  the  continuous  passage,  in  this  way,  of  alimen- 
tary material,  mixed  with  gastric  juice,  the  stomach  becomes  gradually 
cleared  of  its  contents.  In  the  experiments  of  Beaumont  the  time 
required  for  the  disappearance  of  food  from  the  stomach  varied  from 
one  hour  to  five  hours  and  a  half,  according  to  the  quality  ami  quantity 
of  the  material  used.  In  those  of  Prof.  F.  G.  Smith  on  the  same  sub- 
ject, food  seldom  remained  in  the  stomach  more  than  two  hours  after  its 


DIGESTION.  165 

introduction.  Three  hours  is  probably  sufficient,  as  a  rule,  for  complete 
stomach  digestion,  in  man,  when  the  food  is  in  moderate  quantity  and  has 
been  properly  prepared  by  cooking  and  mastication.  In  the  dog,  where 
the  food  is  generally  swallowed  in  fragments  of  some  size,  the  process  is 
longer ;  and  a  moderate  meal  of  fresh  uncooked  meat  requires  from  nine 
to  twelve  hours  for  its  liquefaction  and  disappearance  from  the  stomach. 

The  gastric  juice,  after  accomplishing  its  work  in  digestion,  is  reab- 
sorbed  from  the  alimentary  canal  by  the  blood-vessels.  It  forms  a 
vehicle  for  the  dissolved  nutritious  material,  and  again  enters  the 
circulation,  bringing  with  it  the  alimentary  substances  in  solution. 
An  abundant  supply  of  the  secretion  may  therefore  be  poured  out 
during  digestion,  at  an  expense  to  the  blood,  at  any  one  time,  of  only 
a  small  quantity  of  fluid.  The  simplest  investigation  shows  that  neither 
gastric  juice  nor  peptones  accumulate  to  any  considerable  amount  in  the 
stomach ;  each  portion  of  the  food,  when  digested,  being  disposed  of  by 
absorption,  together  with  its  solvent  fluid.  There  must  be  accordingly, 
during  digestion,  a  continuous  circulation  of  fluids  from  the  blood-ves- 
sels to  the  alimentary  canal,  and  from  the  alimentary  canal  back  again 
to  the  blood-vessels. 

That  this  really  takes  place  is  shown  by  the  following  facts :  First, 
if  a  dog  be  killed  some  hours  after  feeding,  there  is  never  more  than  a 
very  small  quantity  of  fluid  found  in  the  stomach,  just  sufficient  to 
smear  over  and  penetrate  the  half  digested  pieces  of  meat;  and  sec- 
ondly, in  the  living  animal,  gastric  juice,  drawn  from  the  fistula  five 
or  six  hours  after  digestion  has  been  going  on,  contains  little  or  no  more 
peptone  in  solution  than  that  extracted  fifteen  or  twenty  minutes  after 
the  introduction  of  food.  To  obtain  gastric  juice  saturated  with  ali- 
mentary matter,  it  must  be  artificially  digested  with  food  in  test-tubes, 
where  absorption  and  renovation  cannot  take  place. 

The  secretion  of  gastric  juice  is  much  influenced  by  nervous  condi- 
tions. It  was  noticed  by  Beaumont,  in  his  experiments  with  St.  Mar- 
tin, that  irritation  of  the  temper  or  other  moral  causes  would  often 
diminish  or  suspend  the  supply  of  the  gastric  fluids.  Any  febrile 
action  or  unusual  fatigue  would  exert  a  similar  effect.  Every  one  is 
aware  how  readily  mental  disturbances,  such  as  anxiety,  anger,  or  vexa- 
tion, will  take  away  the  appetite  and  interfere  with  digestion.  Impres- 
sions of  this  kind,  especially  at  the  commencement  of  the  process,  seem 
liable  to  produce  a  lasting  effect  and  to  disturb  digestion  for  the  entire 
day.  In  order,  therefore,  that  the  function  may  be  properly  performed, 
food  should  be  taken  only  when  the  appetite  demands  it ;  it  should  be 
thoroughly  masticated ;  and,  finally,  both  mind  and  body,  particularly 
in  the  early  part  of  digestion,  should  be  free  from  unusual  or  dis- 
agreeable excitement. 

Pancreatic  Juice. 

The  pancreas,  which  is  similar  in  general  structure  to  the  salivary 
glands,  lies  across  the  upper  part  of  the  abdomen,  with  its  larger  or 


166  FUNCTIONS    OF    NUTRITION. 

right-hand  extremity  in  contact  with  the  duodenum.  It  is  traversed 
longitudinally  by  a  main  excretory  duct,  receiving-,  as  it  passes  from  left 
to  right,  lateral  branches  from  the  glandular  lobules,  and  opening  into 
the  duodenum  next  to  the  orifice  of  the  common  biliary  duct,  about  ten 
centimetres  below  the  pylorus.  Its  secretion  thus  mingles  with  the 
products  of  stomach  digestion,  almost  immediately  after  they  have 
passed  into  the  duodenum. 

FIG.  25. 


PORTION  or  HUMAN  PANCREAS  AND  DUODENUM.— a.  Cavity  of  duodenum.    6.  Orifice  of  the  pan- 
creatic duct.    c.  Orifice  of  lower  pancreatic  duct.    (Bernard.) 

The  arrangement  of  the  gland  and  its  duct,  in  the  lower  animals,  is 
in  most  respects  similar  to  the  above.  In  the  dog  and  cat,  there  are 
two  ducts  opening  into  the  intestine,  one  in  juxtaposition  with  the 
biliary  duct,  the  other  from  one  to  three  centimetres  farther  down. 
The  lower  duct  is  usually  in  these  animals,  though  not  always,  the 
larger  of  the  two,  and  they  generally  communicate  with  each  other  in 
the  substance  of  the  gland  by  a  transverse  branch.  Even  in  man,  as 
shown  by  Bernard,  Kolliker,  and  Sappcy  (Fig.  25),  there  is  often  a 
small  accessory  duct  opening  into  the  intestine,  sometimes  above  and 
sometimes  below  the  principal  excretory  orifice.  The  most  marked  pe- 
culiarity of  these  parts  is  in  the  rabbit,  where  the  single  pancreatic  duct 
opens  into  the  intestine  30  or  40  centimetres  below  the  biliary  duct. 

The  pancreatic  juice  is  obtained  from  the  living  animal  by  opening 
tl.e  abdomen,  and  inserting  a  canula  into  the  main  pancreatic  duct, 
immediately  before  its  entrance  into  the  intestine.  The  canula  being 
secured  in  position  by  a  ligature  placed  around  the  duct,  the  parts  are 
returned  to  the  abdominal  cavity,  the  external  wound  closed  with 


DIGESTION.  167 

sutures,  and  the  extremity  of  the  canula  left  projecting  between  its 
edges.  The  secretion  is  thus  diverted  from  the  intestine,  and  may  be 
collected  as  it  flows  from  the  canula.  The  operation  has  been  most 
frequently  performed  on  the  dog,  but  it  has  also  been  done  on  the 
rabbit,  the  ox,  the  sheep,  the  goat,  the  pig,  and  the  goose.  The  secre- 
tion has  been  obtained  from  the  horse,  by  opening  the  duodenum  and 
inserting  a  canula  in  the  orifice  of  the  pancreatic  duct. 

The  fistula  produced  by  this  means  is  a  temporary  one,  as  the  ligature 
soon  cuts  its  way  through  the  duct,  and  the  canula  is  displaced ;  the 
communication  of  the  duct  with  the  intestine  soon  becoming  re-estab- 
lished. In  the  ox,  this  happens  within  six  or  eight  days  after  the 
operation ;  and  in  the  dog,  according  to  Bernard,  within  three  days. 
As  the  pancreas,  furthermore,  is  very  sensitive  to  irritation  and  its 
secretion  liable  to  alteration  by  the  inflammatory  process,  it  should  be 
collected  for  examination  within  twenty-four  hours  after  the  insertion 
of  the  canula. 

Physical  Properties  and  Composition  of  the  Pancreatic  Juice. — 
Pancreatic  juice,  obtained  from  the  dog  in  the  above  manner,  during 
digestion,  is  a  clear,  colorless  fluid,  distinctly  alkaline,  with  a  well 
marked  viscid  consistency,  like  fluid  white  of  egg.  Owing  to  the 
abundance  of  its  albumenoid  ingredients,  it  coagulates  completely  at 
the  boiling  temperature,  often  solidifying  into  a  jelly-like  mass.  It  also 
assumes  a  gelatinous  consistency  on  being  cooled  down  to  0°  C.,  again 
liquefying  when  raised  to  the  ordinary  temperature.  According  to 
Schmidt,*  it  has  the  following  composition: 

COMPOSITION  OF  PANCREATIC  JUICE. 

Water 900.76 

Alburn enoid  substances 90.44 

Sodium  chloride 7.35 

Potassium  chloride        .......  0.02 

Lime  phosphate 0.41 

Magnesian  phosphate     .......  0.12 

Soda,  lime,  and  magnesia,  in  organic  combination        .  0.90 

1000.00 

The  pancreatic  juice  resembles  a  solution  of  albumen  in  being  coag- 
ulable  by  heat,  by  mineral  acids,  and  by  alcohol  in  excess.  It  presents, 
however,  the  important  distinction  that  its  organic  matter,  after  being 
precipitated  by  alcohol,  is  again  soluble  in  water.  This  substance  is, 
therefore,  different  in  character  from  ordinary  albumen,  notwithstand- 
ing the  similarity  in  some  of  its  reactions. 

A  striking  peculiarity  of  this  secretion,  due  to  the  presence  of  its 
albumenoid  matter,  is  its  property  of  emulsioning  neutral  fats.  If  a 
few  drops  of  oil  be  shaken  in  a  test-tube  with  fresh  pancreatic  juice,  it 
is  instantaneously  broken  up  into  a  permanent  uniform  emulsion ;  and 
if  the  oil  be  in  slight  excess  it  forms,  after  a  time,  an  opaque  creamy 
layer  upon  the  surface,  the  greater  part  remaining  diifused  through  the 

*  Annalen  der  Chemie  und  Pharmacie.     Heidelberg,  1854,  Band  xcii.,  p.  33. 


168  FUNCTIONS    OF    NUTRITION. 

mixture.  The  pancreatic  juice  acts  in  this  way  like  a  solution  of 
albumen.  Its  emulsifying  power  is  not  due  to  its  alkaline  reaction,  but 
to  the  organic  matter  which  it  contains ;  since  its  alkalescence  may  be 
neutralized,  as  shown  by  Bernard,*  without  sensibly  impairing  its 
activity  in  this  respect.  The  instantaneous  effect  thus  produced  on 
the  fats  is  limited  to  their  emulsion.  They  are  disseminated  through 
the  fluid  in  the  form  of  minute  particles,  but  their  chemical  characters 
are  not  altered  until  other  changes  occur  at  a  later  time. 

Among  the  albumenoid  ingredients  of  the  pancreatic  juice  are 
substances  belonging  to  the  class  of  ferments,  which  exert  three 
distinct  actions  on  alimentary  substances;  namely,  a  transforming 
action  on  starch,  a  digestive  action  on  coagulated  albumen,  and  a  partial 
acidifying  action  on  fats.  All  these  substances  may  be  precipitated  by 
alcohol  from  pancreatic  juice,  or  extracted  by  water  or  by  glycerine 
from  the  pancreatic  tissue ;  but  they  have  not  been  obtained  in  a  state 
of  purity,  or  even  distinctly  separated  from  each  other,  to  the  satis- 
faction of  physiological  chemists. 

The  first  of  these  substances,  the  so-called  pancreatine,  is  a  diastatic 
ferment ;  that  is,  it  has  the  power,  like  vegetable  diastase,  of  trans- 
forming starch  into  glucose.  It  produces  this  change  very  readily  at 
the  temperature  of  the  body,  and  it  may  be  preserved  under  alcohol  or 
in  glycerine  for  an  indefinite  time  without  losing  its  properties.  When 
dry,  it  may  be  heated  to  100°  C.,  and  still  retain  its  catalytic  power ; 
but  in  watery  solution,  it  is  coagulated  and  rendered  inactive  by  a  boil- 
ing temperature.  It  is  produced  in  the  gland,  probably  by  the  trans- 
formation of  some  previously  formed  substance,  since  it  has  been  found 
by  Liversidge,f  that  after  it  has  been  completely  extracted  by  glycerine 
from  the  chopped  glandular  tissue,  the  inactive  residue,  if  exposed  to 
the  air  for  five  or  six  hours,  will  regenerate  the  ferment,  so  that  it  may 
again  be  extracted  by  water  or  glycerine.  This  ferment  exists  in  the 
pancreas  and  the  pancreatic  juice  of  every  animal  thus  far  examined. 
The  second  ferment,  known  as  trypsine,  is  that  which  causes  the  solu- 
tion of  albumenoid  matters.  This  property  of  the  pancreatic  juice,  first 
observed  by  Bernard  and  Corvisart,  has  been  the  subject  of  many  exper- 
iments, among  the  most  valuable  of  which  are  those  of  Kiihne.J  This 
observer  operated  both  with  the  pancreatic  juice  of  the  dog  and  with 
infusions  of  the  glandular  tissue.  He  found  that  the  fresh  viscid 
secretion  could,  in  from  half  an  hour  to  three  hours,  effect  the  solution 
of  coagulated  fibrine  and  albumen,  without  modification  of  its  alkaline 
reaction.  If  the  process  be  arrested  at  this  point  no  putrefactive 
changes  take  place  in  it ;  but  if  continued  for  a  longer  time,  it  gives 
rise  to  the  products  of  decomposition.  The  activity  of  this  ferment  is 
greatest  in  an  alkaline  solution ;  it  goes  on,  though  with  less  energy, 

*  Liquides  de  POrganisme.     Paris,  1859,  tome  ii.,  p.  346. 

f  Studies  from  the  Physiological  Laboratory  of  the  University  of  Cambridge, 
Part  I.  Cambridge,  1873,  p.  49. 

$  Archiv  fur  puthologische  Anatomic  und  Physiologic,  1867,  xxxix.,  p.  130. 


DIGESTION.  169 

in  a  neutral  mixture ;  and  is  nearly  or  quite  suspended  in  the  presence 
of  a  dilute  acid.  Under  favorable  conditions  it  dissolves  not  only  coag- 
ulated fibrine  and  albumen,  but  also  the  substance  of  animal  tissues. 
In  his  experiments  with  the  tissue  of  the  pancreas,  Kiihne  placed  the 
finely  divided  gland  in  warm  water,  with  a  weighed  quantity  of  the 
substance  to  be  experimented  on  ;  allowing  the  infusion  of  the  pancreas 
and  the  digestion  of  the  albuminous  matter  to  proceed  simultaneously. 
He  found  that  when  employing  for  this  purpose  a  dog's  pancreas  of 
from  50  to  60  grammes  weight,  400  grammes  of  boiled  and  pressed 
fibrine  were  reduced  to  an  insignificant  residue  in  from  three  to  six 
hours,  the  reaction  of  the  mass  continuing  faintly  alkaline. 

The  action  of  the  pancreatic  ferment  on  albumenoid  matters  differs 
from  that  of  pepsine  in  its  details,  but  is  the  same  in  its  result.  If 
coagulated  fibrine  be  immersed  in  pancreatic  juice  or  an  alkaline  *ryp- 
sine  solution,  it  does  not  become  swollen  and  gelatinized,  nor  is  it 
transformed  into  syntonine  as  it  would  be  in  gastric  juice.  The  pieces 
of  fibrine  become  rather  shrivelled  and  condensed,  and  are  afterward 
liquefied  without  passing  through  the  modification  of  syntonine.  But 
when  liquefaction  is  accomplished,  the  substance  in  solution  has  all  the 
characters  of  peptone,  in  the  same  degree  as  if  produced  by  stomach 
digestion — its  non-coagulability  by  heat,  its  solubility  in  water,  in  dilute 
acids  and  alkalies,  and  in  neutral  solutions,  and  its  diffusibility  through 
animal  membranes.  The  final  change  produced  by  trypsine  in  albu- 
menoid substances  appears,  therefore,  to  be  a  hydration,  but  effected  by 
a  different  process  from  that  of  digestion  with  gastric  juice. 

It  seems  evident,  accordingly,  that  the  pancreas  during  life  produces 
a  ferment  which  is  capable  of  dissolving  its  own  tissue.  The  difficulty 
of  accounting  for  such  a  fact  is  greater  in  this  case  than  in  that  of  the 
stomach ;  since  the  pancreatic  ferment  is  most  active  in  presence  of  an 
alkaline  reaction,  like  that  of  the  blood  and  the  interstitial  fluids  of  the 
tissues.  It  is  indicated  by  the  experiments  of  Haidenhain  that  trypsine 
is  not  contained  under  its  own  form  in  the  glandular  cells  during  life, 
but  is  produced,  at  the  moment  of  secretion  or  after  death,  from  a  pre- 
existing inactive  substance,  termed  "zymogen."  There  are,  no  doubt, 
such  preliminary  stages  in  the  formation  of  all  ferment  bodies ;  but  the 
trypsine  ferment  is  actively  present  in  freshly  secreted  pancreatic  juice, 
and  its  mode  of  production  from  the  preceding  inert  material  must  be 
for  the  most  part  a  matter  of  surmise.  The  pancreas  does  not  appear 
liable,  like  the  stomach,  to  self-digestion  after  death,  though  the  sur- 
rounding conditions  would  seem  often  favorable  to  such  an  alteration. 

The  third  substance  of  this  kind  in  the  pancreatic  juice,  causing 
decomposition  of  the  neutral  fats,  with  liberation  of  a  fatty  acid,  has 
not  received  a  distinct  name.  It  is  known,  however,  by  its  action 
whenever  fresh  pancreatic  juice,  an  infusion  of  the  pancreas,  or  its 
moist  tissue,  is  brought  in  contact  with  liquid  neutral  fat  at  the  temper- 
ature of  35°  to  40°  C.  In  a  short  time  an  acid  reaction  becomes 
manifest,  sufficient  to  redden  blue  litmus-paper,  and  on  keeping  the 


170  FUNCTIONS    OF    NUTRITION. 

mixture  at  the  above  temperature,  the  quantity  of  acid  increases. 
Bernard  and  Bertelot*  have  shown  that  in  this  process  the  fat  is  decom- 
posed into  a  fatty  acid  and  glycerine.  A  few  decigrammes  of  neutral 
fat,  emulsified  with  20  grammes  of  fresh  pancreatic  juice  from  the  dog, 
and  kept  at  a  moderately  warm  temperature,  were  almost  completely 
acidified  at  the  end  of  twenty-four  hours,  leaving  only  about  one-tenth 
part  of  undecomposed  fat.  The  change  which  occurs  when  fat  is  re- 
placed by  a  fatty  acid  and  glycerine,  is  as  follows : 

Stearine.  Water.         Stearic  Acid.    Glycerine. 

C67  Hm  06  +  3  (Ha  O)  =  CH  H108  06  +  C3 II,  03 

It  includes,  therefore,  a  hydration,  and  cannot  take  place  except  in  the 
presence  of  water.  If  the  experiment  be  performed  with  pancreatic 
juice  of  normal  alkaline  reaction,  or  with  alkaline  infusions  of  the 
pancreas,  a  portion  of  the  acid  set  free  is  saponified  by  union  with  the 
alkaline  bases.  The  chemical  change  accordingly  is  the  same  as  that 
in  the  saponification  of  fats  by  continued  boiling  with  water  and  an 
alkali;  the  ferment  of  the  pancreatic  juice,  in  a  short  time  and  at  a 
moderate  warmth,  taking  the  place  of  prolonged  ebullition  in  its  influ- 
ence an  the  fats. 

According  to  Wurtz  and  Hoppe-Seyler,  this  ferment,  unlike  the  two 
preceding,  is  insoluble  in  glycerine,  and  is  rendered  inactive  by  contact 
with  alcohol.  Its  action  can  be  studied  only  in  the  pancreatic  juice, 
or  in  watery  infusions  of  the  glandular  tissue ;  and  its  physical  dual- 
ities and  composition  arc  even  more  imperfectly  understood  than  those 
of  other  bodies  of  the  same  class. 

Mode  of  Secretion  and  Daily  Quantity  of  the  Pancreatic  Juice.— 
When  examined  in  the  living  animal  by  means  of  a  canula  introduced 
into  its  excretory  duct,  it  is  found  that  the  action  of  the  pancreas 
varies  much  in  activity  at  different  times.  In  the  intervals  of  diges- 
tion, or  if  the  process  be  temporarily  arrested  from  any  cause,  no  fluid 
whatever  is  discharged  from  the  cauula.  When  digestion  is  in  progress, 
the  pancreatic  juice  soon  begins  to  run  from  the  orifice  of  the  tube,  at 
first  slowly  and  in  drops.  Sometimes  the  drops  follow  each  other  with 
rapidity  for  a  few  moments,  after  which  the  discharge  is  suspended. 
It  then  recommences,  and  continues  to  exhibit  similar  fluctuations  dur- 
ing the  whole  course  of  the  experiment.  Its  flow,  however,  is  at  all 
times  scanty,  as  compared  with  that  of  the  gastric  juice.  Wo  have 
never  been  able  to  collect,  in  a  dog  of  medium  size,  more  than  75 
grammes  in  three  hours,  and  usually  the  quantity  has  been  much  less 
than  this.  Colin  found  a  great  variation  in  the  animals  on  which  he 
experimented,  the  quantity  being  from  two  and  a  half  to  thirty  times 
as  abundant  at  oru1  period  as  at  another.  In  the  bullock,  while  rumi- 
nating, the  largest  quantity  obtained  was  ;M:>  grammes  per  hour. 

The  entire  quantity  of  pancreatic  juice  per  day  cannot  thrivi'mv  In- 
determined  with  precision,  but  it  is  evidently  moderate  in  amount,  as 

lU-rnurd,  Lrrons  dc  1'hysiologie  Exp&imcntale.     Paris,  1856,  p.  263. 


DIGESTION.  171 

compared  with  the  other  digestive  fluids.  In  the  ox,  cow,  and  horse, 
Colin  found  the  average  quantity  nearly  the  same,  corresponding  to 
about  0.58  gramme  per  hour  for  every  kilogramme  of  bodily  weight. 
Schmidt  found  it,  in  the  dog,  not  more  than  0.2  gramme  per  kilogramme 
per  hour.  In  the  most  successful  instances,  we  have  found  it,  in  the 
dog,  as  much  as  1.25  gramme  per  kilogramme  per  hour  during  diges- 
tion, but  much  less  than  this  in  the  intervals.  If  we  take,  as  the 
average  of  these  estimates,  0.5  gramme  per  hour  for  every  kilo- 
gramme of  bodily  weight,  it  would  give  for  a  man  of  medium  size 
about  800  grammes  as  the  entire  quantity  secreted  per  day. 

The  condition  of  the  pancreas  varies  at  different  periods  correspond- 
ing with  the  activity  of  its  secretion.  In  the  intervals  of  digestion  it 
is  pallid  and  dense ;  during  digestion  it  becomes  turgid  and  vascular, 
its  ruddy  color  showing  the  increased  quantity  of  blood  in  its  vessels. 
According  to  most  observers,  the  ferment  which  effects  the  solution  of 
albuminous  matters  can  only  be  extracted  from  the  pancreas  of  animals 
killed  during  the  height  of  digestive  action,  which,  in  the  dog,  is  from 
five  to  seven  hours  after  the  ingestion  of  food.  When  digestion  comes 
to  an  end,  the  vascularity  of  the  pancreas  diminishes,  and  the  organ 
returns  to  its  quiescent  condition.  This  periodical  excitement  at  the 
time  of  functional  activity  is  observable,  not  only  in  the  pancreas,  but 
in  all  parts  of  the  digestive  apparatus. 

Physiological  Action  of  the  Pancreatic  Juice — Among  the  most 
important  effects  produced  by  pancreatic  juice  in  digestion  is  the  emul- 
sification  of  the  fats.  This  action  is  prompt  and  efficient  when  oil 
is  mixed  with  pancreatic  juice  in  a  test-tube,  quite  unlike  anything 
obtained  by  similar  experiments  with  saliva,  gastric  juice,  or  bile. 
Bernard  found  that  the  fresh  pancreatic  juice  of  the  dog,  at  38°  C., 
would  form  a  complete  and  permanent  emulsion  with  olive  oil,  butter, 
suet,  or  lard,  when  mixed  with  either  of  these  substances  in  the  pro- 
portion of  one  gramme  of  oleaginous  matter  to  two  grammes  of 
pancreatic  juice.  In  the  horse,  ass,  ox,  sheep,  and  pig,  according  to 
Colin,*  this  property  of  the  pancreatic  juice  is  in  proportion  to  the 
amount  of  its  albumenoid  matter ;  one  part  of  oil  requiring  for  com- 
plete emulsion  from  two  to  three  parts  of  pancreatic  juice  when  its 
organic  ingredients  are  abundant,  and  four,  five,  or  six  parts  when  they 
are  in  smaller  quantity. 

Within  the  alimentary  canal  the  emulsive  action  of  the  pancreatic 
juice  is  equally  well  marked.  The  fats  are  not  affected  by  either  saliva 
or  gastric  juice ;  and  examination  shows  that  they  are  unchanged  in 
their  essential  characters  so  long  as  they  remain  in  the  stomach.  In 
this  organ  they  are  simply  liquefied  by  the  warmth  of  the  body,  and 
set  free  by  the  solution  of  their  albuminous  envelopes ;  and  they  are 
still  visible  in  larger  or  smaller  drops  on  the  surface  of  the  alimentary 
mass.  But  almost  immediately  after  passing  into  the  intestine,  the 

*  Physiologie  Comparee  des  Animaux  domestiques.     Paris,  1854,  tome  i.,  p.  644. 


172  FUNCTIONS    OF    NUTRITION. 

oily  portion  of  the  food  is  altered  in  appearance,  being  converted  into 
a  white,  opaque  emulsion,  termed  chyle,  always  found  during  digestion 
entangled  among  the  valvulae  conniventes,  and  adhering  to  the  surface 
of  the  small  intestine.  The  digestion  of  fatty  substances  consists 
mainly  in  this  emulsion,  by  which  they  are  converted  into  chyle  and 
made  ready  for  absorption.  As  the  change  begins  to  take  place  in  the 
duodenum,  immediately  below  the  orifice  of  the  pancreatic  duct,  this 
circumstance  points  to  the  pancreatic  juice  as  the  main  agent  in  the 
formation  of  chyle.  But  in  most  animals  the  biliary  duct  opens  into 
the  intestine  at  nearly  the  same  point,  and  it  might  therefore  be 
questioned  whether  the  bile  has  not  an  equal  share  in  the  result.  This 
doubt  was  removed  by  the  experiments  of  Bernard  on  the  rabbit.  In 
this  animal,  the  biliary  duct  opens,  in  the  usual  manner,  just  below 
the  pylorus,  while  the  pancreatic  duct  communicates  with  the  intestine 
30  or  40  centimetres  farther  down ;  so  that  there  is  a  considerable 
extent  of  the  small  intestine  containing  bile,  into  which  the  pancreatic 
juice  has  not  yet  been  discharged.  Bernard  fed  these  animals  with 
substances  containing  oil,  or  injected  melted  butter  into  the  stomach; 
and,  on  killing  them  afterward,  found  no  chyle  in  the  intestine 
between  the  openings  of  the  biliary  and  pancreatic  ducts,  while  it 
was  abundant  immediately  below  the  orifice  of  the  latter.  Above 
this  point  the  lacteal  vessels  were  empty  or  transparent,  while  below 
it  they  were  full  of  opaque  chyle.  These  experiments,  which  were 
confirmed  by  Jackson,*  show  that  the  emulsifying  action  of  the 
pancreatic  juice  on  oily  matters  is  exerted  within  the  body  during 
digestion,  and  that  it  is  the  direct  agent  in  the  production  of  chyle  in 
the  intestine. 

It  is  probable  that  the  acidifying  action  of  pancreatic  juice  on  fats 
is  less  extensive  during  digestion  than  its  emulsive  effect.  These  two 
properties  of  the  secretion,  when  examined  in  the  test-tube,  show  a  dif- 
ference in  their  mode  of  action.  The  emulsification  of  fat,  when  in  contact 
with  pancreatic  juice,  is  instantaneous  and  complete;  but  its  acidifi- 
cation requires  a  longer  time,  and  increases  progressively  for  some 
hours.  A  partial  acidification  and  saponification  undoubtedly  takes 
place  in  the  duodenum  ;  but  the  greater  part  of  the  fat  remains  in  the 
form  of  an  emulsion,  and  the  absorption  of  chyle  begins  immediately 
below  the  orifice  of  the  pancreatic  duct,  as  shown  by  the  condition  of 
the  lacteal  vessels.  The  chyle  in  the  lacteal  vessels  is  mainly  com- 
posed of  undecomposed  fat;  and,  according  to  Hoppe-Seyler,  the  quan- 
tity of  saponified  fat,  in  both  the  intestine  and  the  lacteals,  is  compara- 
tively insignificant. 

The  second  important  action  of  the  pancreatic  juice  in  digestion  is 
the  transformation  of  starch  into  glucose.  It  is  much  more  effective 
in  this  respect  than  the  saliva,  being  almost  instantaneous,  and  con- 
verting the  whole  of  the  starch  at  once,  while  that  of  the  saliva  is 


*  American  Journal  of  the  Medical  Sciences.     Philadelphia,  October,  1854. 


DIGESTION.  173 

gradual  and  leaves  for  some  time  a  part  of  the  starch  unchanged. 
Kroeger  found  that  one  gramme  of  fresh  pancreatic  juice,  at  the  tem- 
perature of  35°  C.,  transformed  into  glucose,  within  thirty  minutes, 
4.67.  grammes  of  starch;  while,  according  to  our  own  observations, 
one  gramme  of  fresh  human  saliva,  mixed  at  38°  C.  with  a  watery 
solution  containing  less  than  0.1  gramme  of  boiled  starch,  though  it 
gives  a  manifest  sugar  reaction  in  one  minute,  still  contains  a  large 
portion  of  unaltered  starch  at  the  end  of  an  hour.  According  to 
various  observers  (Bouchardat  and  Sandras,  Ranke,  Gorup-Besanez), 
pancreatic  juice  also  causes  the  transformation  of  raw  starch,  a  prop- 
erty which  was  found  by  Bouchardat  to  be  very  energetic  in  the 
secretion  of  the  common  fowl. 

Starch  which  has  passed  the  stomach  unchanged  is  thus  promptly 
transformed  into  glucose  after  entering  the  duodenum.  In  dogs,  fed 
with  a  mixture  of  meat  and  boiled  starch,  and  killed  at  various  periods 
after  feeding,  starch  is  for  a  time  abundantly  recognizable  in  the  stomach 
without  traces  of  glucose,  while  in  the  fluids  of  the  small  intestine  it 
is  absent  and  glucose  takes  its  place.  According  to  Langendorff,* 
exclusion  of  the  pancreatic  juice  from  the  intestine  in  pigeons  arrests 
so  completely  the  digestion  and  assimilation  of  starch,  that  these 
animals  die  after  considerable  emaciation,  in  from  six  to  twelve  days. 
This  secretion  is  plainly  the  principal  agent  in  the  digestion  of  starch, 
and  as  starchy  substances  constitute,  in  man,  rather  more  than  one-half 
the  entire  food,  its  function  is  hardly  second  in  importance  to  any  other 
in  the  alimentary  canal. 

It  is  less  easy  to  judge  of  the  pancreatic  juice,  as  an  agent  in  the 
solution  of  albuminous  matters.  Some  writers  attribute  much  impor- 
tance to  this  action,  owing  to  its  striking  character  in  artificial  diges- 
tions. But  it  is  hardly  safe  to  assume  that  these  experiments  represent 
fully  the  phenomena  of  intestinal  digestion.  In  the  alimentary  canal 
a  number  of  different  secretions  are  in  operation  together  or  succes- 
sively, and  the  properties  of  each  may  be  more  or  less  modified  by  the 
time  of  its  secretion,  or  the  proportion  in  which  it  is  mingled  with  the 
others.  The  action  of  pancreatic  juice  on  albumenoids  is  most  marked 
in  an  alkaline  menstruum,  and  is  diminished  or  arrested  by  an  acidity 
less  than  that  of  the  gastric  juice.  But  the  reaction  of  the  small 
intestine  in  carnivorous  animals,  during  digestion,  is  acid.  According 
to  Bernardf  this  is  always  the  case.  In  our  own  experiments,  with  a 
duodenal  fistula  in  the  dog,  the  fluids  of  the  intestine  became  acid  as 
soon  as  the  contents  of  the  stomach  began  to  pass  the  pylorus.  Accord- 
ing to  Schmidt-Mulheim,|  who  operated  by  killing  the  animals  at 
various  periods  after  feeding  and  examining  the  intestinal  contents, 
the  reaction  of  the  dog's  small  intestine  during  the  digestion  of  meat 


*  Archly  fur  Anatomic  und  Physiologic.     Leipzig,  1879,  p.  26. 

f  Liquides  de  1'Organisme.     Paris,  1859,  tome  ii.,  p.  347. 

%  Archiv  fur  Anatomie  und  Physiologic.     Leipzig,  1879,  p.  39. 


174  FUNCTIONS    OF    NUTRITION. 

is  always  acid,  usually  even  to  its  lowest  portions.  Moreover,  some 
of  the  products  of  artificial  digestion  do  not  occur  with  the  same  readi- 
ness in  the  intestine  of  the  living  animal.  In  Kiihne's  experiments  on 
the  artificial  digestion  of  coagulated  fibrine  by  trypsine  solutions,  about 
one-half  the  peptone  produced  was  further  decomposed  into  other  pro- 
ducts, especially  leucine  and  tyrosine.  In  the  observations  of  Schmidt- 
Mulheim,  on  the  contrary,  the  acid  contents  of  the  small  intestine  in 
dogs,  during  the  digestion  of  meat,  were  very  poor  in  leucine  and  tyro- 
sine,  but  abundant  in  peptone.  He  concludes  that  the  digestion  of 
albumen  is  almost  wholly  performed  by  the  pepsine  ferment  in  an  acid 
menstruum,  that  is,  by  the  gastric  juice  ;  and  that  the  office  of  the 
pancreatic  juice  in  this  respect  is  secondary. 

Bile. 

As  compared  with  other  accessory  glands  of  the  alimentary  canal, 
the  liver  presents  several  striking  peculiarities.  First,  its  supply  of 
blood  is  from  two  different  sources ;  namely,  the  hepatic  artery  and  the 
portal  vein.  The  ramifications  of  the  hepatic  artery  are  distributed 
to  the  walls  of  the  hepatic  ducts  and  of  the  portal  vein,  to  the  capsule 
of  Glisson  and  to  the  peritoneal  covering  of  the  organ ;  while  those 
of  the  portal  vein  pass  into  the  glandular  parenchyma,  and,  after 
traversing  its  substance  as  a  capillary  plexus,  become  continuous  with 
the  rootlets  of  the  hepatic  vein.  Beside  arterial  blood,  accordingly, 
which  the  liver  receives  in  moderate  quantity,  it  is  supplied  with  venous 
blood  in  great  abundance,  conveyed  by  the  portal  system  from  the 
stomach,  the  spleen,  the  pancreas,  and  the  intestine. 

Secondly,  the  liver  is  distinguished  by  its  size.  While  the  weight 
of  all  the  salivary  glands  together,  in  man,  .is  but  little  over  100 
grammes,  and  that  of  the  pancreas  about  75  grammes,  the  liver  forms 
a  compact  vascular  and  glandular  organ,  weighing  nearly  or  quite  1600 
grammes,  and  occupying  a  considerable  portion  of  the  abdominal 
cavity. 

Lastly,  the  liver  differs  so  much  in  texture  from  other  secretory 
organs,  as  to  require  a  special  description.  The  secreting  apparatus 
consists,  as  usual,  of  glandular  cells  and  capillary  blood-vessels,  with 
ducts  for  the  discharge  of  the  secreted  fluid  ;  but  these  elements,  instead 
of  being  arranged  as  elsewhere  in  distinct  groups  of  tubules  or  rounded 
follicles,  are  closely  united,  forming  on  all  sides  a  continuous  mass  by 
mutual  contact  and  adhesion. 

The  substance  of  the  liver  is  divided  into  masses  or  islets,  about  1.5 
millimetre  in  diameter,  known  as  the  hepatic  lobide*.  Those  lobules, 
however,  are  not  anatomically  separate  from  each  other,  but  are  dis- 
tinguishable only  by  the  arrangement  of  the  afferent  and  eil'erent 
blood-vessels.  Each  lobule  is  embraced  by  the  terminal  bnmHics  of 
the  portal  vein,  raiiiilyiim-  bet \veen  the  adjaernt  lobules,  and  known  as 
the  interlobular  veins.  From  the  interlobular  vein  minute  vessels 
pass  into  the  substance  of  the  lobule,  forming  by  their  division  and 


DIGESTION. 


175 


HEPATIC  LOBULE,  in  transverse  section,  showing  the 
distribution  of  its  blood-vessels.— a,  a.  Interlobular  veins. 
6.  Intralobular  vein,  c,  c,  c.  Plexus  of  capillary  blood-vessels 
within  the  lobule,  d,  d.  Twigs  of  interlobular  vein,  passing 
to  adjacent  lobules. 


inosculation  a  capillary  plexus,  the  vessels  of  which  have  a  general  con- 
vergent direction  toward  the  centre  of  the  lobule.  At  this  point  they 
unite  to  form  an  efferent 

vessel,    which,     from     its  FIG.  26. 

position,  is  termed  the 
intralobular  vein,  and 
which  continues  its  course 
until  it  joins  a  small  branch 
of  the  hepatic  vein.  Each 
lobule  is  therefore  a  more 
or  less  ovoid,  cylindrical, 
or  prism  -  shaped  mass, 
resting  upon  a  branch  of 
the  hepatic  vein.  It  is 
attached  to  this  vessel  by 
its  own  intralobular  vein, 
which  passes  through  its 
axis  receiving  the  blood 
collected  from  it ;  while  it 
is  encircled  by  terminal 
branches  of  the  portal  vein, 
which  supply  the  blood 
for  its  interior  circulation. 

Beside      its      capillary 

blood-vessels,  the  lobule  consists  mainly  of  glandular  cells.  These  are 
generally  of  a  five-  or  six-sided  prismatic  form,  often  with  one  or  two 
of  their  borders  excavated  by  curvilinear  furrows  at  the  points  where 
they  are  in  contact  with  a  capijlary  blood-vessel.  They  are,  on  the 
average,  22  mmm.  in  diameter,  finely  granular,  usually,  in  man,  con- 
taining one  or  more  fat  globules,  and  provided  with  a  round  or  oval 
nucleolated  nucleus.  The  cells  are  everywhere  in  contact  with  each 
other  by  their  plane  surfaces,  and  each  one  is  also  in  direct  relation  at 
several  points  with  a  capillary  blood-vessel.  Thus  the  two  elements 
are  intimately  united  throughout  the  substance  of  the  lobule. 

There  is  an  equally  close  connection  between  the  glandular  cells  and 
the  biliary  ducts.  The  main  hepatic  duct,  which  with  its  ramifications 
accompanies  the  divisions  of  the  portal  vein,  breaks  up  into  branches 
which  finally  reach  the  interlobular  spaces.  In  man,  the  biliary  ducts 
of  a  larger  diameter  than  about  200  mmm.  are  lined  with  cylindrical 
epithelium ;  while  in  those  below  100  mmm.  in  diameter,  the  form  of 
the  cells  changes  to  that  of  pavement  epithelium.  The  biliary  ducts 
in  the  interlobular  spaces  are  of  the  smaller  variety,  being  not  more 
than  50  mmm.  in  diameter,  and  lined  with  pavement  epithelium.  They 
break  up  into  communicating  branches,  which  cover  the  lobule  with  a 
plexus  of  biliary  canaliculi. 

From  this  superficial  plexus  the  finest  biliary  tubes  penetrate  the 
lobule  and  there  inosculate  with  each  other  between  the  glandular  cells. 


176  FUNCTIONS    OF    NUTRITION. 

In  the  amphibia  (frogs  and  water-lizards),  as  shown  by  Hering  and 

FIG.  27. 


FINER  BILIARY  CANALS  AND  BILIARY  DUCTS,  from  the  frog's  liver.— a.  Small  biliary  duct,  with 
its  lining  of  epithelium  cells,  b,  c.  Terminal  branches  of  the  minute  biliary  canals,  surrounded 
by  glandular  cells,  d.  Transverse  communicating  branch  between  two  biliary  canals,  e,  e.  Sheath 
of  glandular  secreting  cells,  surrounding  the  biliary  canals  /.  Section  of  capillary  blood-ves- 
sel. (Eberth.) 


FIG.  28. 


Eberth  (Fig.  27),  the  ultimate  structure  of  the  liver  is  not  essentially 

different  from  that  of  other  lobu- 
lated  glands.  The  smaller  biliary 
ducts,  lined  with  pavement  epi- 
thelium, give  off  minute  branches 
which  communicate  with  each 
other  and  are  in  contact  every- 
where with  the  large  glandular 
cells ;  each  terminal  branch  being 
surrounded  by  a  single  sheath 
f  of  such  cells,  representing  the 
\  epithelial  lining  of  a  tube  or 
follicle. 

In  man  and  the  warm-blooded 
quadrupeds,  the  texture  of  the 
liver  is  more  compact,  the  u-land- 
_  $*'£  ular  cells  and  capillary  blood-ves- 

sels more  closely  united,  and  espe- 
cially the  finest  biliary  passages 
within  the  lobule  are  more  abun- 
dant. From  the  plexus  of  cana. 
liculi  on  the  surface  of  the  lobule,  smaller  branches  penetrate  its  inte- 
rior, and  there  inosculate  so  frequently,  that  they  encircle  each  gland- 


r 


TRAN-  TION  OF  PART  OF  A  LOBULE 

i  •1111:  KAIU;II'>   LIVI.K.- -<i.  ,i,  ./.   Niu-lratnl 
glandular  cells.    l>, h,l>.  Capillary  l»ilr-<lm-ts  pa->>- 

,.-l\V(M-n    tin-    adjacrnt    rrlls.      <\  r,  ,-.    Srrtiulls 

of  capillary  I.I.M.il-vrssrN. 


DIGESTION.  177 

ular  cell  with  their  network.  These  interior  communicating  passages 
are  the  capillary  bile-ducts.  They  are  much  smaller  than  the  capillary 
blood-vessels,  being  in  the  rabbit's  liver,  according  to  Kolliker,  not 
more  than  2  mmm.  in  diameter.  They  embrace  the  glandular  cells  in 
such  a  way  that  they  are  always  situated  at  the  greatest  possible  dis- 
tance, that  is,  half  the  diameter  of  a  cell,  from  the  nearest  capillary 
blood-vessel;  the  blood-vessels  running  along  the  edges  of  the  pris- 
matic cells  (Kolliker),  while  the  ducts  pass  along  the  middle  of  their 
plane  surfaces.  Thus  the  two  sets  of  canals,  namely,  capillary  blood- 
vessels and  bile-ducts,  form  a  double  series  of  inosculating  passages 
embracing  the  glandular  cells,  and  directed  at  right  angles  to  each  other. 

Physical  Properties  and  Composition  of  the  Bile. 

The  bile,  as  it  comes  from  the  gall-bladder,  is  a  clear,  more  or  less 
ropy  fluid,  of  neutral  or  alkaline  reaction,  with  a  faint  animal  odor.  Its 
average  specific  gravity,  according  to  various  observers,  is  about  1020. 
If  shaken  with  air,  it  foams  up  into  a  frothy  mixture,  which  remains 
for  a  long  time  on  its  surface.  This  property  depends  on  the  presence 
of  the  biliary  salts,  which  have  the  same  action  in  a  watery  solution. 
The  ropy  character  of  the  secretion  varies  much  at  different  times,  even 
in  the  same  animals,  and  is  due  to  the  mucus  of  the  gall-bladder ;  as 
the  bile  which  flows  directly  from  the  hepatic  ducts  is  always  a  watery 
fluid.  The  longer  it  is  retained  in  the  gall-bladder,  the  more  dense  and 
mucous  is  its  consistency. 

The  color  of  the  bile  varies,  in  different  species  of  animals,  from  a 
f  reddish-orange  to  a  nearly  pure  green,  presenting  all  the  intermediate 
tints  of  golden-yellow,  reddish-brown,  olive-brown,  olive,  yellowish- 
green,  and  bronze-green.  Humanv  bile  from  a  biliary  fistula  was  found 
by  Jacobsen  to  be  clear,  yellowish,  bronze-green ;  that  taken  from  the 
gall-bladder  after  death  is  usually  a  dark  golden-brown.  Dog's  bile  is 
brownish-olive  or  bronze  ;  pig's  bile  reddish-orange  or  reddish-brown  ; 
and  sheep-  and  ox-bile  greenish-olive,  or  more  frequently  nearly  green. 
As  a  rule,  the  bile  of  herbivorous  animals  is  more  decidedly  green,  that 
of  the  carnivora  and  omnivora  orange  or  brown.  These  differences 
may  be  referred  to  two  principal  tints,  corresponding  with  the  two 
coloring  matters  of  bile ;  in  one  of  which  the  predominating  color  is 
red  or  reddish-brown,  dependent  on  bilirubine,  in  the  other  green, 
owing  to  the  presence  of  biliverdtne.  As  their  proportion  varies,  the 
specimen  will  exhibit  a  corresponding  color  of  the  pure  or  mingled  tints. 

The  color  of  the  bile  is  also  modified  by  oxidizing  agents,  which 
produce  a  green  "hue  in  olive  or  brown  bile,  and  increase  the  intensity 
of  the  green  when  this  color  is  already  present.  If  brown-  or  olive- 
colored  bile  be  exposed  for  a  short  time,  its  surface  becomes  green  by 
contact  with  the  atmosphere.  The  change  may  be  instantly  produced 
by  adding  a  few  drops  of  a  watery  solution  of  iodine  ;  and  a  little  nitric 
acid  acts  with  great  energy,  developing  at  once  a  bright  grass-green 
hue.  The  color  of  green  bile,  on  the  other  hand,  disappears  by  exclu- 

M 


178  FUNCTIONS    OF    NUTRITION. 

sion  of  the  atmosphere.  If  ox-bile  of  a  pure  green  or  olive-green  hue 
be  inclosed  in  a  full  and  securely  stoppered  vessel,  so  as  to  be  protected 
from  the  air,  it  gradually  loses  its  green  color,  becoming  a  dull  yellow. 
The  alteration  progresses  from  the  external  parts  of  the  liquid  toward 
its  centre,  until  at  the  end  of  twelve,  twenty-four,  or  thirty-six  hours, 
the  whole  has  become  light  yellow  or  yellowish-brown.  The  green 
hue  may  then  be  restored  by  the  addition  of  iodine,  or  by  exposing 
the  bile  in  thin  layers  to  the  air.  This  change  depends  on  the  conver- 
sion of  bilirubine  by  oxidation  into  biliverdine. 

The  bile  exhibits  a  peculiar  reaction  with  nitroso-nitric  acid,  due  to 
the  effect  on  its  coloring  matter.  If  bile  be  brought  in  contact,  in  a 
cylindrical  glass  vessel,  with  a  layer  of  this  acid,  and  allowed  to  remain 
without  agitation,  a  series  of  colored  rings  are  produced  at  the  surface 
of  contact,  following  each  other  in  definite  order,  from  the  bile  to  the 
nitric  acid,  as  green,  blue,  violet,  red,  and  yellow.  The  colors  repre- 
sent successive  stages  of  the  oxidation  and  final  destruction  of  the  color- 
ing matter.  This  test,  known  as  "  Gmelin's  bile  test,"  may  be  applied 
to  other  animal  fluids  in  which  bilirubine  is  supposed  to  be  present. 

The  bile  presents,  also,  certain  optical  properties  which  distinguish 
it  from  other  animal  fluids. 

First,  it  is  dichroic ;  that  is,  it  has  two  different  colors  by  trans- 
mitted light,  according  to  its  mass.  If  a  specimen  of  ox-bile,  which 
appears  of  a  pure  transparent  green  color  by  ordinary  daylight  in  layers 
of  two  or  three  centimetres,  be  viewed  by  strong  sunlight  in  a  thick- 
ness of  five  or  six  centimetres,  it  is  red.  In  this  respect  it  resembles 
a  solution  of  chlorophylle,  which  presents  the  same  contrast  of  colors 
in  a  very  marked  manner. 

Secondly,  it  is  fluorescent ;  *  that  is,  it  becomes  faintly  luminous 
with  a  color  of  its  own,  when  viewed  by  the  more  refrangible  rays  of 
the  solar  spectrum.  If  a  specimen  of  clear  greenish  bile  be  placed  in 
the  track  of  either  the  violet  or  the  blue  ray  of  the  solar  spectrum,  it 
becomes  visible  with  a  light  yellowish-green  tint.  In  the  green  it  is 
more  yellowish;  and  in  the  yellow  it  has  a  tinge  of  red.  Thus  in  all 
parts  of  the  spectrum  where  it  exhibits  this  property,  it  emits  a  liirht 
of  less  refrangibility  than  that  of  the  ray  by  which  it  is  illuminated. 
Fluorescence  is  also  manifested,  to  a  remarkable  degree,  by  solutions 
of  chlorophylle,  which,  although  of  a  clear  green  color  by  diffused  day- 
light, are  pure  red,  when  viewed  by  either  the  violet,  blue,  green,  or 
yellow  ray  of  the  spectrum. 

The  fluorescence  of  bile  does  not  depend  on  its  coloring  matter,  but 
is  due  mainly  to  the  biliary  salts,  since  it  is  also  exhibited  by  their 

*  This  property,  so  called  from  fliior  spar,  in  which  it  was  first  observed,  is  shown 
by  various  transparent  substances,  when  illuminated  by  solar  light,  or  by  that  of  cer- 
tain parts  of  the  spectrum.  Thus  a  solution  of  quinine  sulphate,  which  is  colorless 
in  ordinary  daylight,  becomes  blue  where  the  sun's  rays  are  concentrated  upon  it  by 
a  lens ;  and  it  exhibits  a  distinct  luminosity  in  both  the  violet  and  ultra-violet  parts 
of  the  spectrum. 


DIGESTION.  179 

watery  or  alcoholic  solutions ;  the  only  difference  being  that  the  color 
of  the  solutions  by  the  violet  and  blue  rays  is  nearly  pure  yellow 
instead  of  yellowish-green. 

The  bile  of  the  inferior  animals  can  be  taken  in  a  state  of  freshness 
and  purity,  and  in  sufficient  quantity  for  examination,  from  the  gall- 
bladder immediately  after  death.  It  has  also  been  collected  by  means 
of  an  artificial  fistula  of  the  gall-bladder  or  of  the  common  biliary  duct. 
Human  bile,  taken  from  the  gall-bladder  some  hours  after  death,  is 
liable  to  be  more  or  less  altered  from  its  normal  condition.  It  has 
been  obtained  in  cases  of  accidental  biliary  fistula  in  man  by  Ranke* 
and  Jacobsen.f  According  to  Jacobsen  its  solid  ingredients  amount 
to  about  22.5  parts  per  thousand ;  a  little  over  one-third  consisting  of 
mineral  salts,  the  remaining  two-thirds  of  organic  matter.  Both  the 
coloring  matters  were  always  present.  The  proportions  of  all  the 
ingredients  were  as  follows : — 

COMPOSITION  OF  HUMAN  BILE,  ACCORDING  TO  THE  ANALYSES  OF  JACOBSEN. 

Water 977.40 

Sodium  glycocholate 9.94 

Cholesterine .         0.54 

Free  fats    ...  0.10 


Organic  , 
matters. 


Mineral 


Sodium  palmitate  and  stearate  .        .        .        .  1.36 

Lecithine     .         ...         .        .         .        .         .  0.04 

Other  organic  matters 2.26 

Sodium  chloride 5.45 

Potassium  chloride  0.28 


salts,     j  Sodium  phosphate 1.33 

I  Lime  phosphate 0.37 

[  Sodium  carbonate 0.93 

1000.00 

In  ox-bile,  as  shown  by  Berzelius,  Frerichs,  and  Lehmann,  the  pro- 
portion of  both  mineral  and  organic  ingredients  may  be  much  greater 
than  the  above,  the  biliary  salts  alone  amounting  to  90  parts  per 
thousand.  Ranke  found  the  average  proportion  of  solid  ingredients 
31.6 ;  and  according  to  Robin  J  and  Hoppe-Seyler,  §  the  biliary  salts  in 
human  bile  from  the  gall-bladder  may  amount  to  from  30  to  100  per 
thousand  parts.  In  Jacobsen 's  case  the  specific  gravity  of  the  bile  was 
but  little  over  1010  ;  and  we  have  found  it,  in  human  bile  from  the  gall- 
bladder, 1018.  The  general  result  of  observations  on  this  point  is  that 
the  bile  becomes  more  concentrated  in  the  gall-bladder,  but  acquires  no 
further  ingredient  except  mucus. 

The  most  important  constituents  of  the  bile,  so  far  as  known,  are 
the  biliary  salts,  sodium  glycocholate  and  sodium  taurocholate,  already 
described  in  Chapter  YI.  These  salts  are  associated  in  the  bile  in 

*  Physiologie  des  Menschen.     Leipzig,  1872,  p.  284. 
f  Kevue  des  Sciences  Me"dicales.     Paris,  1874,  p.  385. 
J  Les  Humeurs.     Paris,  1874,  p.  656. 
\  Physiologische  Chemie.     Berlin,  1878,  pp.  299,  301. 


180 


FUNCTIONS    OF    NUTRITION. 


varying  proportions.  Generally  the  glycocholate  may  be  said  to  pre- 
ponderate in  the  ruminant  animals,  taurocholate  in  the  carnivora.  In 
dog's  and  cat's  bile,  the  taurocholate  exists  alone.  In  human  bile  both 
substances  may  be  present  ;  sometimes  one  being  the  more  abundant, 
sometimes  the  other.  According  to  some  writers  (Robin,  Hardy, 
Gorup-Besanez,  Hoppe-Seyler)  the  taurocholate  exists  alone  or  in 
greater  quantity  ;  according  to  others  (Bischoff,  Lossen,  Ranke)  the 
glycocholate  is  in  larger  proportion.  In  Jacobsen's  case,  sodium  glyco- 
cholate was  invariably  present,  the  taurocholate  being  less  constant. 
We  have  also  found  human  bile  to  contain  the  glycocholate  without 
taurocholate.  As  the  first  of  these  substances  is  produced  from  the 
second,  by  dehydration  and  separation  of  its  sulphur,  it  is  explainable 
why  the  proportions  of  the  two  should  vary  from  time  to  time. 

Mode  of  Secretion  and  Discharge  of  the  Bile.  —  As  in  man  and 
most  animals  the  gall-bladder  forms  a  lateral  receptacle  in  which  the 
bile  is  wholly  or  partially  stored  up  during  a  certain  time,  there  are 
two  points  which  require  separate  investigation  ;  first,  the  manner  and 
rate  of  its  secretion  by  the  liver  ;  and  secondly,  the  time  and  quantity 
of  its  discharge  into  the  intestine. 

In  regard  to  its  mode  of  secretion,  the  experiments  of  Bidder  and 

Schmidt  were  performed  in  the  fol- 
lowing manner  :  They  operated  by 
tying  the  common  bile-duct,  and 
then  opening  the  fundus  of  the  gall- 
bladder, thus  producing  a  biliary 
fistula,  by  which  the  whole  of  the 
bile  was  drawn  off.  By  collecting 
and  weighing  the  fluid  discharged 
at  different  periods,  they  came  to 
the  conclusion  that  the  secretion 
of  bile  never  entirely  ceases  ;  but 
that  it  begins  to  increase  within 
two  and  a  half  hours  after  taking 
food,  to  reach  its  maximum  about 
the  twelfth  or  fifteenth  hour.  Other 
observers  have  obtained  different 
results.  Arnold  found  the  quantity 
largest  soon  after  meals,  decreasing 
again  after  the  fourth  hour.  Kol- 
liker  and  Miiller  found  it  largest 

DUODENAL  FISTULA  IN  THE  DOG.—  a.  Stomach.    ,     .  ,        .    ,,          ,     .    ,    ,    , 

b.  Duodenum,    «,  e,  c.  Pancreas;  its  two  ducts    between  the  Sixth  and  eighth  hours. 
opening    into   the  duodenum,  one  near  the    The  bile  is   therefore    a    Continuous 


FIG.  29. 


variable  in  quantity 
through  the  abdominal  walls  into  the  duo-  at  different  times  ;  being,  according 

to  the  majority  of  observers,  most 
abundant  some  hours  after  the  commencement  of  digestion. 

As  to  its  discharge  into  the  alimentary  canal,  it  is  certain,  in  the  first 


DIGESTION. 


181 


place,  that  bile  is  present  in  the  intestine  at  all  times,  both  during 
digestion  and  in  the  intervals.  This  is  shown  by  examination  of  the 
intestine  in  dogs  killed  at  various  periods  after  feeding.  We  have 
always  found,  under  these  circumstances,  evidence  of  the  biliary  salts 
in  the  ether  precipitate  of  the  alcoholic  extract  of  the  intestinal  contents, 
in  animals  killed  from  one  to  twelve  days  after  the  last  meal.  The 
biliary  substances  were  recognized  both  by  their  solubility  in  water  and 
in  alcohol,  their  insolubility  in  ether,  their  crystalline  form,  and  by  their 
reaction  with  Pettenkofer's  test.  The  secretion  therefore  continues  to 
find  its  way  into  the  alimentary  canal  long  after  the  animal  has  been 
deprived  of  food. 

But  the  quantity  of  bile  passing  into  the  intestine  in  a  given  time  is 
much  influenced  by  the  digestive  process,  and  its  quantity  is  greatest 
soon  after  the  commencement  of  digestion.  We  have  examined  this 
point  by  means  of  a  duodenal  fistula,  made  on  the  same  plan  as  that  for 
gastric  fistulae  (Fig.  29). 

To  ascertain  the  quantity  of  bile  discharged  into  the  intestine,  and 
its  variations  during  digestion,  the  duodenal  fluids  were  drawn  off,  for 
fifteen  minutes  at  a  time,  at  various  periods  after  feeding,  and  examined 
as  follows :  each  separate  quantity  was  evaporated  to  dryness,  its  dry 
residue  extracted  with  alcohol,  the  alcoholic  solution  precipitated  with 
ether,  and  the  ether-precipitate,  representing  the  biliary  salts  present, 
dried,  weighed,  and  treated  with  Pettenkofer's  test.  The  result  is  given 
in  the  following  table.  At  the  eighteenth  hour  the  quantity  of  fluid  was 
so  small  that  the  amount  of  its  biliary  ingredients  was  not  ascertained.  It 
reacted,  however,  with  Pettenkofer's  test,  showing  that  bile  was  present. 

DISCHARGE  OF  INTESTINAL  AND  BILIARY  FLUIDS  FROM  DUODENAL  FISTULA  IN  A 
DOG  WEIGHING  16.5  KILOGRAMMES. 


Time  after 
feeding. 

Quantity  of  fluid 
in  15  minutes. 

Dry  residue  of 
the  same. 

Quantity  of 
biliary  salts. 

Proportion     of 
biliary  salts  in 
the   dry  resi- 
due. 

Immediately. 

(Grammes.) 
41.467 

(Grammes.) 
2.138 

(Grammes.) 
0.648 

(Per  cent.) 
30 

1  hour. 

128.936 

6.803 

0.259 

3 

3  hours. 

50.537 

3.887 

0.259 

7 

6      ' 

48.594 

4.729 

0.227 

5 

9      ' 

55.721 

5.053 

0.291 

6 

12      ' 

21.057 

1.490 

0.243 

16 

15      ' 

22.482 

1.166 

0.259 

22 

18      ' 





— 



21      ' 

24.880 

0.712 

0.064 

9 

24      ' 

10.561 

0.615 

0.210 

34 

25      ' 

9.783 

0.324 

0.194 

60 

The  bile  therefore  passes  into  the  duodenum  in  much  the  largest 
quantity  immediately  after  feeding.  During  the  intervals  of  digestion 
it  accumulates  in  the  gall-bladder ;  and  in  animals  which  have  been 


182  FUNCTIONS    OF    NUTRITION. 

for  some  time  without  food  the  gall-bladder  is  usually  distended  with 
bile,  while  in  those  killed  immediately  or  soon  after  feeding  it  is  com- 
paratively  empty.  At  the  commencement  of  digestion  it  is  excited  to 
contraction,  causing  a  sudden  flow  of  bile  into  the  duodenum.  After 
that  time  the  discharge  remains  nearly  constant ;  not  varying  much,  in 
a  dog  of  sixteen  and  a  half  kilogrammes  weight,  from  250  milligrammes 
of  the  biliary  salts  every  fifteen  minutes,  or  a  little  over  one  gramme 
per  hour. 

Daily  Quantity  of  the  Bile. — The  first  experiments  of  value  on  this 
point  were  those  of  Bidder  and  Schmidt,*  in  1852.  They  were  per- 
formed on  dogs,  cats,  sheep,  and  rabbits,  in  the  following  manner :  A 
ligature  was  first  placed  on  the  common  biliary  duct,  an  opening  then 
made  in  the  fundus  of  the  gall-bladder,  and  the  bile,  discharged  through 
this  opening,  received  in  previously  weighed  vessels,  and  its  quantity 
determined.  The  animal  was  then  killed,  weighed,  and  carefully  exam- 
ined, to  make  sure  that  the  biliary  duct  had  been  securely  tied,  and  that 
no  inflammatory  alteration  had  taken  place.  The  observations,  which 
were  made  at  different  periods  after  feeding,  occupied  in  each  animal 
about  two  hours.  The  average  quantity  for  twenty-four  hours  was 
then  calculated  from  a  comparison  of  the  above  results ;  the  amount  of 
solid  ingredients  being  ascertained  in  each  instance  by  evaporating  a 
portion  of  the  bile  and  weighing  the  dry  residue. 

It  was  found  that  the  daily  quantity  varied  considerably  in  different 
animals,  being  much  greater  in  the  herbivora  than  in  the  carnivora. 
The  results  obtained  were  as  follows : 

DAILY  QUANTITY  PER  KILOGRAMME  OF  BODILY  WEIGHT. 

In  the  cat 
"      dog 


Fresh  bile. 
14.537  grammes. 
19.956         " 
25.372        " 
136.556         " 

Dry  residue. 
0.816  grammes. 
0.985         " 
1.340         " 
2.464        " 

rabbit    . 

According  to  the  later  researches  of  Schiff,f  these  estimates  are  not 
beyond  the  truth,  since  he  obtained  considerably  larger  quantities  in 
the  dog,  by  a  fistula  of  the  gall-bladder,  without  tying  the  common 
biliary  duct.  While  the  average  quantity  obtained  in  this  animal  by 
Bidder  and  Schmidt  was  0.832  gramme  of  fresh  bile  per  hour  for 
every  kilogramme  of  bodily  weight,  in  the  experiments  of  Schiff  it 
was  1.3  to  3.2  grammes  per  kilogramme  per  hour. 

Since  in  man  the  processes  of  digestion  and  nutrition  resemble  those 
of  the  carnivora,  rather  than  those  of  the  herbivora,  it  is  the  former 
which  should  be  selected  as  a  term  of  comparison  for  estimating  the 
daily  quantity  of  bile.  If  we  apply  accordingly  to  the  human  subject 
the  results  obtained  by  Bidder  and  Schmidt  from  the  cat  and  dog,  the 
quantity  of  bile,  for  a  man  weighing  65  kilogrammes,  would  be  a  little 

*  Verdauungflsaefte  und  Stoffwechsel.     Leipzig,  1852. 

f  Archiv  fiir  die  gesanmite  Physiologic.     Bonn,  1870,  Band  iii.,  p.  598. 


DIGESTION.  183 

over  1100  grammes  per  day.  Ranke,*  in  his  case  of  human  biliary 
fistula,  obtained  a  result  not  essentially  different.  The  patient  weighed 
only  47  kilogrammes ;  the  average  quantity  of  bile  discharged  in  twenty- 
four  hours  being  652  grammes,  the  maximum  945  grammes.  In  a  man 
of  65  kilogrammes'  weight  this  would  correspond,  for  the  average,  to 
902  grammes,  and  for  the  maximum  to  1307  grammes.  The  entire 
quantity  of  bile,  therefore,  for  a  man  of  medium  size,  is  evidently  not 
far  from  1000  grammes  per  day.  This  contains  about  30  grammes  of 
solid  ingredients. 

Physiological  Action  of  the  Bile. — Notwithstanding  the  well-marked 
character  of  the  bile,  and  its  frequent  investigation  by  competent  ob- 
servers, its  physiological  action  remains  extremely  obscure.  We  can 
state  only  a  few  points,  which  embrace  nearly  the  whole  of  our  pos- 
itive knowledge  in  regard  to  it. 

In  the  first  place,  the  bile  is  present  in  all  vertebrate  animals  without 
exception,  and  is  discharged  from  the  biliary  duct  into  the  intestine 
near  its  upper  extremity.  This  shows  that  the  secretion  is,  in  some 
way,  of  fundamental  importance,  and  also  that  it  has  a  probable  con- 
nection with  the  digestive  functions. 

But  if  the  bile  be  tested  for  its  digestive  influence  on  the  alimentary 
substances,  it  does  not  exhibit  any  distinct  properties  in  this  respect. 
A  diastatic  action  on  starch,  which  was  attributed  to  it  by  Wittich, 
has  been  found  wanting  by  others,  and  according  to  Ewald  is  of 
inconstant  occurrence,  and  never  well  marked  in  character.  Its  action 
on  fatty  substances  is  but  little  more  characteristic.  It  certainly  has 
the  property  of  dissolving  fats  to  some  extent,  both  in  the  free  form 
and  when  saponified ;  and  such  solvent  power  belongs  also  to  a  watery 
solution  of  the  biliary  salts.  But  kby  far  the  greater  part  of  the  fatty 
substances  in  digestion  are  absorbed  in  the  emulsioned  form,  without 
solution  or  saponification ;  and,  according  to  Hoppe-Seyler,f  the  quan- 
tity of  oily  matter  which  the  bile  can  dissolve  is  far  below  that  absorbed 
from  the  intestine.  A  direct  emulsifying  agency  cannot  be  attributed 
to  the  bile,  since,  when  shaken  up  with  oil,  its  emulsive  effect  is  so  in- 
complete and  temporary  as  to  be  practically  without  importance.  It 
has  been  thought  to  have  an  indirect  action  in  this  respect,  when  the 
fats  are  partially  acidified  and  saponified  by  the  pancreatic  juice,  by 
dissolving  the  saponified  portion,  and  thus  facilitating  the  emulsion  of 
the  remainder.  But  emulsion  takes  place  so  instantly  and  completely 
by  the  contact  of  oil  with  pancreatic  juice,  when  no  bile  is  present,  that 
its  normal  share  in  the  process  can  hardly  be  a  large  one.  As  regards 
the  albuminous  matters,  there  is  no  evidence  that  the  bile  exerts  upon 
them  any  specific  action. 

Another  influence  regarded  as  belonging  to  the  bile  is  that  of  excit- 
ing the  muscular  action  of  the  intestine,  and  thus  serving  as  a  stimulus 

*  Physiologic  des  Menschen.     Leipzig,  1872,  p.  284. 
f  Physiologische  Cheraie.    Berlin,  1878,  p.  315. 


184  FUNCTIONS    OF    NUTRITION. 

to  its  peristaltic  movement.  It  is  no  doubt  true  that  torpidity  of  the  in- 
testine is  a  usual  accompaniment  of  clay-colored  evacuations  from  the 
absence  of  bile ;  and  on  the  other  hand  that  bile,  if  applied  to  the  mus- 
cular coat  of  the  intestine,  will  excite  its  contraction.  But  this  cannot 
be  regarded  as  fully  accounting  for  so  abundant  and  peculiar  a  secretion. 

Furthermore,  the  bile  has  been  thought  to  assist  by  its  physical  prop- 
erties the  absorption  of  oily  matter  by  the  intestine.  It  has  been  shown 
by  direct  experiment  to  aid  the  passage  of  oily  matter  through  organic 
membranes  or  parchment  paper ;  that  is,  oily  matter  will  pass  through 
these  membranes  more  readily  when  they  are  moistened  with  bile  than 
when  simply  wetted  with  water  ;  and  it  is  from  these  experiments  that 
the  supposed  action  of  bile  has  been  inferred.  But  the  villi  of  the  in- 
testine are  not  simply  membranes  moistened  with  water.  They  are 
penetrated  by  alkaline  and  albuminous  fluids,  their  blood-vessels  con- 
tain an  abundance  of  liquid  organic  material,  and  the  fatty  emulsion 
formed  by  the  pancreatic  juice  is  already  adapted  for  absorption. 

Lastly,  the  bile  has  been  credited  with  an  action  antagonistic  to  the 
gastric  juice,  by  which  the  gastric  digestion  is  arrested,  to  be  followed 
by  one  of  a  different  character  in  the  small  intestine.  This  is  based 
on  the  fact  that  the  two  secretions  will  precipitate  with  each  other 
when  mingled  in  a  test-tube.  If  one  or  two  drops  of  dog's  bile  be 
added  to  as  many  cubic  centimetres  of  fresh  gastric  juice  from  the 
same  animal,  a  copious  yellowish-white  precipitate  falls  down,  contain- 
ing the  whole  of  the  coloring  matter  of  the  bile  ;  and  when  filtered,  the 
filtered  fluid  passes  through  colorless.  A  similar  precipitation  takes 
place  if,  instead  of  fresh  bile,  a  watery  solution  of  the  biliary  salts  be 
added  to  gastric  juice.  The  filtered  fluid  retains  its  acid  reaction, 
though  it  has  lost  its  digestive  power. 

But  although  the  biliary  matters  precipitate  by  contact  with  fiv.-h 
gastric  juice,  they  do  not  do  so  with  gastric  juice  holding  peptone  in 
solution.  We  have  invariably  found  that  if  gastric  juice  be  digested 
for  several  hours  at  a  moderate  warmth  with  boiled  white  of  egg,  the 
filtered  fluid,  which  contains  an  abundance  of  peptone,  will  no  longer 
precipitate  with  either  bile  or  a  watery  solution  of  the  biliary  salts, 
even  in  large  amount.  The  gastric  juice  and  bile,  therefore,  do  not 
appear  finally  incompatible  with  each  other  in  digestion,  notwithstand- 
ing their  reaction  when  artificially  mingled. 

The  conclusion  from  these  facts  is  on  the  whole  a  negative  one ;  and 
it  is  the  present  belief  of  most  physiologists  that  we  cannot  with  con- 
fidence assign  to  the  bile  any  direct  influence  in  digestion.  This  accords 
essentially  with  the  result  of  our  own  observations. 

Nevertheless,  there  is  evidence  that  the  bile  is  not  simply  an  ex- 
crementitious  product,  but  that  it  takes  part,  in  the  alimentary  canal, 
in  some  process  essential  to  life.  This  is  shown  by  the  fact  that  if  it 
be  permanently  diverted  from  the  intestine  by  closure  of  the  common 
bile-duct,  and  evacuated  by  a  fistula  of  the  gall-bladder,  the  animals 
gradually  emaciate,  and  die  with  symptoms  of  disordered  nutrition. 


DIGESTION.  185 

This  experiment  has  been  performed  at  least  ten  times  by  Schwann, 
Bidder  and  Schmidt,*  Bernard,  f  and  Flint, J  the  biliary  fistula  remain- 
ing open,  and  the  common  bile-duct,  as  shown  by  subsequent  examina- 
tion, permanently  closed,  so  that  no  bile  found  its  way  into  the  intes- 
tine. The  general  results  in  these  cases  were  alike.  The  animals 
died  in  most  instances  between  the  thirtieth  and  fortieth  day  after  the 
operation.  The  shortest  duration  of  life  was  seven  days,  the  longest 
eighty  days ;  the  average  thirty-six  days.  The  symptoms  were  con- 
stant and  progressive  emaciation,  to  such  a  degree  that  nearly  all 
traces  of  fat  disappeared  from  the  body.  The  loss  of  weight  amounted, 
in  one  case,  to  more  than  two-fifths,  and  in  another  to  nearly  one-half 
that  of  the  whole  body.  There  was  sometimes  falling  off  of  the  hair, 
and  a  putrescent  odor  in  the  feces  and  in  the  breath.  Notwithstanding 
this,  the  appetite  remained  good.  Digestion  was  scarcely  interfered 
with,  and  none  of  the  food  was  discharged  with  the  feces ;  but  there 
was,  in  the  two  cases  of  Bidder  and  Schmidt,  more  or  less  abnormal 
discharge  of  flatus.  There  was  no  pain  ;  and  death  took  place  without 
violent  symptoms,  by  gradual  failure  of  the  vital  powers. 

It  is  also  certain  that  the  bile  disappears  during  its  passage  through 
the  intestine.  We  have  found  that  if  dogs  be  killed  at  various  periods 
after  feeding,  and  the  upper,  middle,  and  lower  portions  of  the  intestinal 
canal  separately  examined,  the  quantity  of  bile  present  diminishes  from 
above  downward.  The  mass  of  intestinal  contents  also  grows  smaller 
and  more  consistent  toward  the  ileo-caecal  valve  ;  their  color  at  the  same 
time  changing  from  light  yellow  to  dark  bronze  or  blackish-green, 
always  strongly  pronounced  in  the  last  quarter  of  the  small  intestine. 
The  ether  precipitate  of  their  alcoholic  extract,  representing  the  biliary 
salts,  is  only  one-fifth  or  one-sixth 'as  abundant,  in  proportion  to  the 
entire  solid  contents,  in  the  large  intestine  as  in  the  small ;  and  if  dis- 
solved in  water,  that  from  both  upper  and  lower  portions  of  the  small 
intestine  always  gives  Pettenkofer's  reaction  in  less  than  a  minute  and 
a  half,  while  in  that  from  the  large  intestine  no  red  or  purple  color  is 
usually  produced,  even  at  the  end  of  three  hours.  Bidder  and  Schmidt§ 
analyzed  all  the  feces  passed  during  five  days  by  a  healthy  dog  weighing 
8  kilogrammes.  From  the  result  of  former  experiments  (page  182)  it 
is  known  that  a  dog  of  this  size  must  have  secreted  during  that  time 
not  far  from  40  grammes  of  solid  biliary  matter ;  while  the  entire 
quantity  of  these  matters  in  the  feces  was  less  than  4  grammes.  The 
acids  of  the  biliary  salts  have  been  found  by  Hoppe-Seyler  in  the  feces, 
both  of  the  dog  and  the  calf;  but  according  to  his  own  estimate ||  their 
quantity,  as  discharged  with  the  excrement,  is  always  insignificant  in 
proportion  to  that  secreted  in  a  corresponding  time. 

*  Verdauungssaefte  und  Stoffwechsel.     Leipzig,  1852,  p.  103. 
f  Liquides  de  TOrganisme.     Paris,  1859,  tome  ii.,  p.  199. 
t  Physiology  of  Man.     New  York,  1867,  p.  369. 
\  Verdauungssaefte  und  Stoffwechsel.     Leipzig,  1852,  p.  217. 
|j  Physiologische  Chemie.     Berlin,  1878,  p.  337. 


186  FUNCTIONS    OF    NUTRITION. 

The  biliary  matters,  therefore,  are  either  so  decomposed  in  the 
intestine  as  to  lose  their  distinctive  reactions,  or  they  are  reab- 
sorbed  in  some  form  by  the  mucous  membrane,  and  again  intro- 
duced into  the  circulation.  It  seems  highly  probable  that  they  are 
reabsorbed.  In  the  experiments  of  Bidder  and  Schmidt,  above  quoted, 
this  point  was  examined  by  elementary  analysis  of  the  fecal  ingredi- 
ents. In  dog's  bile  the  only  or  preponderating  biliary  salt  is  the 
taurocholate,  which  contains  sulphur.  If  the  taurocholate  had  been 
simply  decomposed  or  transformed  in  the  intestine,  so  as  to  be  undis- 
tinguishable  by  Pettenkofer's  test,  its  sulphur  ingredient  would  still  be 
found  in  the  feces.  But  in  the  animal  subjected  to  experiment,  the 
sulphur  ingredient  of  the  bile  secreted  during  five  days  would  amount 
to  2.364  grammes ;  while  only  0.385  gramme  of  sulphur  was  contained 
in  the  feces  for  the  same  time,  and  of  this  only  0.155  gramme  could 
have  been  derived  from  biliary  substances.  That  is,  not  more  than 
one-fifteenth  part  of  the  sulphur  originally  present  in  the  bile  could 
be  detected  in  the  feces. 

A  further  evidence  of  the  reabsorption  of  biliary  matters  from  the 
intestine  is  furnished  by  the  experiments  of  Schiff,*  which  were  con- 
ducted on  a  different  plan.  This  observer  found  that,  under  ordinary 
conditions,  less  pressure  is  required  to  make  a  fluid  pass  from  the 
hepatic  duct  into  the  gall-bladder  than  to  force  it  into  the  intestine. 
Unless,  therefore,  the  pressure  in  the  gall-bladder  be  increased,  either 
by  distention  or  by  muscular  contraction,  it  passes  into  the  gall-bladder 
more  readily  than  into  the  intestine ;  and  a  cystic  fistula,  if  kept  freely 
open,  will  be  sufficient  to  discharge  externally  nearly  all  the  secreted 
bile.  Schiff  demonstrated  this  by  establishing  in  the  same  animal  a 
fistula  of  the  gall-bladder  and  one  of  the  duodenum.  So  long  as  the 
cystic  fistula  remained  open  no  biliary  matters,  or  only  insignificant 
traces  of  them,  could  be  found  in  the  duodenum. 

On  the  other  hand,  when  the  cystic  fistula  was  closed,  the  bile  passed 
through  the  common  duct  into  the  intestine,  thus  maintaining  the 
animal  in  a  healthy  condition.  At  any  time,  by  opening  the  fistula  and 
emptying  the  gall-bladder,  the  rate  of  secretion  might  be  ascertained. 

Schiff 's  observations  show  that  by  leaving  open  the  fistula,  and  thus 
diverting  the  bile  from  the  intestine,  its  rate  of  secretion  is  at  once 
diminished  ;  so  that  at  the  end  of  twenty-four  hours,  if  the  influence  of 
digestion  be  eliminated,  it  is  reduced  to  a  minimum,  which  afterward 
continues  with  only  insignificant  fluctuations.  But  if  the  fistula  be 
closed  for  some  hours,  the  quantity  of  bile  again  rises  to  its  normal 
standard. 

The  same  observer  obtained  similar  results  by  making,  in  the  doir,  a 
duodenal  fistula,  through  which  a  canula  was  introduced  into  the  com- 
mon bile-duct.  The  canula  had  a  lateral  oprninir  near  its  end,  which 
might  be  left  open  or  closed  by  shifting  the  position  of  an  inner  tube 


*  Archiv  fur  die  gesummtu  Physiologic.     Bonn,  1870,  p.  598. 


DIGESTION. 

fitting  closely  in  its  cavity.  Thus  the  bile  might  be  either  discharged 
externally  from  the  orifice  of  the  canula,  or  allowed  to  pass  into  the 
duodenum  by  its  lateral  opening.  It  was  found  that,  after  being  dis- 
charged externally  for  two  or  three  hours,  its  rate  of  secretion  was 
much  less  than  if  it  had  been  allowed  to  pass  into  the  intestine.  The 
results,  in  a  dog  weighing  12  kilogrammes,  were  as  follows: 

CUBIC  CENTIMETRES  OF  BILE  OBTAINED  IN  TEN  MINUTES  AFTER  HAVING  BEEN 

FOE  Two  OE  THREE  HOURS, 

Evacuated  externally.  Discharged  into  the  duodenum. 

2.2  6.0 

2.3  5.4 
2.1  5.6 
2.0  6.2 

1.8  6.5 

1.9  5.7 
Average       .     2.05                                                       5.90 

Thus  the  quantity  of  bile  secreted,  when  allowed  to  follow  its  natu- 
ral course,  is  nearly  three  times  as  great  as  when  it  is  evacuated  exter- 
nally. It  cannot  be  assumed  from  this  that  the  biliary  ingredients  are 
returned  directly  to  the  liver,  and  again  discharged  with  the  bile ;  but 
it  is  difficult  to  avoid  the  conclusion  that  its  ingredients  are  absorbed 
from  the  intestine,  and  supply  in  some  way  the  materials  for  continued 
secretion. 

Finally,  Tappeiner*  has  detected  the  biliary  salts,  by  Pettenkofer's 
test,  in  chyle  from  the  thoracic  duct.  With  150  cubic  centimetres  of 
chyle,  taken  from  the  duct  two  hours  after  feeding,  in  a  dog  weighing 
8  kilogrammes,  he  obtained  a  complete  biliary  reaction  by  the  above 
test. 

As  a  rule,  however,  the  biliary  salts  appear  to  undergo,  before  absorp- 
tion, some  change  which  modifies  their  original  properties ;  and  attempts 
to  distinguish  them  in  the  blood  of  the  portal  vein  have  constantly  met 
with  a  negative  result.  The  most  appropriate  method  for  such  an 
investigation  is  to  collect  the  portal  blood  immediately  after  killing  the 
animal  by  section  of  the  medulla,  coagulate  it  by  the  gradual  addition 
of  alcohol,  or  by  boiling  with  water  and  sodium  sulphate  in  excess, 
evaporate  it  to  dryness,  extract  the  dry  residue  with  absolute  alcohol, 
and  precipitate  the  filtered  alcoholic  solution  by  ether  in  excess.  The 
ether  precipitate  is  then  dissolved  in  water,  and  subjected  to  Petten- 
kofer's test. 

We  have  examined  the  portal  blood,  by  this  method,  in  the  dog,  one, 
four,  six,  nine,  eleven  and  a  half,  twelve,  and  twenty-four  hours  after 
feeding.  The  result  shows  that  in  the  venous  blood,  both  of  the  portal 
vein  and  of  the  general  circulation,  there  is  a  substance  soluble  in  water 
and  in  alcohol,  and  precipitable  by  ether  from  its  alcoholic  solution. 

*  Sitzungsberichte  der  Akademie  der  Wissenschaften.  Wien,  1878.  Band  Ixxvii. 
Abth.  iii.,  p.  286. 


188  FUNCTIONS    OF    NUTRITION. 

This  substance  is  often  considerably  more  abundant  in  the  portal  blood 
than  in  that  taken  from  the  general  venous  system.  It  resembles  the 
biliary  matters  in  consistency,  and  dissolves,  like  them,  with  great 
readiness  in  water ;  but  in  no  instance  have  we  obtained  from  it  a 
characteristic  reaction  with  Pettenkofer's  test.  This  is  not  because  the 
reaction  is  masked  by  other  ingredients  of  the  blood ;  for  if,  at  the 
same  time,  bile  be  added  to  blood  taken  from  the  abdominal  vena  cava, 
in  the  proportion  of  one  drop  of  bile  to  seven  or  eight  cubic  centimetres 
of  blood,  and  the  two  specimens  treated  alike,  the  ether-precipitate  may 
be  considerably  more  abundant  in  the  case  of  the  portal  blood ;  and  yet 
that  from  the  blood  of  the  vena  cava,  dissolved  in  water,  will  give  Pet- 
tenkofer's reaction  perfectly,  while  that  of  the  portal  blood  will  yield 
no  such  reaction. 

The  bile,  accordingly,  is  a  secretion  which  has  not  yet  accomplished 
its  function  when  secreted  and  poured  into  the  intestine.  Although  its 
most  abundant  discharge  coincides  with  the  beginning  of  digestion,  it 
docs  not  seem  to  aid  the  operation  of  the  digestive  fluids,  but  rather  to 
be  itself  acted  on  by  them,  and  converted  into  other  forms  of  combina- 
tion. The  intestine  is,  therefore,  for  the  biliary  ingredients,  a  place  of 
passage,  where  they  undergo  an  intermediate  transformation  between 
their  production  in  the  liver  and  their  final  disappearance  in  other  parts. 
It  is  still  unknown  what  new  substances  are  produced  by  these  changes ; 
but  they  seem  to  be  essential  for  general  nutrition,  which  cannot  be  long 
maintained  if  the  biliary  matters  are  permanently  withdrawn  from  the 
system. 

Intestinal  Juice. 

The  secretory  apparatus  of  the  small  intestine  consists  of  two  sets 
of  glandular  organs;  first,  Brunner's  glands,  which  are  tabulated 
glandules,  confined  to  the  upper  part  of  the  duodenum,  for  a  distance 
of  several  centimetres  from  the  pylorus ;  and,  secondly,  the  follicles  of 
Lieberkuhn,  which  are  simple  tubular  glandules,  occupying  the  sub- 
stance of  the  mucous  membrane  for  the  whole  length  of  the  small  in- 
testine. 

FIG.  30. 

....a 


LONGITUDINAL  SECTION  OP  WALL  OF  DUODENUM  IN  THK  Doo;  showing  the  submucous  layer  of 
Brunner's  Glands.—  a.  Mucous  membrane.  6.  Layer  of  gubmucous  connect  ivr  tissue,  in  which  the 
glands  are  situated,  c.  Muscular  coat.  d.  Peritoneal  rout.  e.  Brunuer's  glaiids,  with  their  ducts 
opening  on  the  free  surface  <>f  the  mucous  meml.nme. 


Brunner's  glands,  or  the  duodenal  glandules,  are  situated  in  the  sub- 
mucous  layer  of  connective  1  issue  in  the  duodenum.  They  are  spheri- 
cal, or,  when  thickly  set,  irregularly  polygonal  in  shape  from  mutual 
pressure,  and  from  ^  to  1  millimetre  in  diameter. 

In  structure,  they  resemble  the  tabulated  glandules  of  the  mouth, 


DIGESTION. 


189 


being  composed  of  rounded  follicles  clustered  about  a  central  excretory 
duct.  Each  follicle  is  about  T'0  of  a  millimetre  in  diameter,  and  consists 
of  a  membranous  wall,  lined  with  nucleated  cells  of  glandular  epithe- 
lium. The  follicles  collected  round  each  terminal  branch  of  the  duct 
are  bound  together  by  a  thin  layer  of 
connective  tissue,  and  covered  with  a  FIG.  31. 

plexus  of  capillary  blood-vessels. 

The  follicles  of  Lieberkiihn,  which  are 
much  more  numerous  than  the  preced- 
ing, occupy  the  entire  thickness  of  the 
mucous  membrane.  They  are  nearly 
straight  tubules,  from  y1^  to  ^  of  a  milli- 
metre in  diameter,  lined  with  cylindrical 
epithelium,  opening  on  the  free  surface 
of  the  mucous  membrane,  and  terminat- 
ing below  by  rounded  extremities.  They 
are  so  thickly  set  that,  for  the  most  part, 
there  appears  to  be  no  space  between  Portion  of  one  of  BR~NNER,S  GLANDS. 
them,  except  that  occupied  by  capillary  from  human  intestine, 

blood-vessels. 

The  fluid  produced  by  the  mucous  membrane  of  the  small  intes- 
tine consists  of  the  secretions  of  these  two  sets  of  glands.  But  owing 
to  the  situation  of  Brunner's  glands,  their  secretion  is  always  mixed 

with  other  fluids ;  and  by  the 
intestinal  juice  proper  is  under- 
stood the  secretion  of  Lieber- 
kiihn's  follicles.  It  is  by  no 
means  easy  to  obtain  this  fluid 
in  pure  form  and  normal  con- 
dition. The  follicles  have  no 
single  excretory  duct,  in  which 
a  canula  might  be  inserted ;  and 
a  fistulous  opening  in  the  intes- 
tine would  yield  a  mixture  of 
all  the  secretions  discharged 
into  its  cavity.  If  these  should 
be  shut  off  by  a  ligature  applied 
above  the  fistula,  the  disturb- 
ance of  the  digestive  process 
would  be  so  great,  that  the  ex- 
periment could  hardly  be  ex- 
pected to  give  valuable  results. 
Nevertheless,  attempts  have  been  made,  by  various  methods,  to 
obtain  the  intestinal  juice  for  examination.  Bidder  and  Schmidt  tied 
the  biliary  and  pancreatic  ducts,  and  then  established  an  intestinal  fis- 
tula below,  from  which  they  extracted  the  fluids  accumulated  in  the 
gut.  Frerichs  operated  by  opening  the  abdomen,  taking  out  a  loop  of 


FIG.  32. 


FOLLICLES  OF  LIEBEKKUHN; 
of  dog. 


from  small  intestine 


190  FUNCTIONS    OF    NUTRITION. 

intestine,  emptying  it  so  far  as  possible  by  gentle  pressure,  isolating 
its  cavity  by  the  application  of  two  ligatures  15  or  20  centimetres  apart, 
and  returning  it  to  the  abdominal  cavity.  After  a  few  hours  the 
animal  was  killed,  and  the  fluid,  which  had  collected  in  the  isolated 
portion  of  the  intestine,  taken  out  and  examined.  Colin  adopted  a 
similar  method,  in  the  horse,  with  greater  precautions.  While  diges- 
tion was  in  full  activity  he  took  out,  through  an  opening  in  the  flank, 
a  loop  of  small  intestine,  which  he  isolated  by  two  compressors,  made 
of  flat  wooden  or  metallic  strips,  enveloped  by  velvet  ribbon,  and  fast- 
ened in  such  a  way  that  the  inner  surfaces  of  the  intestine  were  retained 
in  close  contact,  without  bruising  their  tissues.  The  compressors  being 
applied  from  one  to  two  metres  apart  after  the  included  portion  of  in- 
testine had  been  emptied  by  gentle  pressure,  the  whole  was  returned 
into  the  abdomen,  the  wound  closed  by  sutures,  and  the  animal  killed  at 
the  end  of  half  an  hour. 

On  the  average,  100  grammes  of  fluid  had  accumulated  within  this 
time.  It  was  clear,  with  a  slightly  yellowish  or  amber  tint,  alkaline  in 
reaction,  and  with  a  specific  gravity  of  1010.  According  to  the  analysis 
of  Lassaigne,  it  was  composed  as  follows : 

COMPOSITION  OF  INTESTINAL  JUICE  FROM  THE  HORSE. 

Water •  981.0 

Albuminous  matter 4.5 

Sodium  chloride 
Potassium  chloride 
Sodium  phosphate 
Sodium  carbonate 


1000.0 

Thiry  separated  a  portion  of  the  small  intestine  from  the  remainder 
by  two  transverse  sections,  leaving  the  mesentery  and  vessels  of  the 
isolated  portion  uninjured,  and  then  united  by  sutures  the  divided  ends 
of  the  remaining  portions,  so  as  to  reestablish  the  continuity  of  the 
intestine,  but  with  a  portion,  10  or  15  centimetres  long,  left  out.  Of 
this  isolated  portion,  still  nourished  by  its  blood-vessels,  he  closed  one 
end  by  sutures,  so  as  to  make  of  it  a  blind  extremity,  while  the  other 
he  fastened  to  the  edges  of  the  external  wound  in  such  a  way  as  to 
make  a  permanent  fistula.  When  the  parts  had  healed,  and  natural 
digestion  was  reestablished,  he  collected  the  fluid  discharged  from  the 
isolated  portion  of  intestine.  This  operation  has  been  repeated  by  other 
observers.  The  objection  to  it  is  that  the  isolated  portion  of  intestine, 
after  being  for  some  weeks  precluded  from  taking  part  in  the  process 
of  digestion,  becomes  partially  atrophied,  and  cannot  be  relied  on  as 
furnishing  a  secretion  similar  to  the  normal  intestinal  juice.  The  results 
obtained  vary,  some  of  them  indicating  that  the  secretion  converts  starch 
Into  sugar,  and  has  a  dissolving  action  on  coagulated  albuminous  m Jit- 
ters, others  that  these  properties  are  absent  or  but  slightly  developed. 
Colin  found  that  the  fluid  obtained  from  the  horse  by  his  method  had 


DIGESTION. 

the  power  of  slowly  transforming  starch-paste  into  glucose,  and  that  it 
could  emulsify  oily  substances  with  considerable  energy.  Bernard  found 
the  same  properties  in  a  fluid  obtained  from  the  dog,  by  opening  the 
small  intestine  after  some  days'  fasting.  But  on  the  whole  these  results 
have  not  been  very  satisfactory,  owing  to  the  doubt  how  far  the  fluids 
obtained  represent  the  normal  secretion  of  the  intestine. 

Furthermore,  two  instances  of  intestinal  fistula  have  been  observed 
in  man.  In  the  case  examined  by  Busch,*  the  patient,  a  woman,  31 
years  of  age,  had  been  gored  by  a  steer ;  causing  a  fistulous  opening  in 
the  abdominal  wall,  midway  between  the  umbilicus  and  the  pubis.  It 
communicated  with  the  small  intestine  very  near  its  upper  extremity, 
the  two  portions  of  intestine  being  completely  separated  from  each  other 
at  the  fistula.  The  portion  of  intestine  below  the  fistula,  accordingly, 
contained  none  of  the  fluids  from  above,  but  only  its  own  secretion. 
Busch  operated  by  introducing  into  the  lower  portion  of  the  intestine 
various  alimentary  substances,  and  ascertaining  how  far  they  were 
liquefied  and  absorbed.  He  concluded  that  there  was  a  perceptible, 
but  not  very  energetic,  solvent  action  on  albuminous  matters,  a  much 
stronger  one  on  starchy  substances,  and  either  very  little  or  none  at  all 
on  fat. 

The  case  of  Demantf  was  somewhat  similar,  except  that  the  fistu- 
lous separation  between  the  two  portions  of  small  intestine  was  near 
its  lower  instead  of  its  upper  extremity.  It  was  the  result  of  an  opera- 
tion for  strangulated  hernia  in  a  man  forty-two  years  of  age,  and  at 
the  time  of  the  observation  in  good  health  and  condition.  Demant  col- 
lected the  fluids  secreted  by  the  lower  portion  of  the  intestine,  and  ex- 
perimented with  them  on  different  kinds  of  food  by  artificial  digestion 
at  the  temperature  of  36°  to  38°  1C.  He  found  the  intestinal  juice 
very  scanty,  exuding  from  the  fistula  usually  in  drops.  The  largest 
quantity  obtained  was  25  cubic  centimetres  per  day ;  the  average  from 
15  to  20  cubic  centimetres.  It  was  a  thin,  clear,  alkaline  fluid,  not 
coagulable  by  heat,  but  precipitable  by  acetic  acid  owing  to  its  mucous 
ingredients.  It  contained  no  pepsine  ferment,  had  no  transforming 
action  on  albuminous  matters,  and  produced  no  peptone  from  coagu- 
lated fibrine,  even  after  a  digestion  of  twelve  hours.  It  slowly  trans- 
formed starch  paste  into  glucose,  requiring  five  hours'  time  for  that 
purpose.  Oily  matters,  containing  free  fatty  acid,  were  emulsioned  by 
it,  but  it  had  no  perceptible  effect  on  neutral  fats. 

From  these  observations  it  appears  that  the  intestinal  juice  cannot 
be  an  abundant  secretion,  nor  a  very  active  agent  in  the  digestive 
process.  It  is  an  alkaline  fluid,  with  a  moderate  transforming  action 
on  starchy  matters,  much  inferior  to  that  of  the  pancreatic  juice.  Its 

*  Archiv  fur  pathologische  Anatomie  und  Physiologic.  Berlin,  1858,  Band  xiv., 
p.  140. 

f  Archiv  fur  pathologische  Anatomie  und  Physiologic.  Berlin,  1879,  Band  Ixxv., 
p.  419. 


192 


FUNCTIONS    OF    NUTRITION. 


FIG.  33. 


emulsifying  action  on  fats  is  also  quite  secondary  in  importance,  and  its 
power  of  digesting  albumenoid  substances  doubtful  or  imperfect.  Its 
most  important  property  is  perhaps  the  simple  one  of  lubricating  the 

mucous  membrane,  and  facilita- 
ting the  passage  of  alimentary 
materials  through  the  intestine. 
Digestion  in  the  Intestine. — 
The  digestive  process,  which 
commences  in  the  stomach  under 
the  influence  of  the  gastric  juice, 
is  continued  and  completed  dur- 
ing the  passage  of  the  food 
through  the  small  intestine.  Its 
details  may  be  examined  in  suc- 
cessive parts  of  the  alimentary 
canal,  in  animals  killed  while 
digestion  is  going  on.  After 
a  meal,  consisting  of  muscu- 
lar flesh  and  adipose  tissue, 
the  stomach  contains  (Fig. 
33)  masses  of  softened  meat, 
smeared  with  gastric  juice,  and 
a  moderate  quantity  of  grayish 
This  fluid  contains  isolated  mus- 


CONTENTS  OF  STOMACH  DURING  DIGESTION  OF  MEAT, 
from  the  Dog.— a.  Fat  Vesicle,  filled  with  opaque, 
solid,  granular  fat.  6,  b.  Partially  disintegrated 
muscular  fibre,  c.  Oil  globules. 

grumous  fluid  with  an  acid  reaction. 

cular  fibres,  more  or  less  reduced  to  fragments.     The  fat  vesicles  of 


Fio.  34. 


FIG.  35. 


FROM  DUODENUM  OF  DOG  DURING  DIGESTION 
HI  MKAT.— a.  Fat  vesicle,  with  ita  contents 
diminishing.  The  vesicle  is  beginning  to 
shrivel  and  the  fat  breaking  up.  6,  b.  Disinte- 
grated muscular  fibre,  c,  c.  Oil  globules. 


FROM  MIDDLE  OF  SMALL  INTESTINE.— a,  a.  Fat 

vesicles,  nearly  emptied  of  their  contents. 


beef  are  but  little  altered,  and  there  are  only  a  few  free  oil  globules  in 
the  mixed  fluids  of  the  stomach.     In  the  duodenum  the  muscular  fibres 


DIGESTION. 


193 


FIG.  36. 


are  further  disintegrated  (Fig.  34).  They  are  much  broken  up,  pale 
and  transparent,  but  can  still  be  recognized  by  their  characteristic  mark' 
ings  and  striations.  The  fat  vesicles  also  become  altered  in  the  duo- 
denum. The  solid  granular  fat  of  beef  becomes  liquefied  and  emul- 
sioned ;  and  appears  under  the 
form  of  free  oil  drops  and  fatty 
molecules;  while  the  fat  vesicle 
is  partially  emptied,  and  more  or 
less  collapsed.  In  the  middle  and 
lower  parts  of  the  small  intestine 
(Figs.  35  and  36)  these  changes 
continue.  The  muscular  fibres 
become  more  disintegrated,  pro- 
ducing a  large  quantity  of  granu- 
lar debris,  which  is  at  last  dis- 
solved. The  fat  also  progres- 
sively disappears,  and  the  vesicles 
may  be  seen  in  the  lower  part  of 
the  intestine  completely  collapsed 
and  empty. 

T«  +k;o, ,          4-1*^  A-        4.-          f  ±T~      FROM  LAST  QUARTER  OF  SMALL  INTESTINE.— -a, 

In  this  way  the  digestion  of  the     0.  Fat  vesicleS)  quite  empty  and  shrivelled. 
food  goes  on  continuously  through- 
out the  small  intestine.    At  the  same  time  it  results  in  the  production  of 
three  different  substances,  namely :  1st.  Peptone,  from  the  digestion  of 
albuminous  matters  ;  2d.  Chyle,  from  the  emulsion  of  the  fats ;  and  3d. 
Glucose,  produced  by  the  transformation  of  starch.     These  substances 
are  then  ready  to  be  taken  into  the  circulation ;  and  as  the  mingled  in- 
testinal contents  pass  successively  downward,  the  products  of  digestion, 
together  with  the  digestive  secretions,  are  absorbed  by  the  mucous  mem- 
brane and  carried  away  by  the  blood-vessels. 

The  Large  Intestine  and  its  Contents. 

The  mucous  membrane  of  the  large  intestine  is  provided  with  tubular 
follicles  not  essentially  different  in  their  anatomical  characters  from  the 
follicles  of  Lieberkuhn.  Their  secretion,  however,  appears  to  be  scanty. 
According  to  Hanke,  fistulous  openings  in  the  large  intestine  do  not  yield 
any  notable  quantity  of  fluid,  and  if  a  loop  of  the  gut  be  isolated  by  liga- 
tures, an  accumulation  of  mucus-like  matter  is  the  only  result.  In  the 
rabbit,  after  ligature  of  the  vermiform  appendix,  Funke  obtained,  at  the 
end  of  from  two  to  four  hours,  a  quantity  of  turbid  alkaline  secretion 
with  which  the  appendix  had  become  filled.  This  fluid  was  without 
action  on  coagulated  albumen  ;  but  it  transformed  starch  into  sugar,  and 
also  decomposed  the  sugar  with  production  of  lactic  and  butyric  acids. 
The  same  change  was  produced  on  starch  introduced  into  the  cavity 
of  the  appendix.*  This  accounts  for  the  acid  reaction  sometimes  found 


*  Kauke,  Physiologic  des  Menscheii. 

N 


Leipzig,  1872,  p.  297. 


194  FUNCTIONS     OF    NUTRITION. 

in  the  caecum  of  herbivorous  animals,  although  the  mucous  surface  of 
the  large  intestine  is  constantly  alkaline. 

As  the  remnants  of  the  alimentary  mass  pass  the  ileo-caecal  valve 
into  tlir  large  intestine,  they  acquire  a  pasty  consistency  and  a  repulsive 
odor.  Both  these  changes  become  more  marked  in  the  middle  and  lower 
part  of  the  gut,  until  all  the  superfluous  fluids  have  disappeared,  and  the 
consistency  and  odor  of  the  feces  are  fully  developed.  This  is  not  a 
putrefactive  odor,  but  is  characteristic  of  the  contents  of  the  large  in- 
testine. Its  source  may  be  either  a  peculiar  transformation  of  some 
of  the  ingredients  of  the  food,  or  an  excretory  action  of  the  intestinal 
mucous  membrane.  It  is  probably  in  great  part  the  result  of  an  excre- 
tion, since  in  different  animals,  whatever  the  nature  of  their  food,  the 
feces  have  usually  a  distinct  odor  characteristic  of  the  species. 

The  average  daily  quantity  of  feces  in  man  is  150  grammes,  of  which 
about  75  per  cent,  is  water  and  25  per  cent,  solid  residue.  They  consist, 
first,  of  undigested  remnants  of  the  food,  and  secondly,  of  excreted  mate- 
rial from  the  alimentary  canal.  The  undigested  substances  derived  from 
the  food  are  mainly  animal  or  vegetable  tissues,  which,  from  their  con- 
stitution, are  incapable  of  digestion.  These  are  elastic  fibres,  or  bits  of 
elastic  tissue,  which  nearly  always  pass  the  intestine  unchanged ;  shreds 
of  tendon  or  fascia  not  sufficiently  softened  by  cooking ;  horny  epidermic 
tissues,  both  animal  and  vegetable ;  and  the  spiral  tubes  and  ducts  of 
vegetable  substances.  The  excreted  materials  are  the  mucus  of  the  large 
intestine  and  probably  also  the  volatile  substances  which  produce  the 
fecal  odor.  The  coloring  matters  of  the  bile  are  present  in  a  more  or 
less  altered  form. 

The  mineral  salts  in  the  feces  amount  to  a  little  over  one-tenth  of 
the  solid  ingredients.  They  are  for  the  most  part  the  same  with  those 
of  the  animal  fluids  in  general,  but  are  mingled  in  different  proportions ; 
only  about  4  per  cent,  consisting  of  the  soluble  chlorides  and  sulphates, 
while  fully  80  per  cent,  are  composed  of  lime  and  magnesium  phos- 
phates. They  are  regarded  as  derived  partly  from  the  unabsorbed 
mineral  ingredients  of  the  food,  and  partly  from  the  intestinal  secretions. 


FIG.  37. 


CHAPTER  II. 
ABSORPTION. 

THE  absorption  of  the  digested  food,  which  is  the  main  office  per- 
formed by  the  small  intestine,  is  provided  for  by  a  special  struct- 
ure of  its  mucous  membrane.  The  apparatus  consists  in  an  abundance 
of  minute  eminences  or  prolongations,  the  so-called  villi  of  the  small 
intestine,  so  closely  set  over  its  surface  as  to  give  it  a  characteristic  velvety 
appearance.  They  are  found  throughout  this  part  of  the  alimentary 
canal,  from  the  pylorus  to  the  free  border  of  the  ileo-caecal  valve,  most 
abundant  in  the  duodenum  and  jejunum,  rather  less  so  in  the  ileum,  but 
averaging  in  number  from  20  to  40  to  the  square  millimetre.  In  the 
upper  part  of  the  intestine  they  are  flattened  and  leaf-life,  cylindrical  or 
filamentous  in  its  middle  and  lower  portions  In  man 
they  are  about  one-half  a  millimetre  in  length. 

Each  villus  is  covered  with  nucleated,  finely  gran- 
ular cylindrical  epithelium  cells,  closely  united  with 
each  other  by  their  lateral  surfaces,  and  presenting 
at  their  outermost  portion  a  transparent  layer, 
marked,  according  to  Kolliker,  Frey,  and  other 
observers,  by  fine  vertical  striations.  It  is  pene- 
trated below  by  blood-vessels  from  a  terminal  twig 
of  the  mesenteric  artery,  which  form  by  their  divi- 
sion and  inosculation  a  capillary  net-work  beneath 
the  epithelial  layer.  At  its  base  they  reunite  to 
form  a  venous  branch,  one  of  the  rootlets  of  the 
mesenteric  vein. 

In  the  deeper  part  of  the  villus,  and  nearly  in  its 
longitudinal  axis,  there  is  the  commencement  of  a 
lymphatic  vessel,  which,  after  its  emergence,  joins 
the  general  abdominal  system  of  lymphatic  or 
lacteal  vessels.  It  is  usually  single  in  the  filiform 
and  cylindrical  villi,  double  or  triple  in  those  of 
more  flattened  form.  It  has  exceedingly  thin  walls, 
consisting  of  a  single  layer  of  flattened  epithelium 
cells. 

Closed  Follicles  of  the  Small  Intestine. — In 
addition  to  the  follicles  of  Lieberkuhn,  the  intestine 
presents  two  sets  of  glandular-looking  organs, 
known  as  the  glandulse  solitarise  and  the  glandulae 
agminatse.  The  first  of  these,  or  the  solitary  glandules,  are  found  in 
the  upper  part  of  the  intestine,  scattered  over  its  surface,  as  minute 

195 


AN  INTESTINAL  VILLUS. 
a.  Layer  of  cylindrical 
epithelium,  with  its  ex- 
ternal transparent  stri- 
ated portion.  6,  6. 
Blood-vessels  entering 
and  leaving  the  villus. 
c.  Lymphatic  vessel  oc- 
cupying its  central 
axis.  (Leydig.) 


196  FUNCTIONS    OF    NUTRITION. 

whitish  points.  Farther  down  they  occur  in  clusters  of  several 
together,  and  in  the  lower  part  of  the  jejunum  and  in  the  ileum  they 
constitute  rounded  or  oval  patches,  from  1A  to  5  centimetres  in  length, 
known  as  "  Peyer's  patches."  These  patches  are  situated  opposite  the 
attachment  of  the  mesentery,  with  their  long  diameter  parallel  to  the 
axis  of  the  intestine. 

The  structure  of  the  solitary  glandules  and  of  those  forming  Peyer's 
patches  is  the  same. 

Each  follicle  is  a  rounded  or  ovoid  body,  from  one-half  to  two  milli- 
metres in  diameter,  situated  partly  in  the  mucous  membrane  and  partly 
below  it.  It  consists  of  a  closed  capsule,  from  the  inner  surface  of 
which  slender  anastomosing  filaments  pass  through  the  substance  of 
the  organ,  forming  a  scaffolding  or  frame-work  of  minute  fibres.  In 
the  interstices  there  is  a  small  quantity  of  fluid,  together  with  an 
abundance  of  lymph  corpuscles,  or  faintly  granular  cells  about  13  mmm. 
in  diameter.  The  follicle  is  also  provided  with  capillary  blood-vessels, 
which  penetrate  its  investing  capsule,  inosculate  freely  in  its  interior, 
and  return  upon  themselves  in  loops  near  its  centre. 

These  follicles  have  a  close  relation  with  the  lymphatics  of  the  intes- 
tine. The  lymphatic  vessels  coming  from  the  villi  form  a  plexus  in  the 
substance  of  the  mucous  membrane,  from  which  branches  pass  to  the 
follicles  and  ramify  over  them,  forming  another  plexus  upon  their  in- 
vesting capsule.  They  do  not,  however,  penetrate  into  the  interior 
of  the  follicles,  which  are  occupied  by  blood-vessels  alone.  Owing  to 
the  analogy  in  structure  between  these  bodies  and  portions  of  the 
lymphatic  glands,  as  well  as  to  the  fact  that  the  lacteals  from  the  neigh- 
borhood of  Peyer's  patches  are  more  numerous  than  these  from  other 
points  of  the  intestine,  the  closed  follicles  are  generally  regarded  as 
belonging  to  the  system  of  the  lymphatic  glands.  They  furnish  no 
secretion  to  the  intestinal  cavity,  but  are  connected  in  some  way  with 
the  elaboration  of  the  absorbed  materials. 

Absorption  by  the  Villi. 

The  villi  are  the  active  agents  in  the  process  of  absorption.  The 
entire  mucous  membrane  of  the  small  intestine,  including  the  valvuhe 
conniventes,  represents  about  6000  square  centimetres  of  surface ;  and 
as  the  number  of  the  villi  is,  on  the  average,  not  less  than  30  to  the 
square  millimetre,  there  must  be  at  least  from  fifteen  to  twenty  millions 
of  them  in  the  intestine.  By  their  abundance,  as  well  as  by  their  pro- 
jecting form,  they  multiply  the  extent  of  contact  of  the  digested  fluids 
with  the  mucous  membrane,  and  increase,  to  a  corresponding  degree, 
the  activity  of  absorption.  They  hang  out  into  the  nutritious,  semi- 
fluid mass  in  the  intestinal  cavity,  as  the  roots  of  a  tree  penetrate  the 
soil ;  and  they  imbibe  its  liquefied  portions  with  a  rapidity  which  is  in 
proportion  to  their  extent  of  surface  and  the  movement  of  the  circu- 
lation. 

Absorption  is  also  hastened  by  the  peristaltic  action  of  the  intestine. 


ABSORPTION. 


197 


FIG.  38. 


The  muscular  layer  throughout  the  alimentary  canal  is  double,  consist- 
ing of  circular  and  longitudinal  fibres.     Their  action  may  be  excited 
in  the  recently  killed  animal,  by  pinching  the  exposed  intestine  with 
the  blades  of  a  forceps.    A  contraction  takes  place  at  the  spot  irritated, 
the  intestine  is  reduced  in  diameter,  and  its  contents  forced  onward! 
The  local  contraction  then  propagates  itself  to  the  neighboring  parts^ 
while  the  portion  originally  contracted  becomes  relaxed ;  and  a  slow' 
continuous,  creeping  motion  of  the  intestine  is  produced,  by  successive 
waves  of  contraction  and  relaxation,  following  each  other  from  above 
downward.     At  the  same  time  the  longitudinal  fibres  have  a  similar 
alternate  action,  drawing  the  narrowed  portions  of  intestine  up  and 
down,  as  they  successively  become  contracted  or  relaxed.     The  effect 
produced  is  a  peculiar,  writhing,  worm-like,  or  "  vermicular  "  motion, 
among  the   coils   of   intestine. 
During  life,  this  action  of  the 
intestine  is  excited  by  the  food 
undergoing  digestion.      By  its 
means   the  substances  passing 
from  the  stomach  into  the  duode- 
num are  made  to  traverse  the 
entire  length  of  the  small  intes- 
tine, and  brought  in  contact  suc- 
cessively with  the  whole  of  its 
mucous  membrane.   During  this 
passage  the   absorption  of  the 
digested  food  takes  place,  so  that 
its  liquefied  portions  disappear, 
and,  at   the  lower  end   of  the 
small  intestine,  there   remains 

only  the  undigested  part  of  the    CHYLE  FROM  COMMENCEMENT  OP  THORACIC  DUCT  ; 

food,  together  with  the   refuse 

of  the  intestinal  secretions.     These  pass  through  the  ileo-caecal  orifice 

into  the  large  intestine,  and  are  there  reduced  to  the  condition  of  feces. 

The  fluids  of  the  intestine  are  first  absorbed  by  the  epithelial  cells 
of  the  villi,  and  thence  transmitted  to  the  deeper  portions  of  the  tissue. 
This  passage  of  the  products  of  digestion  through  the  substance  of  the 
epithelial  cells  is  difficult  of  demonstration  for  homogeneous  liquids, 
but  it  may  be  seen  in  the  fatty  matters  of  the  chyle.  Chyle,  drawn 
either  from  the  lacteal  vessels  or  from  the  thoracic  duct,  presents  the 
same  appearance,  containing  fatty  matter  under  the  form  of  granules, 
which  vary  in  size  from  2.5  mmm.  downward,  and  which  have  the 
usual  characters  of  oil  in  a  state  of  minute  subdivision. 

The  emulsioned  fat  of  the  chyle  has  accordingly  passed  from  the 
cavity  of  the  intestine  into  that  of  the  lacteal  vessels.  Its  transmis- 
sion is  facilitated  by  the  alkaline  condition  of  the  blood  and  of  the 
intestinal  juices.  Oil  by  itself  is  non-diffusible.  If  a  fluid  containing 
oil  be  placed  on  one  side  of  an  animal  membrane,  and  pure  water  on 


198 


FUNCTIONS    OF    NUTRITION. 


the  other,  the  water  will  readily  penetrate  the  substance  of  the  mem- 
brane, while  the  oily  particles  cannot  be  made  to  pass  under  any  ordi- 
nary pressure.  But  though  this  be  true  for  pure  water,  it  is  not  true 
for  slightly  alkaline  fluids  like  the  serum  of  blood  or  the  lymph.  This 
was  shown  by  the  experiments  of  Matteucci,  with  an  oily  emulsion 
in  an  alkaline  fluid  containing  4.3  parts  of  potassium  hydrate  per  thou- 
sand. Such  a  solution  has  no  alkaline  taste,  and  its  action  on  reddened 
litmus-paper  is  about  equal  to  that  of  the  lymph  and  chyle.  If  such 
an  emulsion  be  placed  in  an  endosmometer,  together  with  a  watery 
alkaline  solution  of  similar  strength,  the  oily  particles  penetrate  the 
animal  membrane  without  much  difficulty,  and  mingle  with  the  exterior 
fluid.  Endosmosis  will  therefore  take  place  with  a  fatty  emulsion,  pro- 
vided the  fluids  be  slightly  alkaline  in  reaction. 

When  the  molecules  of  the  chyle  are  taken  up  by  the  villi,  their 


FIG.  39. 


FIG.  40. 


INTESTINAL  EPITHELIUM  ;  from  the  Dog 
while  fasting. 


INTESTINAL  EPITHELIUM  ;  from  the  Dog 
during  the  digestion  of  fat. 


passage  into  and  through  the  epithelial  layer  produces  a  marked  altera- 
tion in  the  appearance  of  its  cells.  In  the  intervals  of  digestion  these 
cells  are  nearly  transparent  and  homogeneous-looking,  presenting  under 
the  microscope  the  appearance  of  a  very  delicate  granulation.  (Fig. 
39.)  But  during  the  digestion  and  absorption  of  fatty  matters,  their 
substance  is  crowded  with  oily  particles.  (Fig.  40.)  The  oily  matter 
then  passes  onward,  penetrating  deeper  into  the  substance  of  the  villus, 
until  received  by  the  capillary  vessels  in  its  interior. 

Absorption  by  the  Blood-vessels. — The  final  absorption  of  the  digested 
fluids  is  accomplished  mainly  by  the  blood-vessels  of  the  intestinal 
villi.  Their  situation,  their  numbers,  and  the  rapid  movement  of  tin* 
blood,  are  all  favorable  conditions  for  the  performance  of  this  function. 
The  capillary  plexus  of  each  villus  is  situated  in  its  superficial  part,  im- 
mediately beneath  the  epithelium  cells,  so  that  the  absorbed  fluids,  after 


ABSORPTION.  199 

passing  through  the  epithelial  layer,  come  at  once  in  contact  with  the 
vascular  network.  The  extension  of  absorbing  surface,  from  the  division 
and  inosculation  of  these  vessels,  and  the  renovation  of  their  fluids  by 
the  movement  of  the  circulation,  provide  for  their  constant  activity, 
and  drain  away  the  absorbed  fluids  from  the  interior  of  the  villus  as 
fast  as  they  are  taken  up  by  its  surface. 

The  activity  of  the  blood-vessels  in  this  process  is  a  matter  of  direct 
observation.  It  was  first  shown  by  Magendie,*  who  found  that  the 
absorption  of  poisonous  substances  would  take  place,  in  the  living  ani- 
mal, both  from  the  cavity  of  the  intestine  and  from  the  tissues  of  the 
leg,  notwithstanding  that  all  communication  Jhrough  the  lacteals  and 
lymphatics  was  cut  off,  and  the  blood-vessels  alone  remained.  These 
results  were  corroborated  by  Panizza,  who  succeeded  in  detecting  the 
substances  absorbed  in  the  venous  blood  returning  from  the  part.  This 
observer,  after  having  opened  the  abdomen  of  a  horse,  drew  out  a  fold 
of  the  small  intestine,  about  20  centimetres  in  length,  which  he  included 
between  two  ligatures.  A  ligature  was  then  placed  upon  the  mesenteric 

FIG.  41. 


CAPILLARY  BLOOD-VESSELS  OF  THE  INTESTINAL  VILLI  ;  from  the  Mouse.    (Kolliker.) 

vein  receiving  the  blood  from  this  portion  of  intestine ;  and,  in  order 
that  the  circulation  might  not  be  interrupted,  an  opening  was  made  in 
the  vein  behind  the  ligature,  so  that  the  blood  brought  by  the  mesen- 
teric artery,  after  circulating  in  the  intestinal  capillaries,  passed  out 
at  the  opening,  and  was  collected  for  examination.  Hydrocyanic  acid 
was  then  introduced  into  the  intestine,  and  almost  immediately  after- 
ward its  presence  was  detected  in  the  blood  flowing  from  the  venous 
orifice.  The  animal,  however,  was  not  poisoned,  since  the  acid  was 
prevented  by  the  ligature  from  gaining  an  entrance  into  the  general 
circulation. 

Panizza  afterward  varied  this  experiment  in  the  following  manner : 
Instead  of  tying  the  mesenteric  vein,  he  simply  compressed  it.  Hydro- 
cyanic acid  being  then  introduced  into  the  intestine,  no  effect  was  pro- 
duced so  long  as  the  vein  remained  compressed ;  but  as  soon  as  the 

*  Journal  de  Physiologic.     Paris,  1825,  toine  i.,  p.  18. 


200  FUNCTIONS    OF    NUTRITION. 

blood  was  again  allowed  to  pass,  symptoms  of  general  poisoning  were 
manifest.  Lastly,  in  a  third  experiment,  he  removed  the  nerves  and 
lacteal  vessels  supplying  the  intestinal  fold,  leaving  the  blood-vessel- 
untouched.  Hydrocyanic  acid,  introduced  into  the  intestine,  found  an 
immediate  entrance  into  the  general  circulation,  and  the  animal  was  at 
once  poisoned.  The  blood-vessels,  therefore,  are  not  only  capable  of 
absorbing  fluids  from  the  intestine,  but  may  take  them  up  even  more 
rapidly  than  the  lacteals. 

The  entrance  of  digested  materials  into  the  blood-vessels  of  the  intes- 
tine is  demonstrated  in  a  similar  way.  After  the  digestion  of  food 
containing  albuminous  and  starchy  ingredients,  both  glucose  and  pep- 
tone are  met  with  in  the  blood  of  the  portal  vein.  Emulsioned  fatty 
matters  may  also  be  followed,  in  their  passage  through  the  same  chan- 
nels, by  the  chylous  aspect  which  the}7"  communicate  to  the  portal  blood. 
The  blood  of  the  portal  system,  in  carnivorous  animals,  during  diges- 
tion, contains  fatty  matter  in  a  state  of  minute  subdivision,  similar  in 
appearance  to  that  found  in  the  chyle  and  in  the  villi ;  and  these  ingre- 
dients are  often  so  abundant  as  to  cause  a  turbid  appearance  in  the  serum 
after  coagulation.  A  variety  of  observers  (Lehmann,  Schultz,  Simon), 
in  examining  the  blood  from  different  parts  of  the  body,  have  also 
found  the  blood  of  the  portal  system  considerably  richer  in  fat  than  that 
of  the  arteries  or  of  other  veins,  particularly  while  digestion  is  going  on. 

Absorption  by  the  Lacteals. — The  absorption  of  digested  materials, 
particularly  of  the  fatty  matters,  is  also  accomplished  by  the  lacteals 
of  the  small  intestine.  These  vessels  are  part  of  the  great  lymphatic 
system,  which  is  distributed  everywhere  in  the  integuments  of  the 
head,  the  parietes  of  the  trunk,  the  limbs,  and  in  the  glands,  muscles, 
and  mucous  membranes  throughout  the  body.  Originating  in  the  tis- 
sues of  these  organs,  they  pass  from  the'  periphery  toward  the  centre, 
converging  and  uniting  with  each  other  like  the  veins,  and  passing,  at 
various  points,  through  the  lymphatic  glands. 

The  fluid  generally  contained  in  these  vessels  is  the  "  lymph."  It  is 
a  colorless  or  slightly  yellowish  transparent  liquid,  absorbed  by  the 
lymphatic  vessels  from  the  various  tissues,  and  containing,  beside  water 
and  saline  matters,  a  small  quantity  of  fibrine  and  albumen. 

The  lymphatic  vessels  of  the  intestine  originate  in  the  villi,  as  longi- 
tudinal spaces  lined  with  flattened  epithelium  cells,  becoming  provided, 
after  a  short  distance,  with  transparent,  elastic  coats,  like  those  of  the 
capillary  blood-vessels.  On  emerging  from  the  villi  they  become  part 
of  the  lymphatic  plexus,  from  which  the  main  branches  pass  between 
the  layers  of  the  mesentery,  from  the  intestine  toward  the  posterior 
part  of  the  abdomen.  In  this  part  of  their  course  they  inosculate  with 
each  other  by  transverse  branches,  and  pass  through  several  ranges  of 
mesenteric  glands,  representing  the  lymphatic  glands  of  the  abdominal 
cavity.  Near  the  attached  portion  of  the  mesentery,  on  the  right  side 
of  the  abdomen,  about  the  level  of  the  second  lumbar  vertebra,  they 
terminal*1  in  a  saecular  dilatation,  the  "receptaculum  chyli."  From  this 


ABSORPTION. 


201 


point  the  thoracic  duct  passes  upward  through  the  chest,  crossing 
obliquely  from  right  to  left,  and  terminating  in  the  left  subclavian  vein, 
at  its  junction  with  the  jugular  of  the  same  side. 

In  the  intervals  of  digestion  the  fluid  contained  in  the  lymphatic 
vessels  is  everywhere  the  same  in  appearance.  Its  colorless  and  trans- 
parent character,  the  small  size  of  the  vessels,  and  the  thinness  and 
delicacy  of  their  coats,  make  them  nearly  or  quite  invisible  to  the  unaided 
eye.  But  during  the  absorption  of  food  the  lymphatics  of  the  small 
intestine  are  distended  with  chyle,  and  thus  become  visible  as  opaque 
white  filaments,  ramifying  in  the 
intestinal  walls,  converging  from 
the  intestine  to  the  receptaculum 
chyli,  and  contrasting  strongly 
with  the  semi-transparent  ruddy 
color  of  the  neighboring  tissues. 
Owing  to  the  appearance  thus 
given  to  the  vessels  by  the  milky 
fluid  which  they  contain,  they 
have  received  the  name  of  the 
lacteals,  or  lactiferous  vessels  of 
the  abdomen. 

The  presence  of  chyle  in  the 
lacteals  is,  therefore,  only  peri- 
odical. The  fatty  substances  be- 
gin to  be  absorbed  during  diges- 
tion, as  soon  as  they  have  been 
emulsionedby  the  digestive  fluids. 
As  the  process  goes  on,  they  ac- 
cumulate in  larger  quantity,  and 
gradually  fill  the  whole  lacteal 
system  of  the  abdomen.  But  as 
digestion  and  absorption  come  to 
an  end,  the  milky  fluid  disappears 
from  these  vessels,  and  they  re- 
sume their  former  transparent 
appearance. 

The  lacteals,  accordingly,  are 
the  lymphatics  of  the  small  intes- 
tine, which,  in  addition  to  the 
lymph  which  they  usually  con- 
tain, have  absorbed  a  fluid  rich 
in  cnmlsioned  fat.  They  are  then 
distinguished  from  the  lymphatics 
elsewhere  by  the  milky  character  of  their  contents,  which  accumulate 
in  the  receptaculum  chyli,  and  may  be  followed  thence  through  the 
thoracic  duct,  to  its  termination  in  the  subclavian  vein.  (Fig.  42.) 

It  was  owing  to  the  opacity  of  the  lacteals  during  digestion  that 


LACTEALS  AND  LYMPHATICS,  during  digestion. 


202  FUNCTIONS    OF    NUTRITION. 

these  vessels  were  discovered  in  1622  by  Asellius,  who  first  saw  them 
on  opening  the  abdomen  of  a  dog,'  a  few  hours  after  the  ingestion 
of  food.  The  discovery  of  the  general  lymphatic  system  was  made 
subsequently  by  Rudbeck  and  Bartholin,  in  1651  and  1653,  and 
was  consequent  upon  the  previous  observations  on  the  lacteals  of  the 
abdomen. 

That  the  white  color  of  the  chyle  during  digestion  is  really  due  to 
the  presence  of  fatty  substances  absorbed  from  the  intestine,  is  shown 
by  the  fact  that  its  intensity  is  in  proportion  to  the  quantity  of  fat 
in  the  food.  It  is  generally  less  marked  in  herbivorous  than  in  carn- 
ivorous animals.  According  to  the  observations  of  Tiedemann  and 
Gmelin,  in  a  dog  fed  with  fatty  matters  the  lacteals  are  abundantly 
filled  with  an  opaque  white  fluid,  while  in  the  same  animal  fed  with 
starchy  matters  alone,  the  chyle  is  pale  and  but  slightly  opaline ;  and 
Bernard  has  shown  that  if,  in  a  dog  after  several  days'  fasting,  a  little 
ether,  containing  fat  in  solution,  be  injected  into  the  stomach,  without 
the  introduction  of  other  food,  at  the  end  of  a  few  hours  the  lacteals 
are  fully  distended  with  chyle,  similar  in  appearance  to  that  seen  during 
ordinary  digestion. 

Passage  of  Absorbed  Materials  into  the  General  Circulation. 

The  products  of  digestion,  taken  up  by  the  blood-vessels  and  lym- 
phatics of  the  intestine,  pass  by  two  different  routes  into  the  general 
circulation.  The  blood  of  the  portal  vein,  containing  peptone,  glucose, 
and  molecular  fat,  is  carried  to  the  liver,  where  it  traverses  the  capil- 
lary vessels  of  this  organ  before  reaching  the  vena  cava  and  the 
right  side  of  the  heart.  The  chyle,  on  the  other  hand,  containing 
a  large  proportion  of  fatty  ingredients,  passes  by  the  thoracic  duct  to 
the  left  subclavian  vein,  and  there  mingles  with  the  returning  current 
of  the  venous  blood.  But  all  these  substances,  after  entering  the  cir- 
culation and  coming  in  contact  with  the  blood,  are  so  modified  as  no 
longer  to  be  recognizable  in  their  original  form.  This  change  takes 
place  very  rapidly  with  peptone  and  glucose.  Peptone  passes,  in  all 
probability,  into  the  condition  of  albumen ;  while  the  glucose  is  for  the 
most  part  deposited  in  the  liver  in  an  insoluble  form,  those  portions 
which  reach  the  general  circulation  being  decomposed  or  transformed, 
and  thus  losing  their  characteristic  properties.  The  fatty  matters 
also  undergo  a  transformation  while  passing  through  the  lungs  by 
which  their  distinctive  characters  are  destroyed,  and  they  are  no  longer 
visible  as  oleaginous  particles.  This  alteration  is  so  complete,  during 
the  early  part  of  digestion,  or  when  the  proportion  of  fat  in  the  food 
is  small,  that  all  the  oleaginous  master  disappears  in  the  lungs,  and 
none  is  to  be  detected  in  the  general  circulation. 

But  as  digestion  proceeds,  especially  with  food  abundant  in  oleaginous 
substances,  an  increasing  quantity  of  fat  finds  its  way  into  the  blood, 
and  a  time  arrives  when  the  whole  of  it  is  not  destroyed  during  its 
passage  through  the  lungs.  Its  absorption  then  taking  place  more 


ABSORPTION.  203 

rapidly  than  its  decomposition,  it  begins  to  appear,  in  moderate 
quantity,  in  the  general  circulation ;  and,  lastly,  when  absorption  is 
at  the  point  of  greatest  activity,  it  is  found  in  considerable  abundance 
throughout  the  vascular  system.  At  this  period,  some  hours  after  the 
ingestion  of  food  rich  in  oleaginous  matters,  the  blood,  not  only  of  the 
portal  vein,  but  also  of  the  general  circulation,  contains  a  superabun- 
dance of  molecular  fat,  derived  from  the  digestive  process.  Blood  drawn 
at  that  time,  from  the  veins  or  the  arteries  in  any  part  of  the  body,  will 
present  the  appearance  known  as  that  of  "  chylous  "  or  "  milky  "  blood. 
On  the  separation  of  the  clot  the  serum  is  turbid ;  and  after  a  few  hours 
of  repose,  its  fatty  ingredients  rise  to  the  surface  in  an  opaque,  creamy- 
looking  pellicle.  This  appearance  has  been  sometimes  observed  in 
human  blood,  in  cases  of  sudden  death  after  a  full  meal.  It  is  a  purely 
normal  phenomenon,  due  to  the  rapid  absorption,  at  certain  periods 
during  digestion,  of  oleaginous  substances  from  the  intestine.  It  can 
be  observed  at  any  time  in  the  dog  by  feeding  him  with  fat  meat,  and 
drawing  blood,  seven  or  eight  hours  afterward,  from  the  carotid  artery 
or  the  jugular  vein. 

This  condition  lasts  for  a  varying  time,  according  to  the  amount  of 
oleaginous  matter  in  the  food.  When  digestion  is  terminated,  and  fat 
ceases  to  be  absorbed,  its  transformation  continuing  to  take  place  in 
the  blood,  it  gradually  disappears  from  the  vascular  system ;  and, 
finally,  when  the  whole  of  it  has  been  disposed  of  by  the  nutritive 
process,  the  serum  again  becomes  transparent,  and  the  blood  returns  to 
its  ordinary  condition. 

In  this  manner  the  nutritive  elements  of  the  food,  prepared  by  the 
digestive  process,  are  taken  into  the  circulation  under  the  forms  of 
peptone,  glucose,  and  chyle,  and  accumulate  as  such  at  certain  times  in 
the  blood.  But  these  conditions  are  temporary  and  transitional.  The 
absorbed  materials  soon  pass  into  other  forms,  and  become  assimilated 
to  the  preexisting  elements  of  the  circulating  fluid,  thus  accomplishing 
finally  the  object  of  digestion,  and  replenishing  the  blood  with  its 
nutritive  elements. 

Absorption  of  Carbohydrates  and  Production  of  Glycqgen 
in  the  Liver. 

The  absorption  of  starchy  and  saccharine  matters,  and  the  changes 
which  they  undergo  while  passing  through  the  liver  to  the  general  cir- 
culation, have  been  the  subject  of  extended  observations,  and  require 
a  special  description.  They  are  connected  with  the  production  of 
glycogen  in  the  liver,  as  well  as  with  its  transformation  and  disappear- 
ance. 

If  the  liver  of  a  carnivorous  or  herbivorous  animal,  after  twenty- 
four  hours'  fasting,  be  taken  from  the  body  immediately  after  death, 
finely  divided,  and  boiled  for  a  few  moments  in  water  with  animal 
charcoal  or  an  excess  of  sodium  sulphate,  to  eliminate  the  albuminous 
and  coloring  matters,  the  filtered  fluid  will  be  nearly  clear,  or  will  show 


204  FUNCTIONS    OF    NUTRITION. 

only  a  moderately  opaline  tinge.  But  if  the  same  thing  be  done 
within  a  few  hours  after  feeding,  the  watery  decoction  of  the  liver 
will  be  strongly  opalescent;  containing  in  considerable  quantity  a 
matter  which  communicates  to  the  solution  a  partial  turbidity.  This 
matter  is  glycogen,  which  is  present  in  varying  quantity  under  these 
two  conditions. 

Origin  and  Formation  of  Glycogen. — As  this  substance  is  present 
in  the  liver  tissue  of  both  carnivorous  and  herbivorous  animals,  it  may 
be  derived  from  the  materials  of  either  kind  of  food.  In  the  carnivora, 
at  least,  there  is  evidence  that  it  is  supplied  from  nitrogenous  materials, 
by  the  nutritive  changes  which  they  undergo  in  the  liver.  Under  some 
circumstances  a  material  resembling  glycogen,  or  identical  with  it,  may 
be  present  in  the  muscles  of  the  herbivora.  Bernard  has  found  it  in 
the  muscular  tissue  in  rabbits,  and  especially  in  pigeons,  when  fed  on 
the  cereal  grains,  and  in  horses  kept  on  oats  and  barley ;  but  in  all 
these  animals  it  disappears  when  the  food  is  changed,  or  after  some 
days'  fasting.  Luchsinger*  has  also  found  it  absent  from  the  muscles 
of  the  rabbit  after  several  days'  fasting,  but  more  persistent  in  the 
pectoral  muscles  of  the  fowl  under  similar  conditions. 

It  is  accordingly  not  a  constant  but  only  an  occasional  ingredient  of 
muscular  flesh,  and  when  present  is  usually  in  very  small  quantity. 
Poggiale,^  in  many  experiments  instituted  for  this  purpose  by  a 
Commission  of  the  French  Academy  of  Sciences,  found  glycogen  in 
ordinary  butcher's  meat  only  once.  We  have  also  found  it  absent 
from  the  fresh  meat  of  the  bullock's  heart,  when  examined  in  the 
manner  above  described.  Nevertheless,  in  dogs  fed  exclusively  for 
eight  days  on  this  food,  glycogen  may  be  abundant  in  the  liver, 
while  it  does  not  exist  in  other  internal  organs,  as  the  spleen,  lungs, 
and  kidneys. 

Glycogen  is  produced  in  the  liver  in  especial  abundance,  after  the  in- 
gestion  of  starchy  and  saccharine  food.  Bernard  J  found  the  decoction 
of  the  liver  tissue  in  dogs,  after  feeding  for  two  days  with  bread  and 
starch  paste,  very  turbid  and  milky  in  appearance.  Subsequent  ex- 
periments by  the  same  observer  §  have  shown  that  a  starchy  diet 
augments  notably  the  quantity  of  glycogen  in  the  liver.  This  fact  was 
first  demonstrated  in  a  special  manner  by  the  observations  of  Pavy,|| 
who,  by  comparative  experiments  on  dogs  fed  with  animal  and  vege- 
table food,  found  that  the  influence  of  the  latter  was  to  increase 
decidedly  the  weight  of  the  liver,  and  also  the  percentage  of  glycogen 
which  it  contained.  The  same  effect  was  produced  by  a  diet  of  animal 
food  and  sugar.  The  following  table  gives  the  average  results  of  three 
series  of  observations  by  Pavy : 

*  Archiv  fur  die  gesammte  Physiologic.     Bonn,  1873,  Band  viii.,  p.  290. 

f  Journal  de  la  Physiologic.     Paris,  1858,  p.  558. 

J  Le£ons  de  Physiologic  Expe>imentale.    Paris,  1855,  p.  159. 

$  Revue  des  Sciences  Me"dicales.     Paris,  1874,  tome  Hi.,  p.  34. 

||  Nature  and  Treatment  of  Diabetes.     London,  1862. 


ABSORPTION.  205 

PRODUCTION  OF  GLYCOGEN,  IN  DOGS,  UNDER  VARYING  DIET. 

Diet  for                                                  Weight  of  liver,  Glycogen  in  the 

several  days                                             in  percentage  of  fresh  liver, 

previously.                                                bodily  weight.  per  cent. 

Tripe 3.03  7.19 

Tripe  and  sugar    ....         6.42  14.50 

Meal,  bread,  potatoes    .         .         .         6.06  17.23 

Experiments  on  the  rabbit  also  showed  that  in  this  animal  both  the 
weight  of  the  liver  and  its  percentage  in  glycogen  are  much  diminished 
by  fasting,  but  are  maintained  at  the  maximum  standard,  for  a  time  at 
least,  by  an  exclusive  diet  of  carbohydrates.  The  average  results  were 
as  follows : 

AVEEAGE  PRODUCTION  OF  GLYCOGEN  IN  KABBITS,  WHEN  FASTING  AND  WHEN 
FED  ON  CARBOHYDRATES. 

Diet  for  three                                         Absolute  weight  of  Glycogen  in  the  fresh 

days  previously.                                       liver  (grammes).  liver  (per  cent.). 

No  food 34.02  1.35 

Starch  and  sugar         .         .         .         73.71  16.15 

The  quantity  of  glycogen  found  in  the  liver  by  Pavy  is  greater  than 
that  obtained  by  subsequent  observers  under  similar  circumstances ;  but 
the  fact  of  the  increase  of  glycogen  under  the  use  of  carbohydrates  has 
been  confirmed  by  other  experimenters.  Dock  *  found,  in  experiments 
on  the  rabbit,  that  after  from  3  to  5  days'  fasting  the  glycogen  in  the 
liver  was  reduced  to  a  very  minute  quantity,  or  more  frequently  was 
entirely  absent.  But  if,  in  this  condition,  a  solution  of  glucose  were 
introduced  into  the  stomach  through  a  catheter,  and  the  animal  killed 
from  19  to  24  hours  afterward,  the  glycogen  in  the  liver  amounted  to 
from  0.650  to  1.243  grammes.  After  even  7  days'  fasting,  followed  by 
an  injection  of  glucose  into  the  stomach,  so  short  a  time  as  four  hours 
was  sufficient  to  produce  an  abundance  of  glycogen  in  the  liver.  The 
deposit  of  this  substance  accordingly  takes  place  so  rapidly  after  the 
ingestion  of  this  kind  of  food,  that  no  doubt  can  remain  of  its  being 
produced  from  saccharine  or  starchy  substances. 

Tscherinow  f  showed,  by  his  observations  on  fowls,  both  the  produc- 
tion of  glycogen  from  animal  food,  and  its  more  abundant  deposit  under 
a  vegetable  diet.  He  found,  in  this  species,  two  days'  fasting  sufficient 
to  reduce  the  glycogen  to  a  minimum.  After  a  preliminary  fast  of  this 
duration,  the  fowls  were  fed  for  two  or  three  days  with  different  kinds  of 
food,  and  then  killed  and  examined.  The  average  results  were  as  follows : 

PRODUCTION  OF  GLYCOGEN  IN  FOWLS  UNDER  DIFFERENT  KINDS  OF  DIET. 
Diet  previous  to  the  Glycogen  in  the  frersh 

experiment.  liver,  per  cent. 

Fasting,  2  days 0.57 

Lean  meat,  2  to  4  days 1.40 

Barley,  2  days 5.41 

Eice,  2  days V.21 

Fibrine  and  sugar,  2  to  3  days 10.20 


*  Archiv  fur  die  gesammte  Physiologic.     Bonn,  1872,  Band  v.,  p.  571. 
f  Archiv  fur   pathologische  Anatomie   und   Physiologic.      Berlin,  1869,  Band 
xlvii.,  p.  102. 


206  FUNCTIONS    OF    NUTRITION. 

It  appears  furthermore  from  the  experiments  of  Weiss  and  Luch- 
singer*  that  a  similar  increase  of  glycogen  will  take  place  in  the  liver 
after  the  ingestion  of  glycerine  (C3HH03),  but  not  under  the  use  of  fat 
or  of  the  alkaline  tartrates  or  lactates. 

There  is  accordingly  every  reason  to  believe  that  carbohydrates,  when 
taken  with  the  food,  are  transported  to  the  liver  by  the  portal  circula- 
tion, and  fixed  in  its  substance  under  the  form  of  glycogen.  It  makes 
no  difference,  in  this  respect,  whether  they  be  taken  as  starch  or  as 
sugar ;  since  starchy  matters  are  transformed  into  glucose  by  digestion 
in  the  intestine.  It  is  under  the  form  of  glucose,  therefore,  that  they 
enter  the  portal  circulation  and  reach  the  tissue  of  the  liver.  The  con- 
version* of  this  substance  into  glycogen,  as  shown  in  a  former  chapter 
(page  61),  is  essentially  a  dehydration.  It  is  not  possible  to  say  in 
what  manner  or  by  what  influence  this  change  takes  place ;  but  it  is 
one  of  the  simplest  methods  of  transformation  for  organic  substances, 
and  exactly  the  reverse  of  that  by  which  glucose  is  produced  from  starch 
in  the  intestine. 

Transformation  of  Glycogen  into  Glucose. — The  glycogen  thus  de- 
posited in  the  liver  from  the  products  of  digestion  does  not  remain  under 
that  form  in  the  hepatic  tissue.  It  is  gradually  reconverted  into  glucose, 
and  carried  away  into  the  general  circulation.  This  is  shown  by  the 
fact  that  the  liver  always  contains  a  small  quantity  of  glucose,  even  in 
the  intervals  of  digestion,  though  none  may  be  present  in  the  blood  of 
the  portal  vein ;  and  that  the  blood  generally  contains  about  the  same 
quantity  of  glucose,  though  the  supply  of  carbohydrates  in  the  food  be 
temporarily  suspended.  The  first  fact  was  discovered  by  Bernard  f  in 
1848.  If  a  dog,  cat,  or  other  carnivorous  animal  be  killed  after  several 
days  of  an  exclusive  meat  diet,  the  liver  alone  of  all  the  internal  organs 
is  found  to  contain  glucose.  The  hepatic  tissue,  ground  to  a  pulp  and 
boiled  in  a  little  water  with  an  excess  of  sodium  sulphate,  to  eliminate 
the  albuminous  and  coloring  matters,  will  yield  a  filtered  extract  which 
responds  to  Trommer's  or  Fehling's  test,  and  enters  into  fermentation 
on  the  addition  of  yeast.  At  the  same  time  neither  the  contents  of  the 
intestine,  the  blood  of  the  portal  vein,  nor  any  other  of  the  solid  organs 
give  evidence  of  a  similar  ingredient.  By  the  use  of  Fehling's  test  the 
proportion  of  saccharine  matter  in  the  liver  substance  may  be  deter- 
mined. 

The  presence  of  glucose  in  the  liver  under  these  circumstances  is 
common  to  all  animals  so  far  as  known.  It  has  been  found  by  Bernard 
in  the  monkey,  dog,  cat,  rabbit,  horse,  ox,  sheep,  birds,  reptiles,  and  sev- 
eral fish.  If  the  fresh  liver  of  man  be  examined  after  sudden  death  by 
accident  or  violence,  it  is  also  found  to  contain  sugar. 

The  glucose  thus  produced  in  the  liver  originates  by  transformation 
from  the  hepatic  glycogen  under  the  influence  of  a  ferment.  As  the 

*  Arcliiv  fur  die  gesammte  Physiologic,  1873,  Band  viii.,  p.  290. 

fComptes  Rendus  de  1' Academic  drs  Sciences.     Paris,  1850,  tome  xxxi.,  p.  571. 


ABSORPTION.  207 

organ  usually  contains  a  store  of  glycogen  derived  from  the  last  diges- 
tive process,  the  conversion  of  this  substance  into  glucose  will  go  on  after 
death,  and  even  in  the  separated  liver,  at  the  temperature  of  38°  C. 
If  the  liver  of  a  healthy  dog  be  taken  out  immediately  after  death  and 
injected  with  water  by  the  portal  vein,  the  fluid  which  escapes  by  the 
hepatic  vein,  after  traversing  the  liver  tissue,  contains  sugar.  But  as 
the  injection  is  continued,  the  quantity  of  glucose  extracted  by  it  from 
the  liver  grows  constantly  less ;  until  in  from  half  an  hour  to  an  hour 
it  is  completely  exhausted,  and  neither  the  injected  fluid  nor  the  hepatic 
tissue  contains  any  further  trace  of  glucose.  If  such  a  liver  be  kept  in 
a  moderately  warm  place  for  some  hours  its  tissue  will  again  become 
saccharine.  Its  glucose  may  be  exhausted  by  a  fresh  injection,  and  again 
reproduced  until  all  the  glycogen  has  been  transformed,  or  until  decom- 
position begins  to  be  established.  The  glycogen,  being  less  soluble  than 
sugar,  remains  behind  after  such  an  injection  and  produces  a  new  supply 
of  glucose  by  a  new  transformation. 

After  death,  accordingly,  if  the  liver  be  allowed  to  remain  saturated 
with  its  natural  juices,  this  transformation  goes  on  for  a  time,  and  the 
glucose  of  the  hepatic  tissue  increases  at  the  expense  of  its  glycogen. 
This  fact  is  established  by  the  experience  of  all  observers.  According 
to  our  own  observations  on  the  dog,  the  glucose  in  the  liver  is  increased 
within  an  hour  after  death  to  four  or  five  times  its  former  quantity. 
Afterward  the  change  goes  on  more  slowly,  its  rate  diminishing  with 
the  lapse  of  time,  so  that  at  the  end  of  twelve  hours  the  sugar  may 
hardly  exceed  five  or  six  times  its  original  amount.  The  following 
table  gives  the  result  of  three  experiments  in  this  direction : 

PROPORTION  OF  GLUCOSE  IN  THE  LIVER  qp  THE  DOG  AT  DIFFERENT  PERIODS 

AFTER  DEATH. 
At  the  end  of  Per  thousand  parts. 

f   5  seconds 810 

No.  1.   -j  15  minutes 792 

I    1  hour  10.260 

No  2    1    5  seconds 3-850 

'    1    6  hours 11.458 

4  seconds       ......  2.675 

,    Ihour 11.888 

3'  <    4  hours 13.361 

12  hours 15.351 

It  has  been  denied  by  some  writers  (Pavy,  Meissner,  RHter,  Schiff) 
that  glucose  exists  in  the  liver  during  life ;  the  whole  of  it  being  con- 
sidered as  the  product  of  a  change  after  death.  But  there  is  abundant 
evidence  of  its  existence  at  the  moment  of  death,  or  when  pieces  of  the 
hepatic  substance  are  excised  from  the  living  animal ;  and  even  its 
quantity  under  these  circumstances  is  nearly  uniform,  varying  from 
about  2  to  4  parts  per  thousand  of  the  liver  tissue.  Harley,*  who 

*  Proceedings  of  the  Eoyal  Society  of  London,  1860,  vol.  x.,  p.  289. 


208  FUNCTIONS    OF    NUTRITION. 

killed  the  animal  by  section  of  the  medulla  oblongata,  immediately 
placing  a  portion  of  the  liver  in  a  freezing  mixture,  and  afterward 
slicing  it  into  boiling  acidulated  water,  has  shown  that  glucose  may  be 
demonstrated  in  the  organ  within  20  seconds  after  death.  If  a  portion 
of  the  liver,  separated  while  the  circulation  is  going  on,  be  ground  to  a 
pulp  and  plunged  into  strong  alcohol  or  boiling  water,  either  of  which 
arrests  the  transformation  of  glycogen,  its  decolorized  extract  will  give 
the  reaction  of  glucose  by  Fehling's  test.  We  have  invariably  obtained 
this  result  in  experiments  of  this  kind,*  though  the  time  occupied  in 
taking  out  the  liver  tissue  and  immersing  it  in  alcohol  or  boiling  water 
was,  on  the  average,  but  little  over  six  seconds.  Bernard,  f  in  a  re- 
examination  of  the  subject  after  a  long  interval,  found  that  in  dogs  and 
rabbits  pieces  of  the  liver,  cut  out  and  plunged  into  boiling  water  for 
two  or  three  seconds,  constantly  contained  glucose  in  nearly  the  above 
proportions ;  and  the  same  conclusion  has  been  reached  by  Seegen  and 
Kratschmer  J  in  experiments  on  dogs,  cats,  and  rabbits,  in  which  the 
time  varied  from  a  few  seconds  to  three  minutes.  It  appears,  therefore, 
that  glucose  is  a  normal  ingredient  of  the  liver  tissue  during  life. 

Absorption  and  Disappearance  of  the  Liver-sugar. — The  glucose 
produced  in  the  liver  from  the  transformation  of  glycogen  does  not. 
remain  at  the  place  of  its  formation.  It  is  absorbed  by  the  blood 
traversing  the  capillaries  of  the  organ,  and  carried  away  in  the  current 
of  the  circulation.  This  is  shown  by  the  fact  that  the  blood  of  the 
hepatic  vein,  as  well  as  the  liver  tissue,  contains  glucose,  although 
there  may  be  none  in  the  portal  blood  by  which  the  organ  is  supplied. 
As  the  blood,  before  its  entrance  into  the  liver,  in  these  cases,  is  desti- 
tute of  sugar,  and  yet  contains  this  substance  after  its  passage,  it  must 
acquire  its  saccharine  ingredient  in  the  liver  itself.  Bernard  §  has  shown 
that  if  two  specimens,  one  of  portal  and  one  of  hepatic  blood,  be  taken 
from  the  same  dog,  when  fasting  or  after  an  exclusive  diet  of  animal 
food,  the  former  will  show  no  trace  of  sugar,  while  the  latter  will  be 
saccharine.  Lehmann  ||  obtained  similar  results  in  dogs  and  horses. 

Glucose,  accordingly,  although  constantly  produced  in  the  liver,  does 
not  accumulate  in  the  organ  during  life  beyond  a  very  moderate  quan- 
tity. It  is  only  after  death,  when  the  circulation  has  come  to  un  end, 
and  while  tho  transformation  of  glycogen  is  still  going  on,  that  the 
proportion  of  glucose  in  the  liver  tissue  becomes  notably  increased. 
The  circulation  of  blood,  so  long  as  it  continues,  acts  like  an  injection 
through  the  hepatic  vessels,  and  extracts  from  the  organ  the  sugar  pro- 
duced at  the  expense  of  its  glycogen. 

In  this  way  the  blood  of  the  general  circulation  is  supplied  \\1th 

*  Transactions  of  the  New  York  Academy  of  Medicine,  1871.  2d  Series,  Vol  I., 
p.  28. 

f  Comptes  Rendus  de  PAcade"mie  des  Sciences.     Paris,  1877,  tome  Ixxxiv.,  p.  1201. 
J  Archiv  fur  die  gesamrate  Physiologic.     Bonn,  1880,  Band  xxii.,  p.  *J14. 
$  Le9ons  de  Physiologic  Expftimentale.     Paris,  185"),  pp.  'Jfi5,  469. 
||  Comptes  Rendus  de  FAcade'mie  des  Sciences.     Paris,  1855,  tome  xl.,  p.  585. 


ABSORPTION.  209 

glucose  from  the  liver.  According  to  the  more  recent  investigations 
of  Bernard,*  the  arterial  blood  of  both  herbivorous  and  carnivorous 
animals,  either  fasting  or  in  digestion,  and  that  of  man,  living  on  a 
mixed  diet,  always  contains  glucose  in  sensibly  the  same  proportion ; 
namely,  from  1.10  to  1.45  per  thousand  parts.  In  its  passage  through 
the  general  capillary  circulation,  the  glucose  disappears.  The  precise 
changes  which  it  undergoes,  and  the  immediate  products  of  its  decom- 
position, are  still  unknown,  but  they  no  doubt  serve  in  some  way  for 
the  process  of  general  nutrition.  Consequently  the  venous  blood  re- 
turning from  the  peripheral  organs  contains  less  glucose  than  the  arte- 
rial blood  with  which  they  are  supplied.  In  two  instances  Bernard 
found  in  the  dog  its  proportion,  in  the  blood  of  the  carotid  artery  and 
jugular  vein,  as  follows : 

PROPORTION  OF  GLUCOSE  IN  THE  BLOOD. 
From  the  Per  thousand  parts. 

Carotid  artery 1.14        1.23 

Jugular  vein 0.98        0.81 

In  the  venous  blood  of  the  trunk  and  lower  extremities  the  same 
diminution  occurs ;  but  at  the  level  of  the  hepatic  veins  the  quantity 
of  glucose  in  the  blood  suddenly  augments  to  more  than  double,  rising 
sometimes  to  a  maximum  of  2.50  or  3.00  parts  per  thousand.  This 
proportion  is  again  diminished  on  its  being  mingled  with  the  blood  of 
the  superior  vena  cava,  and  in  the  right  ventricle  the  maximum  is  1,81 
per  thousand  parts. 

So  far,  therefore,  we  must  regard  the  liver  as  a  temporary  deposit 
for  the  carbohydrates  in  the  form  of  glycogen.  According  to  this  view, 
the  system  requires  for  its  nutrition  a  constant  supply  of  glucose,  to 
be  decomposed  in  the  general  circulation.  The  starchy  matters  of  the 
food,  at  each  period  of  digestion,  are  rapidly  converted  into  soluble 
glucose,  and  absorbed  from  the  intestine  by  the  portal  blood.  On 
reaching  the  liver  they  are  reduced  to  the  dehydrated  or  glycogenic 
condition,  under  which  form  they  remain  as  a  reserve  material  until 
a  further  supply  shall  be  received  from  the  food.  During  this  interval, 
the  glycogen  is  slowly  reconverted  into  glucose,  and  given  up,  little 
by  little,  to  the  blood  of  the  general  circulation,  to  be  decomposed  in 
the  system  at  large.  The  proportion  of  glucose  in  the  blood  is  thus 
maintained  at  nearly  a  constant  standard,  notwithstanding  the  varia- 
tions in  its  supply  from  without. 

Accumulation  of  Glucose  in  the  Blood,  and  its  Discharge  by  the 
Urine. — Under  ordinary  conditions  the  glucose  thus  formed  does  not 
pass  beyond  the  general  circulation.  But  if  from  any  cause  its  quantity 
in  the  blood  be  raised  above  a  certain  proportion,  it  fails  to  be  com- 
pletely assimilated,  and  a  part  is  discharged  by  the  kidneys,  producing 

*  Comptes  Kendus  de  1' Academic  des  Sciences.  Paris,  1876,  tome  Ixxxii.,  pp.  369, 
407. 

O 


210  FUNCTIONS    OF    NUTRITION. 

a  condition  of  diabetes.  Yon  Becker*  found  that  in  rabbits,  if  glucose 
be  present  in  the  blood  in  the  proportion  of  5  parts  per  thousand,  it 
passes  off  by  the  urine,  where  it  may  be  recognized  by  the  copper  test ; 
but  if  less  abundant  than  this,  its  indications  in  the  urine  are  faint  and 
uncertain.  Bernard, f  by  injecting  a  solution  of  glucose  into  the  veins 
of  the  rabbit,  generally  produced  a  condition  of  diabetes  when  the  glu- 
cose was  injected  in  larger  quantity  than  one  part  per  thousand  of  the 
bodily  weight.  The  effect  of  such  injections  is,  however,  temporary, 
passing  off  when  the  surplus  of  saccharine  matter  has  been  expelled 
from  the  system.  According  to  Yon  Becker,  a  solution  of  glucose, 
injected  into  the  jugular  vein  of  the  rabbit  in  sufficient  quantity,  may 
cause  the  appearance  of  sugar  in  the  urine  in  less  than  three  hours; 
but  at  the  end  of  six  or  seven  hours  the  whole  of  it  may  be  eliminated, 
so  that  it  is  no  longer  found  in  the  excretions. 

A  variety  of  circumstances  may  so  increase  the  proportion  of  glucose 
in  the  blood  as  to  cause  a  saccharine  condition  of  the  urine. 

I.  One  of  these  causes  is  an  unusually  abundant  and  rapid  absorp- 
tion of  sugar  from  the  intestine.     Where  a  very  large  quantity  of 
sugar  is  suddenly  absorbed,  and  at  once  carried  by  the  portal  vein  to 
the  liver,  this  organ  is  not  capable  of  immediately  converting  the  whole 
of  it  into  glycogen.     A  portion  thus  passes  the  hepatic  circulation  un- 
changed, and,  reaching  the  general  circulation  in  unusual  quantity,  is 
discharged  with  the  urine.     Yon  Becker  observed  that  when  concen- 
trated solutions  of  glucose  are  introduced  in  abundance  into  the  intes- 
tine of  the  rabbit,  it  may  subsequently  appear  in  the  urine.     Bernard 
also  found  that  if  in  the  rabbit,  after  one  or  two  days'  fasting,  sugar  in 
large  amount  be  injected  into  the  stomach,  the  urine  becomes  diabetic ; 
and  he  observed  the  same  thing  in  the  human  subject,  in  consequence 
of  taking  a  large  quantity  of  sugar  in  solution  when  the  stomach  had 
been  empty  for  several  hours.     This  result  is  produced  only  when  a 
much  greater  abundance  of  sugar  is  present  in  the  intestine  than  in 
ordinary  digestion,  and  depends  on  the  excessive  quantity  absorbed  in 
a  short  time. 

II.  A  diabetic  condition   may  also  be  induced  by  anything  which 
hastens  the  circulation  through  the  liver,  or  increases  its  supply  of 
blood.     Many  observers  have  met  with  this  result  from  a  variety  of 
causes.      Bernard  found  that  in  dogs  the  venous  blood  may  present 
traces  of  glucose  after  the  abdomen  has  been  subjected  to  pressure  or 
manipulation  over  the  region  of  the  liver,  and  after  continued  struggles 
or  convulsive  action,  by  which  the  abdominal  organs  are  forcibly  com- 
pressed.     In  the  same  animal,  according  to  Harley,  the  injection  of 
weak  solutions  of  ammonia  or  ether  into  the  portal  vein  may  be  followed 
by  a  saccharine  condition  of  the  urine.     It  has  also  been  observc'd  in 
man,  after  a  bruise  in  the  right  hypochondriac  region.     The  resistance 


*  Zeitsohrift  fiir  wissenschaftliche  ZoologU',  Hand  v.,  p.  176. 

f  Le9ons  sur  lea  Liquides  de  I'Organisme.     Paris,  1859,  tome  ii.,  p.  73. 


ABSORPTION.  211 

of  an  animal  to  the  inhalation  of  ether  and  his  subsequent  muscular 
relaxation,  general  paralysis  from  fracture  of  the  skull  with  cerebral 
hemorrhage,  and  the  action  of  curare,  which  also  causes  complete  mus- 
cular paralysis,  are  all  known  to  be  sometimes  followed  by  sugar  in  the 
urine.  Schiff*  has  even  found  that,  in  various  animals,  compression 
of  the  abdominal  aorta  for  ten  minutes,  or  tying  the  principal  blood- 
vessels of  one  limb,  may  induce,  for  the  time  being,  a  condition  of  dia- 
betes. All  these  causes  probably  operate  by  accelerating  the  hepatic 
circulation. 

III.  Saccharine  urine  may  also  be  produced  by  puncture  of  the 
medulla  oblongata  in  the  floor  of  the  fourth  ventricle.  This  fact,  first 
discovered  by  Bernard, f  is  best  shown  in  the  rabbit  by  introducing 
a  narrow  chisel-shaped  instrument,  with  the  cutting  edge  directly 
transversely,  through  the  back  part  of  the  skull  and  the  cerebellum, 
so  that  it  shall  pierce  the  posterior  part  of  the  medulla  in  the  median 
line,  without  passing  completely  through  its  substance.  Glucose  ap- 
pears in  the  urine  after  one  or  two  hours  and  continues  to  be  present 
for  several  days.  The  immediate  effect  of  this  operation,  according 
to  Bernard,  is  to  increase  the  activity  of  the  abdominal  circulation. 
When  successfully  performed,  the  operation  causes  no  serious  disturb- 
ance of  the  vital  functions,  and  the  animal  recovers  without  permanent 
injury. 

In  all  the  above  instances,  the  appearance  of  sugar  in  the  urine  is 
temporary,  depending  on  occasional  disturbance  of  the  circulation. 
When,  in  man,  this  condition  becomes  permanent,  it  constitutes  the 
disease  known  as  Diabetes  mellitus.  In  this  affection,  which  is  gen- 
erally progressive  and  fatal,  the  urine  is  increased  in  quan  tity ,  of  high 
specific  gravity,  and  continuously  charged  with  glucose,  sometimes  in 
great  abundance.  Fluctuations  are  observable  in  its  quantity  at  differ- 
ent periods  of  digestion  and  under  the  use  of  different  articles  of  food ; 
saccharine  and  starchy  substances  causing  its  increase,  and  albuminous 
matters  its  diminution.  But  it  usually  continues  to  appear  in  some 
proportion,  whatever  regimen  be  adopted. 

*  Journal  de  PAnatomie  et  de  la  Physiologic.     Paris,  1866,  No.  iv.,  p.  365. 
f.  Lepons  de  Physiologic  Experimentale.    Paris,  1855,  p.  290. 


CHAPTER    III. 
THE    BLOOD. 

THE  blood  is  a  thick,  opaque  fluid,  varying  in  different  parts  of  the 
body  from  a  brilliant  scarlet  to  a  dark  purple  or  nearly  black  color. 
It  has  a  slightly  alkaline  reaction,  and  a  specific  gravity  of  1,055.  It 
consists,  first,  of  a  nearly  colorless,  transparent,  alkaline  fluid,  the  plas- 
ma, containing  water,  albuminous  matters,  and  salts,  in  solution  ;  and, 
secondly,  of  distinct  corpuscles,  or  blood  globules,  swimming  in  the 
liquid  plasma.  The  globules  form  about  40  per  cent.,  the  plasma 
about  60  per  cent,  by  volume,  of  the  entire  mass.  The  specific  gravity 
of  the  two  is  somewhat  different.  That  of  the  plasma  is  about  1030; 
that  of  the  globules,  1088.  Their  relative  quantities,  by  weight,  are 
therefore  more  nearly  equal  than  when  estimated  by  volume  ;  the  exact 
proportions,  according  to  Robin,  being  nearly  45  per  cent,  of  globules 
and  55  per  cent,  of  plasma. 

Notwithstanding  the  difference  in  specific  gravity  between  the  blood- 
globules  and  plasma,  the  natural  movement  of  the  blood  in  the  circu- 
lation keeps  them  thoroughly  mingled ;  and  even  when  it  is  allowed  to 
remain  at  rest,  the  globules  subside  very  slowly  and  imperfectly.  Thus 
the  globules,  uniformly  disseminated  through  the  plasma,  give  to  the 
blood  an  opaque  aspect  and  deep  red  color. 

The  globules  of  the  blood  are  of  two  kinds,  red  and  white ;  of  which 
the  red  are  far  the  most  numerous. 

Red  Globules  of  the  Blood. 

The  red  globules  of  human  blood  are  so  abundant  that,  in  the  thinnest 
layer  under  the  microscope,  they  cover  or  touch  each  other  in  every 
direction.  According  to  the  estimates  of  Welcker  and  Vierordt  about 
5  millions  are  contained  in  each  cubic  millimetre  of  blood.  On  account 
of  their  quantity  therefore,  as  well  as  their  properties,  they  form  a  most 
important  constituent  of  the  circulating  fluid. 

Physical  Properties  of  the  Red  Globules. — The  red  globules  of  hu- 
man blood  present,  under  the  microscope,  a  circular  figure  and  a  smooth 
exterior.  According  to  the  most  recent  measurements,  they  have,  on 
the  average,  a  transverse  diameter  of  from  7.50  to  7.75  mmm.  Their 
size  varies  more  or  less,  but  this  variation  is  not  very  marked  for  the 
greater  number,  and,  according  to  Schmidt,  over  90  per  cent,  of  those 
contained  in  a  single  specimen  have  the  same  dimensions.  The  smallest 
size  observed  is  4.50  mmm.  (Harting),  and  the  largest  9.3  mmm.  ;  while 

212 


THE    BLOOD. 


213 


of  the  red   blood-globule   is   that   of  a   spheroid,  much 
its   opposite   sur- 

FIG.  43. 


HUMAN  BLOOD-GLOBULES.— a.  Ked  globules,  seen 
flatwise.  6.  Red  globules,  seen  edgewise,  c.  White 
globule. 


their  average  diameter,  in  different  individuals,  varies  from  6  70  to 
8.20  mmm. 

The  form 
flattened    on 

faces,  somewhat  like  a  thick 
piece  of  money  with  rounded 
edges.  If  seen  flatwise  it  shows 
a  broad  surface  and  a  circular 
outline  (Fig.  43,  a);  but  if 
made  to  roll  over,  it  presents, 
during  its  rotation,  the  flattened 
form  indicated  at  b.  Its  thick- 
ness is  about  one-fifth  of  its 
transverse  diameter.  When 
lying  on  their  broad  surfaces, 
it  can  be  seen  that  the  globules 
are  not  exactly  flat,  but  that 
there  is  on  each  side  a  central 
depression,  the  rounded  edges 
being  thicker  than  the  middle 
portion.  This  produces  a  differ- 
ent appearance  of  the  globules 
when  examined  within  and  without  the  exact  focus  of  the  microscope. 
The  substance  of  which  they  are  composed  is  more  refractive  than  the 
plasma  in  which  they  are  immersed.  When  viewed,  therefore,  by  trans- 
mitted light,  their  thick  edges  act  as  double  convex  lenses,  and  con- 
centrate the  light  above  the  level  of  the  fluid.  Consequently,  if  the 
object-glass  of  the  microscope  be  slightly  raised,  so  that  the  globules 
fall  beyond  its  focus,  their  edges  will  appear  brighter.  But  their  cen- 
tral portions  act  as  double  concave  lenses,  and  disperse  the  light  from 
a  point  below  the  level  of  the  fluid.  They  thus  become  brighter  when 
the  object-glass  is  carried  downward  and  the  globules  fall  within  its 
focus.  An  alternating  appearance  of  the  globules  may,  therefore,  be 
produced  by  viewing  them  first  beyond  and  then  within  the  focus  of  the 
instrument.  When  beyond  the  focus,  they  are  seen  with  a  bright  rim 
and  a  dark  centre.  Within  it,  they  have  a  dark  rim  and  a  bright  centre. 

When  placed  under  the  microscope,  the  blood-globules,  after  a  fluc- 
tuating movement  of  short  duration,  often  arrange  themselves  in 
slightly  curved  rows,  adhering  to  each  other  by  their  flat  surfaces, 
and  presenting  an  appearance  like  that  of  rolls  of  coin.  This  is  prob- 
ably due  to  the  coagulation  of  the  blood,  which  takes  place  very  rapidly 
when  in  thin  layers  and  in  contact  with  glass  surfaces ;  thus  forcing 
the  globules  into  a  position  to  occupy  the  least  space. 

The  color  of  the  blood-globules,  viewed  by  transmitted  light  and  in 
thin  layers,  is  a  light  amber  or  pale  yellow.  By  reflected  light,  or 
in  thick  layers,  it  is  deep  red.  Their  consistency  is  nearly  fluid.  They 
are  very  flexible,  and  easily  elongated,  bent,  or  distorted  in  passing 


211 


FUNCTIONS    OF    NUTRITION. 


FIG.  44. 


RED  GLOBULES  OF  THE  BLOOD,  adhering  to- 
gether, like  rolls  of  coin. 


through  the  narrow  channels  and  currents,  often  seen  in  a  drop  of 
blood  under  microscopic  examination ;  but  they  regain  their  original 
shape  as  soon  as  the  pressure  is  taken  off. 

So  far  as  observation  can  determine,  the  red  globules  of  the  blood, 

in  man  and  mammalians,  are 
homogeneous  in  structure; 
showing  no  distinction  between 
an  external  envelope  and  the 
parts  within.  Although  some 
microscopists  of  high  repute 
(Kolliker,  Richardson)  continue 
to  regard  the  existence  of  an 
exterior  membrane  as  probable, 
it  is  not  generally  admitted,  and 
cannot  be  directly  demonstrated. 
Each  globule  appears  like  a  mass 
of  organic  substance  of  the  same 
color,  consistency,  and  composi- 
tion throughout. 

The  blood-globules  are  altered 
by  various  physical  and  chemi- 
cal agents.  If  a  drop  of  blood 
under  the  microscope  be  not  protected  from  evaporation,  the  globules 
near  the  edges  of  the  preparation  often  dimmish  in  size,  becoming 
shrivelled  and  notched  at  their  margins ;  an  effect  apparently  due  to 
the  partial  loss  of  their  watery  ingredients.  This  alteration  some- 
times takes  place  with  great  rapidity  in  blood  withdrawn  for  exami- 
nation; but,  according  to  Kol- 
liker, it  is  never  seen  in  the 
blood  while  circulating  in  the 
vessels. 

If  water,  on  the  other  hand, 
be  added  to  the  blood,  the  red 
globules  absorb  it  by  imbibition, 
lose  their  central  concavity,  as- 
sume the  spherical  form,  and 
become  paler.  A  large  quan- 
tity of  water  may  completely 
extract  the  coloring  matter, 
leaving  the  globules  as  pale, 
colorless  circles,  almost  invis- 
ible from  their  tenuity.  In 
this  condition  they  may  again 

be    brought    into    view   by    add-        RKDGLOBI  -u.s  m ,-,  UK  BLOOD,  shrunken,  with 
J  their  margins  notched. 

ing   an    iodine    solution,  which 

stains  them  of  a  yellowish  color.     If  water   be   added    in  quantity 

just    sufficient   to   be   imbibed    by   the   globules,   without   extracting 


FIG.  45. 


THE    BLOOD. 


215 


FIG.  46. 


their  coloring  matter,  a  special  change  in  their  form  is  exhibited. 
Their  thick  edges,  absorbing  water  more  abundantly  than  the  rest, 
become  turgid,  and  encroach  gradually  on  the  central  part.  The 
central  depression,  under  these  circumstances,  may  disappear  on  one 
side  before  it  is  lost  on  the  other,  so  that  the  globule,  as  it  swells 
up,  curls  over  laterally,  and  assumes  a  cup-shaped  form.  (Fig.  46, 
a,  a.)  This  may  often  be  seen  in  blood-globules  after  soaking  for 
some  time  in  the  urine,  or  other  animal  fluids  of  less  density  than 
the  plasma  of  the  blood.  Dilute  acetic  acid  at  once  extracts  the  color- 
ing matter  of  the  globules,  reducing  them  to  the  condition  of  pale  and 
nearly  invisible  colorless  bodies,  which,  however,  remain  for  a  long 
time,  and  are  dissolved  very 
slowly  in  comparison  with  the 
coloring  matter. 

Dilute  alkaline  solutions,  on 
the  contrary,  readily  dissolve 
the  whole  substance  of  the 
blood-globules.  A  solution  of 
potassium  hydrate,  in  the  pro- 
portion of  ten  per  cent.,  acts 
most  rapidly  in  this  manner. 
Solutions  of  soda  and  ammonia 
have  a  similar  effect,  though 
less  promptly  than  the  preced- 
ing- 
Solutions  of  sodium  glyco- 
cholate  or  taurocholate,  in  any 
grade  of  concentration,  or  of  the 
fresh  bile  itself,  as  shown  by 
Kiihne,  also  dissolve  the  red  globules  of  the  blood. 

Composition  of  the  Red  Globules. — The  red  globules  are  composed 
of  an  albuminous  and  a  coloring  matter,  with  mineral  salts  and  water. 
According  to  Lehmann,  the  water  of  the  red  globules  amounts  to  688 
per  thousand  parts ;  a  little  over  8  parts  per  thousand  consisting  of 
mineral  salts,  namely,  sodium  and  potassium  chlorides,  phosphates,  and 
sulphates,  together  with  lime  and  magnesium  phosphates. 

The  most  important  ingredient  of  the  red  globules  is  their  coloring 
matter,  or  hemocjlobine.  According  to  the  estimates  of  Preyer,*  founded 
on  the  observed  quantity  of  iron  as  an  ingredient,  the  average  pro- 
portion of  hemoglobine  in  human  blood  is  12.34  per  cent.  As  the 
globules  constitute  45  per  cent,  of  the  entire  blood,  the  quantity  of 
hemoglobine  in  each  globule  is  about  21  per  cent,  of  its  mass,  or  86  per 
cent,  of  its  solid  ingredients.  It  is  accordingly  the  principal  substance 
of  which  the  globules  are  composed. 

In  the  fresh  globule  the  hemoglobine  is  united  with  a  colorless  albu- 


EED  GLOBULES  OF  BLOOD,  after  the  imbibition 
of  water. 


*Die  Blutkrystalle.     Jena,  1871,  p.  117. 


216  FUNCTIONS    OF    NUTRITION, 

minous  matter,  which  forms  a  substratum  for  its  other  ingredients. 
This  substance  is  less  soluble  in  water  than  hemoglobine,  and  remains 
behind  when  the  latter  has  been  dissolved  out,  leaving  the  globules  de- 
colorized and  reduced  in  volume.  The  exact  condition  of  hemoglobine 
in  the  blood-globule,  and  its  mode  of  union  with  the  colorless  sub- 
stratum, are  not  positively  known.  Preyer  calculates  that  the  water 
of  the  globule  is  insufficient  to  hold  in  solution  the  quantity  of  hemoglo- 
bine present ;  and  on  the  other  hand,  as  the  crystals  of  hemoglobine  are 
doubly  refracting,  while  the  fresh  globules  are  not  so,  the  hemoglobine 
cannot  exist  in  the  globules  in  a  solid  form.  So  far  as  we  can  judge,  the 
two  substances  are  uniformly  united  in  a  condition  of  semi-fluidity ; 
but  the  hemoglobine,  being  more  easily  affected  by  various  dissolving 
agents,  may  be  extracted  by  this  means  from  the  mass  of  the  globule. 

The  avidity  of  hemoglobine  for  free  oxygen,  and  its  readiness  to  part 
with  this  substance  under  favorable  conditions,  cause  it  to  assume  alter- 
nately the  two  different  forms  of  "  oxyhemoglobine "  and  "reduced 
hemoglobine  "  (page  94).  The  former  gives  its  bright  scarlet  hue  to  arte- 
rial blood,  the  latter  is  the  dark  purple  coloring  matter  of  venous  blood. 

Red  Globules  of  the  Blood  in  Different  Classes  of  Animals. — In  all 
vertebrate  animals  the  red  globules  contain  a  coloring  matter  identical, 
in  its  optical  and  physiological  properties,  with  that  of  human  blood ; 
but  they  present  varieties  of  form,  size,  and  structure  more  or  less  char- 
acteristic of  different  classes,  families,  and  species. 

In  the  mammalians,  or  warm-blooded  quadrupeds,  the  red  globules 
have  without  exception  the  same  homogeneous  structure  as  in  man. 
They  have  also  the  same  circular  disk-like  figure,  except  in  the  family 
of  camelidae  (camel,  dromedary,  lama),  where  the  disks  are  oval.  Their 
size  varies  much  in  extreme  cases,  the  smallest  known  being  those  of 
the  Java  musk-deer,  an  animal  not  larger  than  a  rabbit,  which  have  a 
diameter  of  2.50  mmm.,  while  the  largest  are  those  of  the  elephant, 
which  measure  9.20  mmm.  Their  size,  however,  does  not  always  cor- 
respond with  that  of  the  animal,  since  those  of  the  cat  are  larger  than 
those  of  the  sheep,  and  those  of  the  rabbit  larger  than  either.  The  fol- 
lowing list  gives  the  size  of  the  red  globules  in  various  species  accord- 
ing to  the  measurements  of  Gulliver  and  Welcker : 

DIAMETER  OF  THE  RED  BLOOD-GLOBULES  OF  MAMMALIANS, 
in  Micro-Millimetres. 

Elephant  ....  9.20  Fox  .  .  .  6.10 

Sloth  ....  8.93  Ox    .  ...  5.95 

Ape  ....  7.35  Horse  .  .  .  5.43 

Dog  ....  7.30  Sheep  .  .  .  5.00 

Wolf  ....  6.94  Red  deer  .  .  .  5.00 

Rabbit  ....  6.90  Goat  .  .  .  4.10 

Cat  ....  6.50  Musk  <Wr  .  .  2.50 

In  animals  where  the  red  globules  are  small,  they  are  proportionately 
numerous.  It  is  estimated  by  Kolliker  that  the  mass  of  all  the  red 


THE    BLOOD. 


217 


FIG.  47. 


globules  together,  in  any  given  quantity  of  blood,  does  not  vary  much 
in  different  species ;  but  in  blood  containing  the  smaller  and  more 
abundant  globules,  their  extent  of  surface,  and  probably  their  func- 
tional activity,  is  greater  than  where  they  are  larger  and  less  numerous. 
This  will  also  apply  to  the  inferior  vertebrate  animals,  in  which  the 
globules  are  often  much  larger  and  less  numerous  than  in  man. 

In  birds,  reptiles,  and  fish,  comprising  all  the  oviparous  vertebrata  as 
well  as  some  which  are  viviparous,  the  red  globules  are  distinguished 
by  two  marked  characters  of  shape  and  structure,  namely,  an  oval 
form  and  the  presence  of  a  nucleus.  The  only  known  exceptions 
are  two  species  of  fish,  belonging  to  the  family  of  the  Lampreys,  in 
which  the  globules  have  a  circular  outline ;  but  here  also  they  are 
provided  with  a  nucleus,  and  are  therefore  distinguishable  from  the 
circular  globules  of  mammalia. 

In  the  Batrachians,  or  naked 
reptiles,  the  red  globules  pre- 
sent the  largest  size  and  exhibit 
most  distinctly  their  structural 
character.  They  are  of  a  regu- 
larly oval  form,  somewhat 
thicker  toward  the  edges  and 
thinner  in  the  middle,  the  round 
or  oval,  colorless,  and  granular 
nucleus  projecting  slightly  from 
the  lateral  surface  at  its  central 
portion.  In  their  reaction  un- 
der different  physical  and  chem- 
ical conditions,  they  resemble 
the  red  globules  of  mammalians. 

In  the  frog  the  red  globules 
have  a  long  diameter  of  22  mmm. , 
or  nearly  three  times  that  of  the  human  globules;  in  Proteus  anguinus, 
the  blind  water-lizard  of  the  Carniola  grottoes,  58  mmm. ;  in  Meno- 
branchus,  a  species  inhabiting  the  northern  lakes  of  the  United  States, 
62.5  mmm. ;  and  in  Amphiuma  tridactylum,  the  great  water-lizard  of 
Louisiana,  according  to  Riddell,  they  are  one-third  larger  than  in 
Proteus,  or  about  77  mmm.  The  following  list  gives  the  size  of  dif- 
ferent globules  of  the  oval  form. 

LONG  DIAMETER  OF  THE  OVAL  RED  GLOBULES  OF  BIRDS,  REPTILES,  AND  FISH, 

in  Micro-Millimetres. 

Fowl 
Duck 
Pigeon     . 
Lizard 

Alligator 
Tortoise  . 
Frog 


BLOOD-GLOBULES  OP  FROG.— a.  Red  globule  seen 
edgewise,    b.  White  globule. 


12.1 

Triton      . 

.       29.3 

12.9 

Proteus    . 

.      58.0 

14.7 

Menobranchus 

.       62.5 

16.4 

Ampliiuma 

.      77.0 

19.2 

Perch       . 

.       12.0 

20.0 

Carp 

.       13.1 

22.0 

Sturgeon  . 

.       13.4 

218  FUNCTIONS    OF    NUTRITION. 

Diagnosis  of  Blood,  and  the  distinction  between  Human  Blood  and 
that  of  Animals. — It  is  often  of  consequence  to  recognize  blood  in 
various  animal  fluids  in  physiological  experiments,  and  it  sometimes 
becomes  important  in  medico-legal  investigations.  For  this  purpose,  in 
the  fresh  fluids,  nothing  can  be  more  satisfactory  than  spectroscopic  ex- 
amination ;  a  very  small  quantity  of  hemoglobine  being  sufficient  to 
yield  a  spectrum  with  the  characteristic  absorption  bands.  This  method 
has  the  further  advantage  that  it  enables  us  to  detect  the  presence  of 
blood  where  its  globules  have  been  dissolved  or  their  coloring  matter 
reduced  to  a  fluid  condition.  The  washings  of  a  blood  stain  may  show 
the  spectrum  of  hemoglobine,  although  they  may  not  contain  any  red 
globules  perceptible  by  the  microscope.  This,  however,  only  show*  the 
presence  of  the  coloring  matter  of  blood,  and  allows  us  to  distinguish  it 
from  other  colored  fluids ;  it  does  not  distinguish  between  the  blood  of 
man  and  that  of  animals,  since  the  hemoglobine  is  the  same  in  all. 

But  by  microscopic  examination  of  the  red  globules,  either  when 
fresh  or  after  having  been  dried  and  again  moistened,  we  can  often  dis- 
tinguish the  blood  of  an  inferior  animal  from  that  of  man.  According 
to  Richardson,*  a  fragment  of  dried  blood,  weighing  less  than  y^  of 
a  milligramme,  which  has  been  kept  for  five  years,  if  decolorized  with  a 
weak  watery  solution  (O.T5  per  cent.)  of  sodium  chloride,  and  afterward 
tinted  with  aniline,  may  exhibit  the  blood-globules  in  such  a  condition 
that  their  size  can  be  accurately  measured. 

If  a  blood  stain,  accordingly,  which  in  watery  solution  gives  the 
spectrum  of  hemoglobine,  be  found  to  contain  oval  nucleated  globules, 
it  must  be  the  blood  of  a  bird,  reptile,  or  fish ;  and  the  oval  form  alone 
would  show  that  it  is  not  human  blood.  The  question  whether  a  speci- 
men be  composed  of  human  blood  may  consequently  be  decided  in  the, 
negative  by  microscopic  examination.  But  if  the  specimen  contain  cir- 
cular globules,  without  nuclei,  it  will  be  impossible  to  say  whether  they 
belong  to  human  blood,  or  to  that  of  some  animal,  such  as  the  ape  or 
the  dog,  whose  globules  nearly  approach  the  human  in  size.  In  most 
domesticated  quadrupeds,  the  globules  are  smaller  than  in  human  blood ; 
while  in  both  the  sloth  and  the  elephant,  they  are  larger.  If  it  wrre 
only  required  to  decide  whether  a  specimen  of  blood  belonged  to  man, 
or  to  the  elephant  or  the  musk  deer,  for  example,  or  even  to  the  goat, 
no  doubt  the  difference  in  size  of  the  globules  would  be  sufficient  to 
determine  the  question. 

But  within  nearer  limits  of  resemblance  it  would  be  doubtful,  because 
the  size  of  the  globules  varies  to  some  extent  in  each  kind  of  blood  ; 
and  in  order  to  be  certain  that  a  particular  s]>ecinieu  were  human  blood, 
it  would  be  necessary  to  show  that  the  smallest  of  its  globules  wore 
larger  than  the  largest  of  those  belonging  to  the  animal  in  question,  or 
vice  versa.  The  limits  of  this  variation  have  been  tolerably  well  de- 
fined for  human  blood,  but  not  sufficiently  so  for  many  of  the  lower 
animals  to  make  an  absolute  distinction  possible. 

*  Monthly  Microscopical  Journal.     London,  Sepk'iulHT  1,  1S71,  \>.  140. 


THE    BLOOD.  219 

In  the  examination  of  stains  or  blood  spots,  the  difficulty  is  increased 
by  the  fact  that  the  drying  and  subsequent  moistening  of  the  globules 
introduces  another  element  of  uncertainty  as  to  their  original  size. 

Physiological  Function  of  the  Red  Globules. — The  red  globules  of 
the  blood  serve  mainly  as  carriers  of  oxygen.  The  readiness  with 
which  they  absorb  this  substance  from  the  atmosphere,  and  their  changes 
of  color  depending  upon  its  supply  or  withdrawal,  indicate  that  they 
have  a  special  relation  to  its  introduction  and  distribution  in  the  body. 
As  a  rule,  in  animals  where  the  red  globules  are  of  large  size  and  few 
in  number,  the  activity  of  the  vital  functions  is  below  the  average ;  while 
in  the  species  where  they  are  smaller  and  more  numerous,  the  processes 
of  respiration,  circulation,  nutrition,  and  movement  are  increased  in 
rapidity  to  a  similar  degree.  The  strongly  marked  physical  and  chemi- 
cal characters  of  the  red  globules  correspond  with  their  importance  in 
the  functions  of  vitality. 

White  Globules  of  the  Blood. 

Beside  the  red  globules  the  blood  contains  other  cellular  bodies,  differ- 
ing from  the  former  in  several  important  particulars.  These  are  the 
white  globules.  As  their  name  implies,  they  are  destitute  of  coloring 
matter,  but  they  present,  under  the  microscope,  a  glistening  appearance, 
and  when  collected  in  large  quantity  may  give  to  the  fluid  or  clot  which 
contains  them  a  whitish  hue.  They  are  much  less  abundant  than  the 
red  globules,  the  average  proportion  in  human  blood  being  one  white 
globule  to  300  red.  They  are  nearly  spherical  in  form,  and,  on  the 
average,  11  mmm.  in  diameter.  They  are,  accordingly,  in  human  blood, 
distinctly  larger  than  the  red  globules/  (Fig.  43,  c.)  They  consist  of 
a  soft,  somewhat  viscid,  finely  granular  substance,  containing  one,  two, 
or  three  ovoid  nuclei.  They  are  less  yielding  and  slippery  than  the  red 
globules,  and  adhere  more  readily  to  surfaces  with  which  they  are  in 
contact.  When  a  little  watery  fluid  is  added  to  a  drop  of  blood  under 
examination,  the  red  globules  will  be  hurried  away  by  the  currents  pro- 
duced, while  the  white  globules  lag  behind,  and,  if  the  irrigation  be  con- 
tinued, may  finally  be  left  alone  in  the  field  of  the  microscope.  Their 
transparency  is  such  that,  when  slowly  rolling  over  with  the  current, 
the  granules  in  their  interior  may  often  be  seen  to  rotate  past  each  other, 
with  the  motion  of  the  globule.  The  nuclei  are  sometimes  visible  in  the 
fresh  globule,  but  may  always  be  brought  into  view  by  the  addition  of 
water  or  of  dilute  acetic  acid.  These  fluids  cause  a  slight  swelling  of  the 
globule  and  an  increase  of  its  transparency,  by  which  the  nuclei  become 
perceptible  as  sharply  defined  ovoid  or  vesicular  bodies,  near  the  central 
part  of  the  mass.  By  the  prolonged  action  of  acetic  acid,  a  portion  of 
the  cell  substance  becomes  condensed  about  the  nuclei  in  various  irregu- 
lar forms,  while  the  remainder  appears  transparent  and  homogeneous, 
with  a  delicate  circular  outline.  The  final  effect  of  both  water  and  acetic 
acid  is  to  disintegrate  the  white  globules  and  cause  their  disappearance. 
Dilute  alkalies  dissolve  them  with  great  readiness. 


220 


FUNCTIONS    OF    NUTRITION. 


FIG.  48. 


Amoeboid  Movement  of  the  White  Globules. — This  movement  is  so 
called  from  its  resemblance  to  those  of  Amoeba,  a  minute  animal  form, 

of  simple  organization,  living  in 
fresh -water  pools  and  ditches. 
It  is  never  perceptible  while  the 
blood  is  circulating  normally 
in  the  blood-vessels,  where  the 
white  globules  always  present 
a  rounded  and  uniformly  granu- 
lar appearance  But  soon  after 
the  blood  has  been  withdrawn, 
if  maintained  at  or  near  its  nor- 
mal temperature,  the  white  glob- 
ules may  be  seen  to  alter  their 
shape  in  a  remarkable  way  A 
portion  of  the  rounded  outline 
of  the  globule  first  becomes  faint 
and  irregular,  flattening  out  and 
extending  itself  into  one  or  more 
transparent,  homogeneous-look- 
ing prolongations.  These  prolongations  are  alternately  protruded  and 
retracted,  sometimes  extending  into  long  filamentous  processes,  some- 
times into  shorter  expansions  with  rounded  ends.  The  variations  in 
form  thus  produced  succeed  each  other  with  different  degrees  of  rapidity, 
according  to  circumstances.  In  man  and  the  warm-blooded  animals, 
the  blood  requires  to  be  kept  at  about  the  temperature  of  the  living 
body,  in  order  that  these  appearances  may  be  exhibited;  but  in  the 
cold-blooded  animals  they  may  be  shown  at  the  ordinary  temperature 
of  the  air. 

Beside  these  changes  of  form,  the  white  globules  of  the  blood  may 
sometimes  be  seen,  by  a  similar  mechanism,  to  move  from  place  to 
place.  In  these  cases,  the  globule  first  sends  out  the  pale  prolonga- 
tions above  described.  The  granules  of  the  remaining  portion  are  then 

FIG.  49. 


WHITE  GLOBULES  OF  HUMAN  BLOOD  ;  altered  by 
dilute  acetic  acid. 


CHANGES  IN  FORM  OF  A  WHITE  BLOOD-GLOBULE  of  the  Newt  (Triton  MiBqpWMtafur),  occurring  in 
an  interval  of  seven  minutes,  and  within  half  an  hour  after  its  extraction  from  the  living  body. 

propelled,  by  a  kind  of  flowing  movement,  into  the  prolongations, 
which  thus  become  granular,  and  at  the  same  time  assume  a  more 
rounded  form.  The  remaining  portion  is  subsequently  drawn  after 


THE    BLOOD.  221 

and  into  the  part  previously  expanded ;  and  by  a  continuance  of  this 
process  the  whole  mass  makes  a  slow  progression  across  the  field  of 
the  microscope. 

These  movements  are  accomplished,  like  those  of  the  amoeba,  by  local 
contractions  and  relaxations  of  the  substance  of  the  globule.  In  Amoeba 
princeps  the  movement  of  progression  may  take  place  at  the  rate  of  73 
micro-millimetres  per  minute,  and  in  some  gelatinous  animalcules  it  is 
so  active  that  it  may  be  followed  continuously  by  the  eye.  But  the 
movement  of  the  white  globules  of  the  blood  is  much  more  slowly 
performed,  and,  like  that  of  the  hour-hand  of  a  clock,  is  to  be  distin- 
guished only  by  noting  their  change  of  position  after  a  certain  time. 
The  white  globules  of  the  frog,  on  the  free  surface  of  the  mesentery, 
may  move  at  a  rate,  as  measured  by  the  micrometer,  of  13  micro- 
millimetres  per  minute ;  and  similar  granular  corpuscles,  in  the  con- 
nective tissue  of  the  mesentery,  may  progress  at  the  rate  of  3.5  micro- 
millimetres  in  the  same  time.  Certain  cells  in  the  frog's  cornea,  regarded 
by  some  observers  as  identical  with  the  white  globules  of  the  blood, 
may  change  their  position  in  the  cornea  at  the  rate  of  2.5  micro-milli- 
metres per  minute. 

The  amoeboid  movement  is  sometimes  seen  in  the  interior  of  the 
capillary  blood-vessels  or  small  veins,  when  the  globules  are  imprisoned 
in  a  stagnant  portion  of  the  blood-plasma.  But  if  the  circulation  be 
reestablished,  as  the  globules  again  move  with  the  blood  current,  they 
cease  to  be  distorted,  and  resume  their  rounded  form. 

The  physiological  properties  and  functions  of  the  white  corpuscles 
are  not  so  distinct  as  those  of  the  red  globules.  Their  great  inferiority 
in  number  shows  that  they  are  less  important  for  the  immediate  con- 
tinuance of  the  vital  operations ;  and  the  same  thing  may  be  inferred 
from  their  want  of  strongly  marked  specific  characters.  For  while  the 
red  globules  of  the  blood  vary  in  appearance  to  a  marked  degree  in  dif- 
ferent classes,  orders,  and  families,  the  white  globules  present  nearly 
the  same  general  features  of  size,  form,  and  structure  throughout  the 
series  of  vertebrate  animals. 

Plasma  of  the  Blood. 

The  plasma  is  a  transparent,  colorless,  homogeneous  liquid,  in  which 
the  blood-globules  are  suspended.  It  consists  of  water,  holding  in  solu- 
tion mineral  salts  and  albuminous  matters,  with  various  crystallizable 
substances  of  organic  origin.  Its  albuminous  matters  are  the  most 
abundant  and  important  of  its  solid  ingredients.  Its  average  compo- 
sition, according  to  the  most  careful  estimates,  is  as  follows : 

COMPOSITION  OF  THE  BLOOD-PLASMA. 

Water 902.00 

Albumen 53.00 

Paraglobuline 22.00 

Fibrinogen     ......... 

Fatty  matters 2-50 


222  FUNCTIONS    OF    NUTRITION. 

Crystallizahle  nitrogenous  matters   ....  4.00 

Other  organic  ingredients 5.00 

Sodium  chloride  "] 

Potassium  chloride 

Sodium  carl.onate  Mineral  salts  8.50 

Sodium  and  potassium  sulphates 

Sodium  and  potassium  phosphates 

Lime  and  magnesium  phosphates       J 

1000.00 

Of  these  substances,  albumen  no  doubt  holds  the  first  place  in  regard 
to  nutrition,  as  it  presents,  in  a  high  degree,  the  character  of  a  nutritious 
material.  It,  in  all  probability,  supplies  the  greater  part  of  the  nitro- 
genous ingredients  of  the  tissues,  and  provides  for  their  daily  nourish- 
ment and  renovation.  In  this  process  it  must  suffer  a  variety  of  trans- 
formations, by  which  it  is  converted  into  the  different  albumenoid  mat- 
ters characteristic  of  muscular,  nervous,  glandular,  and  other  structures 
throughout  the  body. 

The  ingredient  next  in  abundance  isparaglobuline,  the  average  quan- 
tity of  which  is  about  one-half  that  of  the  albumen.  It  is  closely  allied 
to  albumen  in  its  chemical  relations,  and  no  doubt  also  in  its  physiolog- 
ical action ;  and  it  is  possible  that  either  one  of  these  substances  may 
be  an  intermediate  stage  of  production  or  metamorphosis  of  the  other. 
The  principal  distinction  between  them  is  that  paraglobuline  may  be 
thrown  down  by  the  addition  of  sodium  chloride  in  excess,  or  by  passing 
through  the  diluted  blood-serum  a  stream  of  carbonic  acid,  neither  of 
which  agents  has  any  effect  on  albumen.  As  both  substances  are  coag- 
ulable  by  heat,  they  are  solidified  together  on  raising  the  blood-serum  to 
a  temperature  of  72°  C. 

The  fibrinogen  of  the  plasma  is  the  substance  which  produces  the 
solid  fibrine  of  coagulated  blood.  It  is  difficult  to  obtain  in  the  fluid 
condition,  owing  to  the  rapidity  with  which  it  coagulates  when  blood 
is  withdrawn  from  the  circulation.  It  is  usually  separated,  in  the  form 
of  coagulated  fibrine,  by  stirring  freshly-drawn  blood  with  glass  rods  or 
a  bundle  of  twigs,  when  the  fibrine  solidifies  in  thin  layers  on  their 
surface.  It  at  first  contains,  entangled  with  it,  some  of  the  red  glob- 
ules with  their  coloring  matter;  but  these  and  other  foreign  substances 
may  be  removed  by  immersing  it  for  a  few  hours  in  running  water. 
It  is  then  a  mass  of  nearly  white  threads  and  flakes,  of  semi-solid  con- 
sistency, and  having  a  considerable  degree  of  elasticity. 

Examined  in  thin  layers,  it  has  a  fibroid  or  filamentous  texture.  Its 
filaments  are  colorless  and  elastic,  and  not  more  than  0.5  nimm.  in  diam- 
eter. They  lie,  for  the  most  part,  parallel  with  each  other,  and  this  is 
probably  their  arrangement  throughout  in  the  undisturbed  fil>rinoiis 
layer;  but  when  torn  up  for  microscopic  examination,  thev  are  in 
many  spots  interlaced  with  each  other  in  an  irregular  network.  In 
dilute  acetic  acid  they  become  swollen,  transparent,  and  fused  into  a 
homogeneous  mass,  but  do  not  dissolve1.  They  are  often  interspersed 


THE    BLOOD.  223 

with  minute  granules,  which  render  their  outlines  more  or  less  ob- 
scure. 

Once  coagulated,  fibrine  is  insoluble  in  water,  and  can  only  be  again 
liquefied  by  the  action  of  an  alkaline  or  strongly  saline  solution,  by  pro- 
longed boiling  at  a  very  high  temperature,  or  by  digesting  with  gastric 
juice  or  an  acidulated  solution  of  pepsine.  These  agents,  however,  pro- 
duce a  permanent  alteration  in  its  properties,  so  that  it  is  no  longer  the 
same  substance  as  before. 

The  quantity  of  fibrine  obtainable  from  the  blood  varies  in  different 
parts  of  the  body.  According  to  most  observers,*  venous  blood  in 
general  yields  less  fibrine  than  arterial  blood.  In  the  liver  and  the 
kidneys  its  disappearance  is  so  complete  that  little  or  none  is  to  be 
obtained  from  the  blood  of  tho  renal  and  hepatic  veins.  On  this 
account,  the  blood  in  the  large  veins  near  the  heart  is  more  deficient 
in  fibrine  than  in  those  at  a  distance ;  since  the  venous  blood  com- 
ing from  the  general  circulation,  and  containing  a  moderate  quantity, 
is  mingled,  on  approaching  the  heart,  with  that  of  the  renal  and  hepatic 
veins,  in  which  it  is  nearly  or  entirely  absent. 

A  certain  quantity  of  peptone  is  also  found  in  the  plasma,  derived 
from  the  products  of  digestion.  Its  quantity,  according  to  Robin, 
varies  from  1  to  4  parts  per  thousand.  As  it  is  absorbed  from  the 
intestine,  and  neither  accumulates  in  the  plasma  nor  appears  in  any  of 
the  excretions,  it  is  no  doubt  transformed  into  some  other  substance 
after  its  entrance  into  the  blood. 

The  fatty  matters  of  the  blood  are  in  largest  quantity  soon  after  the 
digestion  of  food  rich  in  oleaginous  substances.  At  that  period,  the 
emulsioned  fat  finds  its  way  into  the  .blood,  and  circulates  for  a  time 
unchanged  ;  communicating  to  the  serum,  when  very  abundant,  a  turbid 
or  whitish  appearance.  Afterward  it  gradually  disappears  from  the 
circulation,  being  either  deposited  in  the  fatty  tissues  or  transformed 
into  other  products  of  assimilation. 

The  mineral  salts  of  the  plasma  are  principally  sodium  and  potas- 
sium chlorides,  phosphates,  and  sulphates,  together  with  lime  and  mag- 
nesium phosphates.  Of  these  the  sodium  chloride  is  the  most  abundant, 
constituting  nearly  40  per  cent,  of  all  the  saline  ingredients.  The 
sodium  and  potassium  phosphates  are  important  for  the  alkalescence 
of  the  blood-plasma,  a  property  which  is  essential  to  the  functions  of 
nutrition,  and  even  to  the  immediate  continuance  of  life ;  since  it 
enables  the  plasma  to  absorb  carbonic  acid  in  the  capillary  circula- 
tion, and  return  it  to  the  lungs  for  elimination.  The  alkaline  carbon- 
ates also  take  part  in  the  production  of  this  alkalescence,  and  in  the 
herbivorous  animals  are  its  principal  cause  ;  while  in  the  carnivora  the 
phosphates  are  more  important  in  this  respect,  In  man,  under  an  ordi- 
nary mixed  diet,  both  the  phosphates  and  carbonates  are  present  in 
varying  proportion. 


Robin,  Le9ons  sur  les  Humeurs.     Paris,  1874,  pp.  137,  140,  172. 


224  FUNCTIONS    OF    NUTRITION. 

The  earthy  phosphates  of  the  plasma,  which  by  themselves  are  insol- 
uble in  alkaline  or  neutral  fluids,  are  held  in  solution  in  the  blood  by 
union  with  its  albuminous  ingredients. 

Coagulation  of  the  Blood. 

Within  a  few  moments  after  blood  has  been  withdrawn  from  the 
vessels,  it  presents  the  remarkable  phenomenon  of  coagulation  or  clot- 
ting. This  process  commences  at  nearly  the  same  time  throughout  the 
whole  mass,  which  becomes  first  somewhat  diminished  in  fluidity,  so 
that  its  surface  may  be  gently  depressed  with  the  end  of  the  finger 
or  a  glass  rod.  It  then  becomes  rapidly  thicker,  and  at  last  solidifies 
into  a  uniformly  red,  opaque,  gelatinous  mass,  which  takes  the  form 
of  the  vessel  in  which  the  blood  was  contained.  Coagulation  usually 
commences,  in  man,  in  from  ten  to  twelve  minutes  after  the  blood 
has  been  drawn,  and  is  completed  in  about  twenty  minutes.  In  most 
animals,  it  is  more  rapid  than  this,  taking  place  in  the  dog,  ox,  and 
sheep  often  within  five  minutes.  In  the  horse,  on  the  other  hand,  it  is 
exceptionally  slow,  requiring  a  longer  time  than  in  man. 

The  coagulation  of  the  blood  is  dependent  on  the  presence  of  its 
fibrine-producing  ingredient.  This  may  be  demonstrated  in  various 
ways.  First,  if  freshly  drawn  frog's  blood  be  mixed  with  a  solution 
of  sugar  of  one-half  per  cent.,  and  placed  on  a  filter,  the  blood-glob- 
ules will  be  retained ;  and  the  transparent  colorless  filtered  fluid  after 
a  time  coagulates  like  fresh  blood.  Secondly,  if  horse's  blood,  which 
coagulates  slowly,  be  drawn  from  the  veins  into  a  cylindrical  vessel 
and  allowed  to  remain  at  rest,  by  the  time  coagulation  takes  place  the 
blood-globules  will  have  partially  subsided,  leaving  at  the  surface  a 
layer  which  is  colorless  and  semi-transparent,  but  as  firmly  coagulated 
as  the  rest.  Thirdly,  if  horse's  blood,  freshly  drawn  into  such  a  ves.-cl, 
be  surrounded  by  .a  freezing  mixture,  and  kept  at  the  temperature  of 
0°  C.,  coagulation  is  suspended,  and  the  globules  sink  towards  the  bot- 
tom, leaving  a  colorless  fluid  above.  If  this  be  removed  by  decantation, 
and  allowed  to  rise  in  temperature  a  few  degrees,  it  coagulates  like  fresh 
blood. 

These  facts  show  that  the  blood-globules  take  no  direct  part  in 
coagulation ;  and  that,  when  present,  they  are  simply  entangled  in 
the  solidifying  clot. 

Finally,  if  the  freshly  drawn  blood  of  man,  or  of  any  warm-blooded 
animal,  be  stirred  with  a  bundle  of  twigs  or  glass  rods,  the  fibrine 
coagulates  in  comparatively  small  mass  on  the  surface  of  the  foreign 
bodies;  and  the  globules  entangled  in  it  may  be  washed  out  with- 
out changing  its  essential  character. 

It  is  the  fibrinogen,  therefore,  which,  by  its  coagulation,  induces  the 
solidification  of  the  entire  blood.  As  it  is  uniformly  distributed  through- 
out, when  coagulation  takes  place  its  filaments  entangle  in  thrir  nicshcs 
the  globules  and  albuminous  fluids  of  the  plasma.  A  very  snmll  quan- 
tity of  fibrine  is  sufficient  to  include  in  its  solidification  all  the  fluid  and 


THE    BLOOD.  225 

semi-fluid  ingredients  of  the  blood,  and  to  convert  the  whole  into  a 
jelly-like,  coagulated  mass. 

As  soon  as  the  coagulum  is  formed,  it  begins  to  contract,  increasing 
in  consistency  as  it  diminishes  in  size.  By  this  means  the  albuminous 
liquids  are  pressed  out  from  the  meshes  in  which  they  were  entangled. 
They  first  exude  upon  the  surface  as  isolated  drops,  which  soon  increase 
in  size  and  number.  After  a  time  they  coalesce  in  all  directions,  until 
the  whole  surface  is  covered  with  fluid.  The  clot  at  first  adheres  closely 
to  the  sides  of  the  vessel ;  but  as  contraction  goes  on,  it  separates,  and 
fluid  exudes  between  it  and  the  vessel.  This  continues  for  ten  or  twelve 
hours ;  the  clot  growing  constantly  smaller  and  firmer,  and  the  expressed 
fluid  more  abundant. 

The  globules,  owing  to  their  greater  consistency,  do  not  escape  with 
the  albuminous  fluids,  but  remain  entangled  in  the  coagulum.  At  the 
end  of  twelve  hours  the  blood  is  completely  separated  into  two  parts, 
namely,  the  clot,  a  red,  opaque,  semi-solid  mass,  consisting  of  fibrine 
and  blood-globules ;  and  the  serum,  a  transparent,  nearly  colorless  fluid, 
containing  the  watery,  albuminous,  and  saline  matters  of  the  plasma. 

The  change  of  the  blood  in  coagulation  may  be  expressed  as  follows : 

Before  coagulation  it  consists  of 

Fibrinogen, 
Albumen, 
1st.  GLOBULES  ;  and  2d.  PLASMA — containing  \  Paraglobuline, 

Water, 
x  Salts. 
After  coagulation  it  is  separated  into 

f  Albumen, 

(Fibrine  and  Paraglobuline. 

1st.  CLOT,  containing  \    '  ,  and  2d.  SERUM,  containing  \  w 

(^  LrioDuies  5  w  aiei , 

[  Salts. 

Conditions  favoring  or  retarding  Coagulation. — The  coagulation  of 
blood  is  influenced  by  various  physical  conditions.  In  the  first  place, 
it  is  suspended  by  a  freezing  temperature.  If  blood  be  drawn  into  a 
narrow  vessel  surrounded  by  a  freezing  mixture,  and  rapidly  cooled 
down  to  0°  C.,  coagulation  does  not  occur,  and  the  blood  remains  fluid 
so  long  as  the  temperature  is  at  this  point. 

Secondly,  coagulation  is  prevented  by  the  presence  of  certain  neutral 
salts  in  large  quantity.  If  fresh  blood  be  allowed  to  mingle  with  a 
concentrated  solution  of  sodium  sulphate,  no  coagulation  takes  place. 
This  is  not  because  the  coagulable  material  has  been  destroyed ;  since, 
if  the  mixture  be  diluted  with  six  or  seven  times  its  volume  of  water, 
so  as  to  reduce  its  concentration,  the  fibrine  solidifies  in  a  few  moments 
as  usual. 

Coagulation  of  the  blood  may  be  hastened  or  retarded  by  variations 
in  the  manner  of  its  withdrawal  from  the  veins,  or  in  the  surfaces  with 
which  it  comes  in  contact.  If  drawn  rapidly  from  a  large  orifice,  it 

P 


226  FUNCTIONS    OF    NUTRITION. 

remains  fluid  for  a  comparatively  long  time ;  if  slowly,  from  a  narrow 
orifice,  it  coagulates  quickly.  The  shape  and  structure  of  the  vessel 
into  which  it  is  received  also  exert  an  influence.  The  greater  the  surface 
over  which  the  blood  comes  in  contact  with  the  vessel,  the  more  is  coag- 
ulation hastened.  If  allowed  to  flow  into  a  tall,  narrow,  cylindrical 
vessel,  or  a  shallow  plate,  it  coagulates  more  rapidly  than  if  received 
in  a  hemispherical  bowl,  in  which  the  extent  of  surface  is  less,  in  pro- 
portion to  its  capacity.  For  the  same  reason,  coagulation  takes  place 
sooner  in  a  vessel  with  roughened  surface  than  in  one  which  is  smooth  ; 
and  blood  coagulates  most  rapidly  when  spread  out  in  thin  layers,  or 
entangled  in  cloths  or  sponges.  Hemorrhage,  accordingly,  continues 
longer  from  an  incised  than  from  a  lacerated  wound  ;  because  the  blood, 
in  flowing  over  the  ragged  edges  of  lacerated  tissues,  solidifies  upon 
them,  and  blocks  up  the  orifice. 

In  all  cases  there  is  an  inverse  relation  between  the  rapidity  of  coag- 
ulation and  the  firmness  of  the  clot.  When  coagulation  takes  place 
slowly,  the  clot  becomes  small  and  dense,  and  the  serum  is  abundant. 
When  rapid,  it  is  followed  by  imperfect  contraction  of  the  coagulum, 
and  incomplete  separation  of  the  seruni,  and  the  clot  remains  large,  soft, 
and  gelatinous. 

The  blood  coagulates  in  the  interior  of  the  vessels  after  stoppage  of 
the  circulation.  Under  these  circumstances  coagulation  takes  place 
less  rapidly  than  in  blood  withdrawn  from  the  body.  In  man,  as  a  rule, 
the  blood  is  found  coagulated  in  the  heart  and  large  vessels  from  twelve 
to  twenty-four  hours  after  death.  In  most  animals,  coagulation  occurs 
earlier  than  this,  usually  from  four  to  ten  hours  after  death. 

Coagulation  of  the  blood  takes  place  also  within  the  body,  during 
life,  from  local  arrest  or  impediment  of  the  circulation.  Blood  ex- 
travasated  into  the  connective  tissue,  the  substance  of  an  internal 
organ,  or  a  serous  cavity,  coagulates  after  a  short  time,  and  forms  a  clot 
which  takes  the  shape  of  the  cavity  occupied.  A  ligature,  placed  upon 
an  artery  in  the  living  subject,  produces  coagulation  above  the  ligatured 
spot.  The  clot  extends  from  the  ligature  backward  to  the  next  collateral 
branch,  that  is,  to  the  point  at  which  the  circulation  still  continues.  In 
an  aneurism  the  blood  in  the  dilated  portion  of  the  artery  coagulates  on 
the  inner  surface  of  the  sac.  In  these  cases,  as  well  within  as  outside  the 
body,  and  during  life  as  well  as  after  death,  stoppage  or  retardation  of  the 
circulatory  movement  induces,  after  a  time,  the  coagulation  of  the  blood. 

It  is  asserted,^  however,  that  simple  stoppage  of  the  local  circulation 
during  life  will  not  induce  coagulation,  unless  the  inner  membrane  of 
the  blood-vessel  be  wounded  or  irritated.  According  to  Burdon  San- 
derson, if  blood  be  imprisoned  in  the  jugular  vein  of  the  rabbit  by 
carefully  compressing  the  vessel  at  t\v<>  points  between  transverse  nee- 
dles, so  arranged  as  not  to  wound  or  bruise  the  vascular  coats,  it  will 
remain  fluid  in  this  situation  for  two  days;  while  if  ordinary  ligatures 
be  applied,  a  coagulum  is  formed  in  the  isolated  portion  of  the  vein. 

From  this  it  would  appear  that  some  injury  or  alteration  of  the 


THE    BLOOD.  227 

vascular  walls  is  an  element  in  the  exciting  cause  of  coagulation. 
It  is  of  course  impossible  to  withdraw  blood  from  the  system  without 
inflicting  such  an  injury ;  and  we  know  that  in  cases  of  phlebitis,  coagula- 
tion often  takes  place  within  the  affected  veins,  when  the  only  condition 
present  to  explain  it  is  the  inflammatory  alteration  of  the  vascular  walls. 

The  coagulation  of  fibrine  is  not  a  commencement  of  organization. 
It  is  simply  the  passage  of  one  of  the  ingredients  of  the  blood  from 
its  normal  condition  to  a  state  of  solidity.  The  coagulable  matter, 
when  solidified,  has  lost  its  natural  properties  as  a  constituent  of  the 
plasma,  and  they  cannot  afterward  be  restored.  The  clot,  therefore,  once 
formed,  even  within  the  body,  as  in  cases  of  ligature,  apoplexy,  or 
extravasation,  becomes  a  foreign  substance,  and  is  absorbed  by  the 
neighboring  parts  during  convalescence.  At  first  it  is  comparatively 
voluminous,  soft,  and  red.  Its  more  fluid  parts  are  then  taken  up,  and 
it  becomes  smaller  and  denser.  As  absorption  goes  on,  its  coloring 
matter  diminishes,  and  finally  disappears.  The  time  required  for  com- 
plete reabsorption  of  a  clot  varies,  according  to  its  size  and  situation, 
from  a  few  days  to  several  months. 

Nature  of  Coagulation.  —  The  coagulation  of  blood  has  been  the 
subject  of  much  laborious  investigation.  The  difficulty  of  understand- 
ing its  nature  depends  on  the  fact  that  the  blood,  which  continues  fluid 
under  normal  conditions  while  circulating  in  the  vessels,  solidifies 
promptly  and  inevitably  on  its  withdrawal.  It  is  evident  that  the 
solid  fibrine  which  we  obtain  after  coagulation  is  not  the  material  which 
was  present  beforehand  in  the  blood ;  but  that  it  has  been  produced, 
by  some  alteration,  from  a  preexisting  fluid  substance.  Any  theory  of 
the  process,  to  be  satisfactory,  must  explain  not  only  the  coagulable 
property  of  the  fibrine-producing  ingredient,  but  also  the  fluidity  of 
the  blood  in  its  natural  condition,  notwithstanding  that  it  contains  a 
material  so  ready  to  assume  the  solid  form.  It  is  unnecessary  to  con- 
sider the  former  theories  of  coagulation,  which  have  now  been  aban- 
doned as  inconsistent  with  known  facts.  It  is  not  due  to  the  cooling 
of  the  blood,  to  the  contact  of  air,  nor  to  the  escape  of  a  gaseous  sol- 
vent ;  since  it  will  occur  in  the  absence  of  all  these  conditions.  Of 
late  years,  the  only  views  on  this  subject  which  have  attracted  general 
attention  are  those  of  Denis,  in  which  coagulation  is  explained  by  the 
decomposition  of  a  previously  existing  substance,  and  those  of  Schmidt, 
which  attribute  it  to  the  union  of  two  substances  previously  distinct. 

According  to  Denis,  the  blood  contains  an  albuminous  matter,, 
termed  "  plasmine,"  in  the  proportion  of  25  parts  per  thousand.  When 
withdrawn  from  the  circulation,  it  separates  into  two  new  substances  ; 
namely,  fibrine  (3  parts  per  thousand)  which  coagulates,  and  paraglob- 
uline  (22  parts  per  thousand)  which  remains  fluid.  The  basis  for  this 
theory  is  that  if  fresh  blood  be  drawn  into  a  concentrated  solution  of 
sodium  sulphate,  to  prevent  its  coagulation,  and  sodium  chloride  be 
added  to  the  mixture  in  the  proportion  of  ten  per  cent,  it  throws 
down  a  white,  pasty  substance,  which  represents  25  parts  per  thousand 


228  FUNCTIONS    OF    NUTRITION. 

of  the  oriu-inal  plasma.  This  substance  is  the  so-called  "plasmine;" 
and  if  redissolved  by  the  addition  of  water,  its  solution  coagulates, 
yielding  3  parts  of  a  solid  matter,  like  fibrine,  and  22  parts  of  a  liquid 
substance,  having  the  properties  of  paraglobuline.  The  albumen  of  the 
plasma  (53  parts  per  thousand)  remains  in  the  sodium  sulphate  solu- 
tion, not  having  been  precipitated  by  the  addition  of  sodium  chloride. 

This  theory  is  defective,  because  the  material  termed  "plasmine," 
may  be,  from  the  first,  a  mixture  of  two  different  substances,  one  coag- 
ulable  and  the  other  not  so,  but  both  precipitable  from  the  sodium 
sulphate  solution  by  sodium  chloride.  In  that  case,  it  would  not  facili- 
tate the  explanation  of  the  process.  In  point  of  fact  we  know  that  both 
the  fibrine-producing  substance  and  paraglobuline  may  be  thrown  down 
from  their  solutions  by  the  addition  of  sodium  chloride  in  excess. 

According  to  the  theory  of  Schmidt,  the  coagulable  fibrine  is  pro- 
duced by  the  union  of  two  previously  existing  substances,  neither  being 
coagulable  by  itself.  One  of  these  substances  is  fibrinogen,  present  in 
the  blood  in  small  quantity ;  the  other  is  paraglobuline,  present  in  large 
quantity.  When  the  fibrinogen,  therefore,  has  all  been  converted  into 
coagulated  fibrine,  there  still  remains  in  the  serum  a  surplus  of  para- 
globuline, which  may  cause  coagulation  in  other  liquids,  provided  they 
contain  fibrinogen.  The  liquid  usually  employed  to  demonstrate  this 
property  is  that  of  hydrocele,  which  does  not  coagulate  spontaneously, 
but  may  sometimes  be  made  to  do  so  by  the  addition  of  blood-serum. 

It  was  found,  however,  that  both  fibrinogen  and  paraglobuline  migli. 
be  present  in  a  liquid,  and  yet  fail  to  produce  coagulation.  The  author* 
of  the  theory  therefore  recognized  the  existence  of  a  third  substance, 
the  "  fibrine  ferment,"  which  was  essential  to  induce  the  combination 
of  the  other  two.  According  to  this  view,  fibrinogen  and  paraglobuline 
both  exist  in  the  blood  while  circulating  in  the  vessels ;  and,  when  they 
unite,  supply  the  material  for  the  coagulated  fibrine.  But  the  ferment 
which  excites  their  combination  only  appears  in  the  blood  during  or 
after  its  withdrawal.  It  may  then  be  extracted  by  the  process  already 
described  (p.  81). 

There  is  no  doubt  in  regard  to  the  existence  and  character  of  the 
fibrine-ferment.  Its  mode  of  operation  is  analogous  to  that  of  other 
organic  ferments.  In  the  first  place  it  acts  in  very  small  quantity  in 
proportion  to  the  amouut  of  coagulation  produced.  Secondly,  its  action 
is  confined  within  certain  limits  of  temperature,  being  retarded  by  cold, 
and  permanently  arrested  by  the  heat  of  boiling  water.  Thirdly, 
though  precipitable  by  alcohol,  it  is  not  destroyed  by  this  substance, 
lnil  si  ft  IT  precipitation  may  be  redissolved  in  water,  with  its  properties 
unchanged.  Fourthly,  after  inducing  coagulation,  it  still  remains  in 
tin-  fluid  separated  by  filtration,  and  may  be  again  repeatedly  used  for 
the  same  purpose,  with  only  a  very  slow  diminution  of  its  activity. 
This  shows  that  it  does  not  contribute  by  its  substance  to  the  coagu- 

*  Archiv  fiir  die  gesammte  Physiologic.     Bonn,  1872,  Band  vi.,  p.  413. 


THE    BLOOD.  229 

lated  fibrine,  being  efficient  rather  by  its  presence,  after  the  manner 
of  the  ferments. 

But  there  is  reason  to  believe  that  the  fibrine-ferment,  in  inducing 
coagulation,  acts  only  on  the  fibrinogen,  and  that  paraglobuline  takes 
no  part  in  the  process.  According  to  Fredericq*  the  quantity  of  fibrine 
obtainable  from  a  solution  of  fibrinogen  of  known  strength,  is  never 
greater  than  that  of  the  fibrinogen  itself,  coagulated  by  heat.  This 
would  indicate  that  the  fibrinogen  alone  supplies  the  material  of  the 
coagulated  fibrine,  by  a  molecular  change  in  its  own  substance,  like  the 
caseine  of  milk  when  coagulated  by  rennet.  Hammarstenf  has  further- 
more satisfied  himself  that  when  solutions  of  paraglobuline  induce 
coagulation  in  liquids  containing  fibrinogen,  they  owe  this  property  to 
small  quantities  of  ferment  with  which  they  are  contaminated ;  and  by 
using  special  precautions  in  their  purification,  he  has  found  that  solu- 
tions of  fibrinogen  will  coagulate  completely  on  the  addition  of  the  fer- 
ment, when  neither  liquid  contains  any  trace  of  paraglobuline,  herno- 
globine,  or  serum-albumen. 

The  coagulation  of  fibrinogen  is,  therefore,  without  doubt  due  to  the 
action  of  a  ferment.  The  fibrinogen,  as  it  exists  in  the  circulating 
blood,  is  not  coagulable ;  and  it  becomes  so  only  by  contact  with  the 
substance  which  produces  its  alteration.  The  only  remaining  question 
is  in  regard  to  the  source  of  this  ferment,  when  blood  is  withdrawn  from 
the  vessels  or  coagulates  in  their  interior.  The  evidence  appears  to 
show  that  it  comes  from  the  divided  or  injured  vascular  coats,  or  from 
the  interstitial  spaces  beyond.  The  minute  quantity  necessary  to  effect 
coagulation  may  be  exuded  from  a  wounded  surface,  however  small ; 
and  after  death  it  may  slowly  transude  through  the  membranes,  like 
the  coloring  matters  and  serous  fluids  of  the  body.  But  the  place  and 
mode  of  its  production  can  hardly  be  determined  with  certainty,  until 
its  composition  and  physical  properties  are  fully  known. 

Usefulness  of  Coagulation. — Although  the  coagulating  material  of 
the  blood,  owing  to  its  small  quantity,  does  not  seem  to  take  a  large 
share  in  nutrition,  it  is  still  an  important  ingredient  of  the  circulating 
fluid.  It  is  this  substance  which  effects  the  arrest  of  hemorrhage  from 
divided  or  ruptured  blood-vessels.  Whenever  a  wound  is  made  in 
vascular  tissues,  the  blood  at  first  flows  freely  from  the  external  orifice. 
But  a  portion  soon  coagulates  on  the  edges  of  the  wound,  and  after  a 
time  its  successive  deposits  obstruct  the  orifice,  and  prevent  further 
hemorrhage.  For  wounds  of  moderate  size,  in  which  only  veins  and 
capillaries,  or  small  arteries,  have  been  divided,  it  is  sufficient  to  com- 
press the  wound  and  to  keep  its  edges  in  contact  for  fifteen  or  twenty 
minutes.  By  this  time  the  thin  layer  of  blood  between  the  wounded 
surfaces  has  coagulated,  and  when  compression  is  removed  hemorrhage 
does  not  reappear.  If  a  large  artery  be  opened,  the  force  with  which 
the  blood  is  expelled  prevents  local  coagulation,  or  may  detach  the 

*  Hoppe-Seyler,  Physiologische  Chemie.     Berlin,  1879,  p.  416. 
f  Archiv  fur  die  gesamrate  Physiologic.     Bonn,  1879,  Band  xix.,  pp.  563,  581. 


230  FUNCTIONS    OF    NUTRITION. 

coagula  after  they  are  formed.  In  such  cases  the  surgeon  places  a 
ligature  upon  the  wounded  artery,  and  in  this  way  controls  the 
hemorrhage.  But  the  ligature  is  only  a  means  of  applying  compres- 
sion for  a  longer  time,  and  is  still  temporary,  as  it  must  finally  come 
away  by  ulceration  through  the  coats  of  the  vessel.  The  essential  ob- 
stacle to  the  flow  of  blood  in  a  ligatured  artery  is  the  coagulum  formed 
in  the  vessel  behind  the  ligature ;  which,  when  the  ligature  is  detached 
by  ulceration,  has  become  sufficiently  dense  and  adherent  to  resist  the 
impulse  of  the  blood. 

The  importance  of  coagulation  in  this  respect  is  shown  by  the  diffi- 
culties which  follow  where  it  is  deficient.  In  some  cases  of  the  ligature 
of  large  arteries,  in  patients  exhausted  by  injury  or  loss  of  blood,  when 
the  ligature  comes  away  the  bleeding  begins  again,  no  internal  clot 
having  been  formed ;  and  a  second  ligature,  applied  above  the  situation 
of  the  former  one,  is  again  followed,  by  secondary  hemorrhage.  In 
certain  persons  there  appears  to  be  a  congenital  deficiency  of  the 
coagulating  ingredient  of  the  blood,  a  peculiarity  sometimes  observed 
in  several  members  of  the  same  family ;  and  in  these  cases,  any  slight 
wound,  or  trivial  surgical  operation,  may  be  followed  by  long-continued 
or  fatal  hemorrhage. 

Entire  Quantity  of  Blood  in  the  Body. — The  estimation  of  the 
quantity  of  blood  in  the  living  body  is  surrounded  with  difficulties. 
The  earliest  and  simplest  method  adbpted  was  by  suddenly  dividing 
all  the  vessels  of  the  neck  in  a  living  animal  and  collecting  the  blood 
which  escaped.  But  this  method  is  faulty,  since  the  flow  of  blood 
ceases,  in  such  an  experiment,  not  because  the  whole  of  it  has  been 
discharged,  but  because  coagula  have  formed  about  the  divided  vessels, 
and  because  the  heart's  action  begins  to  fail  before  the  vascular  system 
is  empty.  A  certain  quantity  of  blood  always  remains  in  the  body  after 
death  by  hemorrhage  ;  amounting  sometimes  to  over  25  per  cent,  of  the 
entire  mass.  The  animal  therefore  dies  before  he  has  lost  quite  three- 
fourths  of  the  circulating  fluid. 

Of  the  other  methods  which  have  been  adopted  there  are  none  abso- 
lutely free  from  possible  sources  of  error.  The  best  are  those  by 
which,  after  all  the  blood  is  discharged  which  escapes  spontaneously 
from  divided  vessels,  the  circulatory  system  is  injected  with  a  weak 
saline  solution,  until  the  fluid,  after  traversing  the  vascular  channels, 
returns  colorless.  The  quantity  of  blood  thus  washed  out  is  then 
n-i-crtained  by  comparing  the  fluid  of  injection  with  a  watery  dilution 
of  blood  of  known  strength. 

The  most  accurate  process  is  that  employed  by  Steinberg,*  who,  after 
bleeding  the  animal  to  death,  injected  the  aorta  with  a  watery  solution 
of  sodium  chloride,  of  one-half  per  cent.,  until  the  fluid  of  injection  re- 
turned colorless.  The  whole  of  it  being  then  mingled,  the  heinoglobine 
which  it  contained  was  determined  as  follows  by  the  spectroscopic  b 
Equal  quantities  of  pure  blood,  in  two  similar  test-tubes,  were  diluted. 

*  Archiv  fur  die  gesuimiite  Physiologic.     Bonn,  1873,  Ikind  vii.,  p.  101. 


THE    BLOOD.  231 

one  of  them  with  pure  water,  the  other  with  the  fluid  of  injection,  until 
each,  placed  before  the  slit  of  the  spectroscope,  just  allowed  the  green 
light  of  the  spectrum  to  be  visible.  From  the  relative  quantities  of  the 
two  liquids  needed  to  produce  this  result,  the  amount  of  hemoglobine, 
and  consequently  of  blood,  extracted  by  the  injection  could  be  calculated. 
This  quantity,  added  to  that  which  had  escaped  spontaneously  from 
the  vessels,  gave  the  entire  amount  of  blood,  as  follows : 

QUANTITY  OF  BLOOD,  AS  COMPARED  WITH  THE  BODILY  WEIGHT. 

In  Dogs,  from  8.00  to  8.93  per  cent. 

"  Cats,  "      8.40  "  9.61        " 

"  Guinea-pigs,    "      8.13  "  8.33       " 

"  Eabbits,  "      7.50  "  8.13       " 

There  is  evidence  that  the  quantity  of  blood  varies  in  the  same 
animal,  according  to  various  bodily  conditions,  and  especially  the 
digestive  process.  Steinberg  found  that  in  the  cat,  while  fasting,  the 
percentage  of  blood  wras  reduced  from  8.40  to  5.61  per  cent.  Ber- 
nard* observed  that  if  two  animals  of  the  same  weight,  one  in  full 
digestion  and  the  other  fasting,  be  suddenly  decapitated,  the  quantity 
of  blood  discharged  from  the  former  is  greater  than  that  from  the 
latter.  He  has  also  shown  that,  in  a  rabbit  during  digestion,  twice  as 
much  blood  can  be  withdrawn  without  causing  death,  as  in  one  of  the 
same  weight  in  the  fasting  condition.  The  volume  of  blood  in  the  body 
fluctuates,  therefore,  within  certain  limits,  with  the  introduction  of 
nutritious  matter  by  digestion  and  its  expenditure  during  the  interval. 

The  most  satisfactory  determination  of  the  quantity  of  blood  in  man 
is  that  by  Weber  and  Lehmann.')'  These  observers  operated  on  two 
criminals  executed  by  decapitation  ;k  the  methods  and  results  being 
essentially  the  same  in  both.  In  one  case,  the  body  weighed  before 
decapitation  60.14  kilogrammes;  and  the  blood  which  escaped  sponta- 
neously amounted  to  5540  grammes.  To  estimate  the  quantity  remain- 
ing in  the  vessels,  the  experimenters  injected  the  arteries  of  the  head 
and  trunk  with  water  until  it  returned  from  the  veins  of  a  pale  red 
or  yellow  color,  collected  the  fluid  thus  returned,  and  ascertained  the 
amount  of  its  solid  matter.  The  result  was  as  follows : 

Blood  which  escaped  from  the  vessels     .         .         5540  grammes. 
"  remained  in  the  body  .         .         1980       " 

Entire  quantity,    .         .         7520       " 

The  blood,  accordingly,  amounted  during  life  to  12.54  per  cent,  of  the 
bodily  weight.  Bischoff,  in  a  similar  observation,  in  1855,  found  it 
only  about  8  per  cent.  As  in  Steinberg's  experiments  the  quantity  of 
blood  in  the  cat  also  varied  by  50  per  cent,  above  the  minimum,  it 
will  probably  be  near  the  truth  to  estimate  its  average  quantity  in  the 
human  subject  at  about  10  per  cent,  of  the  bodily  weight ;  and  a  man 
weighing  65  kilogrammes  (143  pounds  avoirdupois)  would  therefore 
have  6500  grammes,  or  a  little  over  14  pounds  of  blood. 

*  Le9ons  sur  les  Liquides  de  1'Organisme.     Paris,  1859,  tome  i.,  p.  419. 

f  Physiological  Chemistry,  Cavendish  edition.     London,  1853,  vol.  ii.,  p.  269. 


CHAPTER  IV. 
RESPIRATION. 

THE  most  constant  phenomenon  presented  by  living  organisms,  both 
animal  and  vegetable,  is  the  absorption  of  oxygen.  This  sub- 
stance, either  in  the  gaseous  form  as  a  constituent  of  the  atmosphere, 
or  dissolved  in  water  or  other  liquids,  is  indispensably  requisite  for  the 
manifestation  of  vital  phenomena.  Oxygen  is  diffused  everywhere 
over  the  surface  of  the  earth,  forming  rather  more  than  one-fifth  part 
of  the  volume  of  the  atmosphere,  and  exists  in  solution  in  greater  or 
less  abundance  in  the  water  of  springs,  rivers,  lakes,  and  seas.  Animals 
and  plants,  accordingly,  whether  living  in  the  air  or  in  the  water,  are 
surrounded  by  media  in  which  this  substance  is  present.  Even  para- 
sitic organisms,  inhabiting  other  living  bodies,  and  the  foetus  during 
intra-uterine  life,  though  not  immediately  in  contact  with  oxygen,  are 
supplied  with  nutritious  fluids  which  have  themselves  been  exposed  to 
its  influence.  Respiration  consists  in  the  process  by  which  oxyiren 
penetrates  the  substance  of  living  organisms,  and  the  changes  which 
accompany  or  follow  its  introduction. 

Respiration  in  Vegetables. — In  regard  to  vegetables,  a  distinction  is 
to  be  made  between  respiration  and  the  absorption  of  gaseous  matter 
for  the  production  of  organic  material.  All  green  plants,  under  the 
influence  of  solar  light,  absorb  carbonic  acid  and  water ;  partially  deox- 
idizing these  substances,  to  form,  with  their  remaining'  elements,  starch, 
cellulose,  and  fat.  The  oxygen  thus  separated  is  exhaled  in  a  free  form ; 
while  an  accumulation  of  organic  material  takes  place  in  the  vegetable 
fabric,  which  thus  increases  in  substance,  and  may  afterward  serve  for 
the  nutrition  of  animals.  This  process,  therefore,  is  not  one  of  respi- 
ration, but  of  organic  production.  It  is  peculiar  to  vegetables,  since 
animals  have  no  power  to  produce  organic  material,  and  depend  upon 
vegetables  for  their  supply  of  food. 

Animals,  on  the  other  hand,  consume  the  organic  material  thus  pro- 
duced, at  the  same  time  absorbing  oxygen  and  exhaling  carbonic  acid 
and  water.  In  this  respect  animal  and  vegetable  life  stand  in  a  com- 
plementary relation  to  each  other.  Vegetables  produce  organic  matter 
by  deoxidation;  animals  consume  it  with  the  phenomena  of  oxidation. 

But  this  apparent  opposition  only  exists  because  plants  have  tin- 
special  power  of  producing  organic  matter,  by  which  they  become  a 
source  of  nourishment  for  nnimals.  The  organic  substances  so  pro- 
duced do  not  immediately  take  part  in  the  active  phenomena  even  of 
vegetable  life.  They  are,  on  the  contrary,  deposited  in  a  quiescent 

283 


RESPIRATION.  233 

form  as  reserve  material,  to  be  afterward  transformed  and  assimilated 
by  the  plant,  or  consumed  by  animals.  In  vegetables,  as  well  as  in 
animals,  a  true  respiration  also  takes  place,  marked  in  both  instances 
by  the  absorption  of  oxygen.  The  deoxidizing  process,  by  which 
organic  matter  is  produced,  occurs  only  in  green  vegetables,  under  the 
influence  of  solar  light ;  but  the  absorption  of  oxygen  is  a  constant 
phenomenon,  taking  place  in  both  green  and  colorless  plants,  in  dark- 
ness as  well  as  in  the  light. 

The  active  phenomena  of  vegetation,  moreover,  are  dependent  on 
the  absorption  of  oxygen,  and  cannot  go  on  without  it.  When  the 
starch  stored  up  in  a  seed  becomes  liquefied  and  converted  into  sugar, 
and  germination  begins,  the  absorption  of  oxygen  is  necessary  to  its 
continuance.  This  is  the  case  not  only  in  germinating  seeds,  but  also 
in  expanding  leaf  and  flower  buds,  all  of  which  consume  in  a  short 
period  several  times  their  volume  of  oxygen.  The  processes  of  germi- 
nation, growth,  and  flowering,  as  well  as  the  intra-cellular  movement 
of  the  vegetable  plasma,  the  motions  of  the  sensitive-plant  in  response 
to  stimulus,  and  certain  periodical  movements  of  the  leaves  in  other 
species,  all  cease  in  an  atmosphere  deprived  of  oxygen.*  The  function 
of  respiration  is  accordingly  essential  to  every  form  of  vital  activity. 

Organs  of  Respiration. 

Respiration  is  very  active  in  the  mammalians  and  birds,  less  so  in 
reptiles  and  fishes  ;  and  in  different  classes  the  organs  by  which  it  is 
accomplished  vary  in  size  and  FlG  50 

structure  according  to  the  activity  ^  ^ 

of  the  function.    Its  requisite  con-  fmmm    /j& 

ditions   are   that   the  circulating 
fluid  be  exposed  in  some  way  to 
the  influence  of  the  atmosphere 
or  of  an  aerated  fluid.    The  respi- 
ratory apparatus  consists  essen- 
tially of  a  moist  and  permeable 
respiratory  membrane,  with  blood- 
vessels On  one   side  and  air   or  an       '    HEAD  AND  GILLS  OF  MKNOBRANCHUS. 
aerated  fluid  on  the  other.     The  blood  and  the  air,  consequently,  do 
not  come  in  direct  contact  with  each  other,  but  absorption  and  exhala- 
tion take  place  through  the  intervening  membrane. 

In  most  aquatic  animals,  the  respiratory  organs  have  the  form  of 
gills;  that  is,  vascular  prolongations  of  the  integument  or  mucous 
membrane,  which  are  bathed  in  the  surrounding  water.  In  Meno- 
branchus  (Fig.  50)  the  gills  are  external  feathery  tufts  on  the  sides  of 
the  neck,  connected,  through  lateral  fissures,  with  the  mucous  mem- 
brane of  the  pharynx.  Each  filament  consists  of  a  fold  of  mucous 


*  Mayer,  Lehrbnch  der  Agrikultur-Chemie.    Heidelberg,  1871,  Band  i.,  pp.  91,  95. 
Hoppe-Seyler,  Physiologische  Chemie.     Berlin,  1877,  p.  171. 


234 


FUNCTIONS    OF    NUTRITION. 


Fm.  51. 


membrane,  containing  a  network  of  capillary  blood-vessels.     The  appa- 
ratus is  supplied  with  a  cartilaginous  framework  and  a  set  of  mu- 

by  which  the  gills  are  kept  in  motion,  and  thus 
brought  in  contact  with  fresh  portions  of  the  aerated 
fluid. 

In  terrestrial  and  air-breathing  animals,  the  rcspi- 
A  ratory  apparatus  is  situated  internally,   under  the 
S]  form  of  lungs.     In  salamanders  and  newts,  the  lungs 
g  are  cylindrical  sacs,  communicating  anteriorly  with 
y  the  pharynx,  and  terminating  by  rounded  extremities 
at  the  posterior  part  of  the  abdomen.     The  air,  forced 
into  them  from  the  pharynx,  is  after  a  time  regurgi- 
tated, to  make  room  for  a  fresh  supply. 

In  frogs,  turtles,  and  serpents,  the  lung  is  divided 
by  incomPlete  partitions  into  smaller  cavities  or 
"cells."  The  cells  all  communicate  with  the  cen- 
tral pulmonary  cavity ;  and  the  partitions  between  them  are  vascular 
folds  of  the  lining  membrane.  (Fig.  51.)  By  this  arrangement  a 

FIG.  52. 


LUNG    OF    FROG,    cut 


HUMAN  LARYNX,  TRACHEA,  BRONCHI  AND  LUNOS;  showing  the  ramifications  <if  the  bronchi,  and 
division  of  the  lungs  into  lobulrs. 

in-cuter  extent  of  pulmonary  surface  is  presented  to  the  air,  and  the 
aeration  of  the  blood  takes  place  with  a  corresponding  rapidity. 

In  the  warm-blooded  animals,  the   lungs  arc  constructed  on  a  plan 
essentially  similar  to  the  above,  differing  from  it  only  in  the  greater 


RESPIRATION.  235 

extent  to  which  the  pulmonary  cavity  is  subdivided.  In  man  (Fig. 
52)  the  respiratory  apparatus  begins  with  the  larynx,  communicating, 
through  the  glottis,  with  the  pharynx.  Then  follows  the  trachea,  a 
membranous  tube  with  cartilaginous  rings,  dividing  into  the  right  and 
left  bronchi.  These  divide  in  turn  into  secondary  and  tertiary  bronchi; 
the  subdivision  continuing,  and  the  bronchial  tubes  growing  con- 
stantly smaller  and  more  numerous.  As  they  diminish  in  size,  the 
tubes  grow  more  delicate  in  structure,  and  the  cartilaginous  rings  and 
plates  disappear  from  their  walls.  When  finally  reduced  to  a  diameter 
of  0.3  millimetre,  they  are  composed  only  of  a  thin  membrane,  lined 
with  pavement  epithelium,  resting  upon  an  elastic  fibrous  layer.  They 
are  then  known  as  the  "  ultimate  bronchial  tubes." 

Each  ultimate  bronchial  tube  terminates  in  a  pyramidal-shaped  islet 

FIG.  53.  FIG.  54. 


SINGLE  LOBULE  OF  HUMAN  LUNG.— a.  Ulti-       NETWORK  OF  CAPILLARY  BLOOD-VESSKLS  in  the 
mate  bronchial  tube.    6.  Cavity  of  lobule.  Pulmonary  Vesicles  of  the  Horse. — a.  Cavity  of 

c,  c,  c.  Pulmonary  vesicles.  Vesicle,  with  capillary  plexus,    b.  Pulmonary 

blood-vessels,  supplying  capillary  plexus.  (Frey.) 

of  pulmonary  tissue,  about  2  millimetres  in  diameter,  termed  a  "  pul- 
monary lobule."  Each  lobule  may  be  considered  as  representing  the 
frog's  lung  in  miniature.  It  consists  of  a  vascular  membrane  in  the 
form  of  a  sac,  the  cavity  of  which  is  divided  into  secondary  compart- 
ments bv  thin  partitions  projecting  from  its  inner  surface.  These 
secondary  cavities  are  the  "pulmonary  vesicles."  They  have,  ac- 
cording to  Kolliker,  an  average  diameter  of  about  0.25  millimetre; 
but  owing  to  the  distensibility  and  elasticity  of  their  walls,  they  are 
capable  of  dilating  to  double  or  triple  their  former  size,  and  returning 
to  their  original  dimensions  when  the  distending  force  is  removed. 
There  is  reason  to  believe  that  during  life  they  alternately  expand 
and  retract,  as  the  lungs  are  filled  and  emptied  with  the  movements 
of  respiration. 

Each  vesicle  is  surrounded  by  capillary  blood-vessels,  which  penetrate 
its  partition  walls  and  are  thus  exposed  on  both  sides  to  the  influence 
of  the  air  in  the  pulmonary  cavities.  The  abundant  elastic  tissue,  in 
the  walls  of  the  vesicles,  and  in  the  interlobular  spaces,  gives  to  the 


236  FUNCTIONS    OF    NUTRITION. 

lungs  their  property  of  resiliency.  The  pavement  epithelium  lining 
the  ultimate  bronchial  tubes  extends  into  the  lobules  and  vesicles, 
forming,  according  to  Kolliker,  a  continuous  investment  of  their  in- 
ternal surface. 

The  extensive  involution  of  the  respiratory  membrane,  resulting 
from  the  multiplication  of  the  bronchial  tubes  and  vesicles,  in  the 
lungs  of  man  and  mammalians,  increases  in  a  high  degree  the  activity 
of  respiration ;  since  the  blood  in  the  capillary  vessels,  distributed  in 
thin  layers  over  so  large  a  surface,  in  immediate  proximity  to  the  air 
in  the  pulmonary  cavities,  is  placed  under  the  most  favorable  conditions 
for  rapid  arterialization. 

Movements  of  Respiration. 

The  air  in  the  pulmonary  lobules  and  vesicles,  being  used  for  the 
arterialization  of  the  blood,  is  rapidly  altered  in  composition,  and 
requires  to  be  replaced  by  a  fresh  supply.  Its  renewal  is  effected  by 
alternate  movements  of  expansion  and  collapse  of  the  chest,  following 
each  other  in  regular  succession,  known  respectively  as  the  "  movement 
of  inspiration,"  and  the  "  movement  of  expiration." 

Movement  of  Inspiration. — The  expansion  of  the  chest  is  produced 
by  two  sets  of  muscles,  namely,  the  diaphragm  and  the  intercostals. 
The  diaphragm  is  a  vaulted  muscular  sheet,  forming  the  floor  of  the 
thorax,  its  edges  being  attached  to  the  lower  extremity  of  the  sternum, 
the  inferior  costal  cartilages,  the  borders  of  the  lower  ribs,  and  the 
bodies  of  the  lumbar  vertebrae,  whence  its  fibres  run  upward  and 
inward,  to  the  triangular  tendinous  expansion  at  its  centre.  In  the 
relaxed  condition,  its  convexity  rises  into  the  chest,  as  high  as  the  1<  -\ •<•! 
of  the  fifth  rib.  When  its  muscular  fibres  contract,  they  draw  its  cen- 
tral tendon  downward,  depressing  the  abdominal  organs,  and  enlarging 
the  cavity  of  the  chest  in  a  vertical  direction.  At  the  same  time1,  by 
the  contraction  of  the  intercostal  muscles,  the  ribs  are  drawn  upward 
and  outward,  rotating  upon  their  articulations  with  the  spinal  column, 
and  expanding  the  chest  from  side  to  side.  The  sternum  also  rises 
slightly  and  increases  to  some  extent  the  antero-posterior  diameter  of 
the  thorax.  By  these  changes,  the  cavity  of  the  lungs  is  enlarged  in 
every  direction,  and  the  air  penetrates,  by  the  force  of  aspiration, 
through  the  trachea  and  bronchial  tubes,  to  the  pulmonary  lobules  and 
vesicles. 

The  action  of  the  respiratory  muscles  is  indicnted  externally  by  two 
different  motions,  namely,  the  expansion  of  the  chest,  due  to  the  inter- 
costals, and  the  protrusion  of  the  abdomen,  caused  by  the  descent  of 
the  diuphrngm.  In  children,  as  well  as  in  the  adult  male,  under  ordi- 
nary conditions,  the  diaphniirm  performs  most  of  the  work,  and  the 
movements  of  the  abdomen  are  the  only  ones  especially  noticeable. 
Any  unusual  exertion,  however,  produ'-es  ;m  incrensed  expansion  of  the 
chest;  and  the  movement  of  the  ribs  becomes  more  plainly  visible  alter 


RESPIRATION.  237 

walking  or  running.  In  the  female,  the  movements  of  the  chest,  par- 
ticularly of  its  upper  half,  are  habitually  more  prominent  than  those  of 
the  abdomen ;  and  this  difference  in  the  mechanism  of  respiration  is 
characteristic  of  the  sexes. 

In  certain  abnormal  conditions  the  activity  of  either  the  intercostal 
muscles  or  the  diaphragm  may  be  separately  suspended,  leaving  the 
work  of  respiration  to  be  performed  by  the  remaining  set  of  muscles. 
If  the  intercostals  be  paralyzed  by  injury  of  the  spinal  cord  in  the 
lower  cervical  or  upper  dorsal  region,  the  thorax  remains  quiescent, 
while  the  protrusion  of  the  abdomen  is  increased  to  a  corresponding 
degree.  This  mode  of  breathing  is  called  abdominal  respiration. 

In  cases  of  peritonitis,  on  the  other  hand,  the  movements  of  the 
diaphragm  are  restrained,  owing  to  the  tenderness  of  the  inflamed  sur- 
face. This  is  known  as  thoracic  respiration  ;  since  the  expansion  of 
the  chest  becomes  more  active  than  usual,  and  is  the  only  visible  move- 
ment performed. 

Movement  of  Expiration. — After  inspiration  is  accomplished  and 
the  lungs  are  filled  with  air,  the  diaphragm  and  intercostal  muscles 
relax,  and  a  passive  movement  of  expiration  takes  place,  by  which  the 
pulmonary  cavity  is  partially  emptied.  It  is  mainly  accomplished  by 
the  elastic  reaction  of  the  lung  tissue,  which  compresses  the  pulmonary 
lobules  and  vesicles,  and  expels  a  portion  of  the  contained  air.  This 
elasticity  is  readily  shown  by  removing  the  lungs  from  a  recently  killed 
animal,  distending  them  by  insufflation  through  the  trachea,  and  then 
allowing  them  to  collapse.  They  react,  under  these  circumstances,  with 
sufficient  power  to  expel  the  larger  portion  of  the  injected  air.  Other 
organs,  during  life,  aid  in  the  process.  ^The  elastic  costal  cartilages, 
slightly  twisted  in  inspiration  by  the  elevation  of  the  ribs,  resume 
their  original  form  in  expiration,  and,  by  drawing  the  ribs  downward, 
compress  the  thorax.  Lastly,  the  abdominal  organs,  displaced  by  the 
descent  of  the  diaphragm,  are  forced  backward  by  the  elasticity  of  the 
abdominal  walls  and  of  their  own  fibrous  attachments,  carrying  the 
relaxed  diaphragm  before  them.  By  the  recurrence  of  these  two  move- 
ments, of  inspiration  and  expiration,  fresh  portions  of  air  are  alternately 
introduced  into  and  expelled  from  the  pulmonary  cavity. 

All  the  air  in  the  lungs,  however,  is  not  changed  at  each  movement. 
A  considerable  quantity  remains  behind  after  the  most  complete  expira- 
tion ;  and  even  when  the  lungs  have  been  removed  from  the  chest, 
they  still  contain  a  certain  volume  of  air,  which  cannot  be  displaced  by 
any  violence  short  of  disintegrating  the  pulmonary  tissue.  Only  a 
comparatively  small  portion  of  the  air,  therefore,  passes  in  and  out 
with  each  respiratory  movement ;  and  its  complete  renewal  will  require 
several  successive  respirations.  The  relation  in  quantity  between  the 
air  changed  at  each  respiration  and  that  contained  in  the  chest  varies 
with  different  conditions  ;  but  the  average  results  obtained  by  different 
observers  show  that,  in  general,  the  volume  of  the  inspired  and  expired 
air  is  from  10  to  13  per  cent,  of  the  whole  contents  of  the  pulmonary 


238 


FUNCTIONS    OF    NUTRITION. 


cavity.     Thus  it  will  need  from  eight  to  ten  respirations  entirely  to 
renovate  the  air  in  the  lungs. 

Respiratory  Movements  of  the  Glottis. — Beside  the  movements  of 
respiration  belonging  to  the  chest,  there  are  similar  changes  of  expan- 
sion and  collapse  in  the  larynx.  If  the  respiratory  passages  be  exam- 
ined after  death,  the  opening  of  the  glottis  will  be  found  smaller  in 
calibre  than  the  cavity  of  the  trachea.  The  air-passage  at  the  level 
of  the  glottis  is  a  narrow  chink ;  but  it  widens  considerably  in  the 
lower  part  of  the  larynx,  while  the  trachea  is  a  spacious  cylindrical  tube. 
In  man  the  space  between  the  vocal  chords  has  an  area,  on  the  average, 
of  only  one  square  centimetre ;  while  the  calibre  of  the  trachea  in  the 
middle  of  its  length  is  2.81  square  centimetres.  But  this  disproportion 
does  not  exist  during  life.  In  respiration  there  is  a  regular  movement 
of  the  vocal  chords,  synchronous  with  that  of  the  chest,  by  which  the 
size  of  the  glottis  is  alternately  enlarged  and  diminished.  At  inspira- 


FIG.  55. 


FIG.  56. 


HUMAN  LARYNX,  viewed  from  above  in  its 
ordinary  post-mortem  condition.— a.  Vocal 
chords,  ft.  Thyroid  cartilage,  c,  c.  Aryte- 
noid  cartilages,  o.  Opening  of  the  glottis. 


The  same,  with  the  glottis  opened  by  separa- 
tion of  the  vocal  chords.— a.  Vocal  chords. 
b.  Thyroid  cartilage,  c,  c.  Arytenoid  carti- 
lages, o.  Opening  of  the  glottis. 


tion  the  glottis  opens,  admitting  the  air  freely  into  the  trachea;  at 
expiration  it  collapses,  as  the  air  is  expelled  from  below.  These  move- 
ments are  the  "  respiratory  movements  of  the  glottis."  They  corre- 
spond in  every  respect  with  those  of  the  chest,  and  are  excited  or 
retarded  by  similar  causes.  When  the  general  movements  of  respira- 
tion are  hurried,  those  of  the  glottis  are  also  accelerated ;  and  when 
the  movements  of  the  chest  are  slower  or  fainter  than  usual,  those  of 
the  glottis  are  diminished  in  the  same  proportion. 

In  the  glottis,  as  in  the  chest,  the  movement  of  inspiration  is  an 
active  one,  and  that  of  expiration  passive.  In  inspiration,  the  glottis 
is  opened  by  contraction  of  the  posterior  crico-arytenoid  muscles; 
which  originate  from  the  posterior  surface  of  the  cricoid  cartilage,  and, 
running  thence  upward  and  outward,  are  inserted  into  the  external 
angles  of  the  arytenoid  cartilages.  By  these  muscles,  the  arytnmid 
cartilages  are  rotated  upon  their  articulations,  so  that  the  vocal  chords, 


RESPIRATION.  239 

attached  to  their  anterior  extremities,  are  stretched  and  separated  from 
each  other.  In  this  way,  the  orifice  of  the  glottis  may  be  nearly  doubled, 
its  area  being  increased  from  0.94  to  1.69  square  centimetre. 

At  the  time  of  expiration,  the  posterior  crico-arytenoid  muscles  are 
relaxed,  the  elasticity  of  the  vocal  chords  replacing  them  in  their 
former  position. 

The  mechanism  of  respiration  consists,  therefore,  of  two  sets  of 
movements,  those  of  the  chest  and  those  of  the  glottis.  These  move- 
ments, in  the  normal  condition,  correspond  with  each  other  both  in 
time  and  intensity.  It  is  at  the  same  moment  and  by  the  same 
nervous  influence,  that  the  chest  expands  to  inhale  the  air,  while 
the  glottis  opens  to  admit  it ;  and  in  expiration,  the  muscles  of  both 
chest  and  glottis  are  relaxed,  while  the  elasticity  of  the  tissues  restores 
the  parts  to  their  original  condition. 

Rapidity  of  Respiration. — The  movements  of  respiration  in  man 
follow  each  other  for  the  most  part  with  great  regularity,  and,  according 
to  the  most  extensive  and  varied  observations,  at  the  average  rate  of  20 
inspirations  per  minute.  This  rate  varies  under  different  conditions, 
one  of  the  most  important  of  which  is  age.  As  a  rule,  respiration  is 
more  rapid  in  children  than  in  adults.  Quetelet  has  found  the  average 
rate  in  the  newly  born  infant  44  per  minute,  and  at  the  age  of  5  years 
26  per  minute,  being  reduced  between  the  ages  of  fifteen  and  twenty 
years,  to  the  standard  rapidity  of  20  per  minute.  In  the  adult,  according 
to  the  same  observer,  a  condition  of  rest  or  activity  readily  influences  the 
number  of  respirations  ;  which  are  less  frequent  during  sleep  than  in 
the  waking  condition.  Even  a  difference  in  posture  has  a  perceptible 
effect,  the  number  of  respirations  in  one  individual  being  19  per  minute 
while  lying  down,  and  22  per  minute  when  standing  up.*  Any  special 
muscular  activity,  as  rapid  walking  or  running,  at  once  increases  the 
frequency  of  respiration,  which  returns  to  its  ordinary  regularity  soon 
after  the  exertion  has  ceased. 

The  movements  of  respiration  are  involuntary  in  character,  and  even 
their  acceleration  or  diminution  is  mainly  regulated  by  influences  beyond 
our  control.  It  is  possible  for  a  short  time  to  increase  or  retard  the 
rate  of  respiration,  within  certain  limits,  by  voluntary  effort ;  but  this 
cannot  be  done  continuously.  If  we  intentionally  arrest  the  breathing 
or  diminish  its  frequency,  after  a  short  interval  the  nervous  impulse 
becomes  too  strong  to  be  controlled,  and  the  movements  recommence 
as  usual.  If  on  the  other  hand  we  purposely  accelerate  respiration  to 
any  great  degree,  the  exertion  soon  becomes  too  fatiguing  for  contin- 
uance, and  the  movements  return  to  their  normal  standard. 

Quantity  of  Air  used  in  Respiration. — Like  all  quantitative  esti- 
mates connected  with  respiration,  that  of  the  inspired  and  expired  air 
varies  considerably  as  given  by  different  observers.  The  peculiarities 
)f  individual  constitution,  as  well  as  the  conditions  of  rest  and  activity, 

*  Milne-Edwards,  Lejons  sur  la  Physiologic.    Paris,  1857,  tome  ii.,  p.  483. 


240  FUNCTIONS    OF    NUTRITION. 

prevent  our  arriving  at  an  absolutely  uniform  standard.  The  average 
result,  derived  from  several  of  the  most  trustworthy  experimenters,  as 
well  as  from  our  own  observations,  gives  the  amount  of  air  taken  into 
and  expelled  from  the  lungs  with  each  respiration  as  320  cubic  centi- 
metres. This  estimate  is  certainly  not  above  the  reality.  If  we  take, 
accordingly,  eighteen  respirations  per  minute  as  the  mean  rapidity 
between  the  sleeping  and  waking  hours,  this  would  amount  to  5760 
cubic  centimetres  of  inspired  air  per  minute,  345,600  per  hour,  and 
8,294,400  cubic  centimetres,  or  8294.4  litres  per  day.  But  as  the 
breathing  is  increased,  both  in  rapidity  and  volume,  by  every  muscu- 
lar exertion,  the  daily  quantity  of  air  used  in  respiration  is  not  less 
than  10,000  litres,  or  350  cubic  feet.  This  is  140  times  the  bulk  of 
the  entire  body. 

Estimates  of  this  kind  are  sometimes  used  to  calculate  the  air-space 
necessary  for  each  inmate  of  a  hospital  or  school-room.  This  alone, 
however,  can  never  be  sufficient  for  the  purpose.  The  successful 
ventilation  of  a  room  depends  not  so  much  on  the  quantity  of  air 
which  it  contains  as  on  that  introduced  and  expelled  within  a  certain 
period.  The  air  of  a  small  room,  if  properly  renewed,  may  be  amply 
sufficient  for  respiration,  while  that  of  a  large  room,  if  it  remain  stag- 
nant, will  become  unfit  for  use.  A  large  air-space  will  render  ventila- 
tion more  easy  of  accomplishment  by  ordinary  methods,  because  the 
air  will  not  be  so  rapidly  vitiated  as  if  it  were  in  smaller  volume ;  but 
it  must  still  be  changed  with  a  rapidity  proportionate  to  its  contamina- 
tion, in  order  to  maintain  the  apartment  in  a  wholesome  condition. 


Changes  in  the  Air  by  Respiration. 

The  atmospheric  air  is  a  mixture  of  oxygen  and  nitrogen  in  the  pro- 
portion, by  volume,  of  about  21  parts  of  oxygen  to  19  parts  of  nitro- 
gen. It  also  contains  .05  per  cent,  of  carbonic  acid,  a  varying  quantity 
of  watery  vapor,  and  some  traces  of  ammonia.  The  last  named  ingre- 
dients, so  far  as  animal  respiration  is  concerned,  are  insignificant  in 
comparison  with  the  oxygen  and  nitrogen  which  form  the  principal 
part  of  its  mass. 

As  discharged  from  the  lungs  in  expiration,  the  air  is  found  to 
have  become  altered  in  the  following  particulars :  first,  it  has  lost 
oxygen ;  secondly,  it  has  gained  carbonic  acid  ;  and  thirdly,  it  has 
absorbed  the  vapor  of  water.  The  most  important  of  these  changes 
are  its  diminution  in  oxygen  and  its  increase  in  carbonic  acid. 

Diminution  of  Oxygen. — According  to  Valentin,  Vierordt,  and  Reu-- 
nault  and  Reiset,  the  air  loses  during  respiration,  in  man,  on  an  aver- 
age, five  per  cent,  of  its  volume  of  oxygen.  At  each  inspiration,  about 
16  cubic  centimetres  of  oxygen  are  removed  from  the  air  and  ab- 
sorbed by  the  blood;  and,  as  the  daily  quantity  of  air  used  in  ivspira- 
tion  is  about  10,000  litres,  the  oxygen  consumed  in  twenty-four  hours 
is  not  less  than  500  litres,  or  seven  times  the  bulk  of  the  entire  body. 


RESPIRATION.  241 

This  is,  by  weight,  715  grammes,  or  rather  more  than  one  pound  and 
a  half  avoirdupois. 

The  absorption  of  oxygen  by  different  animals  varies  according  to 
their  functional  activity ;  and  this  difference  exists  even  between  those 
of  the  same  class.  In  the  sparrow  the  amount  of  oxygen  absorbed, 
in  proportion  to  the  bodily  weight,  is  ten  times  as  great  as  in  the 
common  fowl ;  and  in  a  carp  the  quantity  consumed  in  an  hour 
would  hardly  be  sufficient  for  the  respiration  of  a  pigeon  for  a  single 
minute. 

In  the  same  individual  a  temporary  increase  of  muscular  activity 
augments  in  a  marked  degree  the  absorption  of  oxygen.  It  was  found 
by  Lavoiser  and  Seguin  that  a  man,  who  in  the  ordinary  condition 
absorbed  a  little  over  19,000  cubic  centimetres  of  oxygen  per  hour, 
consumed  nearly  13,000  cubic  centimetres  during  fifteen  minutes  of 
active  exercise ;  the  rapidity  of  absorption  being  increased  to  more 
than  2J  times  its  former  rate.  On  the  other  hand,  the  process  is 
diminished  in  activity  during  sleep  ;  and  in  hibernating  animals,  and 
in  insects  undergoing  transformation,  at  the  time  of  their  most  pro- 
found lethargy  it  is  reduced  to  a  mere  vestige,  as  compared  with  their 
usual  condition.  Spallanzani  observed  that  in  insects  the  oxygen  con- 
sumed in  a  given  time  by  the  chrysalis  was  far  less  than  that  absorbed 
by  the  caterpillar  or  the  butterfly;  and  in  the  experiments  of  Reg- 
nault  and  Reiset  on  the  marmot,  the  consumption  of  oxygen  by  this 
animal  at  the  commencement  of  the  cold  season  was  about  500  cubic 
centimetres  per  hour  for  every  kilogramme  of  bodily  weight,  while 
after  hibernation  was  fully  established  it  was  reduced  to  26  cubic  centi- 
metres per  kilogramme  per  hour. 

The  absorption  of  oxygen,  accordingly,  in  respiration,  is  directly 
associated,  in  rapidity  and  amount,  with  the  physiological  activity  of 
the  living  organism. 

Owing  to  its  diminution  in  oxygen,  air  which  has  once  been  breathed 
is  less  capable  of  supporting  respiration  than  before.  When  an  animal 
is  confined  within  a  limited  space,  the  air  becomes  poorer  in  oxygen  as 
respiration  goes  on ;  and  when  its  proportion  has  been  reduced  to  a 
certain  point,  the  animal  dies,  because  a  substance  essential  to  life  is  no 
longer  present  in  sufficient  quantity.  Different  animals  are  affected  in 
various  degrees  by  a  given  diminution  in  the  atmospheric  oxygen. 
Cold-blooded  species,  in  which  respiration  is  comparatively  slow,  may 
still  breathe  when  only  a  very  small  quantity  of  oxygen  is  present ; 
and  it  has  been  found  that  electrical  fishes,  as  well  as  slugs  and  snails, 
may  continue  respiration  until  they  have  completely  exhausted  the 
oxygen  in  the  water  or  air  in  which  they  are  confined.  But  where 
respiration  is  active,  as  in  birds,  quadrupeds,  and  man,  a  partial  reduc- 
tion of  the  oxygen  is  sufficient  to  cause  death.  If  the  carbonic  acid 
exhaled  be  absorbed  by  an  alkaline  solution,  so  that  the  purity  of  the 
air  be  maintained,  it  is  found  that  a  sparrow  dies  in  an  hour  when  the 
proportion  of  oxygen  has  been  reduced  to  15  per  cent. ;  and  a  mouse 

Q 


242  FUNCTIONS    OF    NUTRITION. 

dies  in  five  minutes  when  it  is  reduced  to  10  per  cent.  ;*  the  remainder 
of  the  air  in  both  cases  consisting  of  nitrogen.  In  man  asphyxia  is 
almost  immediately  produced  when  the  proportion  of  oxygen  has  fallen 
to  10  per  cent. 

As  a  candle  flame  is  also  extinguished  in  an  atmosphere  deprived  of 
oxygen,  this  test  is  sometimes  employed  to  determine  whether  it  be 
safe  to  enter  an  atmosphere  of  doubtful  composition.  In  bread-rooms 
and  beer-vats,  where  fermentation  has  been  going  on,  in  wells  which 
have  been  for  a  long  time  closed,  or  in  old  underground  cavities  or 
passages,  the  atmosphere  is  frequently  so  poor  in  oxygen  that  it  would 
be  unsafe  to  enter  them  without  precaution.  A  lighted  candle  is, 
accordingly,  let  down  into  the  suspected  cavity,  and  if  sufficient  oxygen 
be  present,  it  continues  to  burn ;  if  not,  it  is  extinguished. 

This  test  is  the  more  valuable,  because  the  proportion  of  oxygen 
necessary  for  the  combustion  of  a  candle  is  greater  than  that  required 
for  the  immediate  support  of  respiration.  A  candle  is  extinguished 
when  the  air  contains  only  17  per  cent,  of  its  volume  of  oxygen,  while 
less  than  this  may  still  serve  a  short  time  for  respiration.  According 
to  Milne-Edwards,  a  man  may  respire  in  an  atmosphere  which  is  in- 
sufficient to  support  combustion ;  and  we  have  repeatedly  seen  pigeons 
continue  to  breathe  in  air  in  which  a  candle  flame  was  immediately 
extinguished. 

But  although  an  atmosphere  containing  from  10  to  IT  per  cent,  of 
oxygen  is  not  at  once  fatal  to  man,  it  is  still  unfit  for  continued  breath- 
ing, and  after  a  time  its  deleterious  effects  would  become  manifest.  A 
complete  renewal  of  the  deteriorated  air,  in  such  cases,  is  essential  to 
the  perfect  performance  of  respiration. 

Increase  of  Carbonic  Acid. — The  expired  air  usually  contains,  in 
man,  about  4  per  cent,  of  its  volume  of  carbonic  acid,  which  it  has  ab- 
sorbed in  the  lungs.  Rather  less  than  13  cubic  centimetres  of  this  gas 
are,  therefore,  given  off  with  each  ordinary  expiration ;  and  as  10,000 
litres  of  air  are  inhaled  and  discharged  during  twenty-four  hours,  this 
will  give  400  litres  of  carbonic  acid  as  the  amount  expired  per  day. 
This  quantity  is,  by  weight,  786  grammes,  or  rather  less  than  one 
pound  and  three-quarters  avoirdupois. 

The  exhalation  of  carbonic  acid  by  respiration  varies,  for  the  most 
part,  in  a  similar  way,  with  the  absorption  of  oxygen.  In  general,  it 
may  be  said,  as  the  result  of  many  trustworthy  observations,  both  in 
animals  and  man,  that  the  carbonic  acid  exhaled  during  a  given  time, 
is  increased  by  muscular  exertion,  or  any  other  physiological  activity 
of  the  system,  and  is  diminished  by  quietude,  during  sleep,  and  in  a 
state  of  inanition. 

These  facts  were  first  established,  particularly  for  the  human  subject, 
by  Scharling,f  who  found  that  the  quantity  of  carbonic  acid  exhaled 

*  Milne-Edwards,  Lefons  sur  la  Physiologic.     Paris,  1857,  tome  ii.,  p.  638. 
f  Annales  de  Chimie  et  de  Physique.     Paris,  1843,  tome  viii.,  p.  490. 


RESPIRATION.  243 

was  greater  during  digestion  than  in  the  fasting  condition;  in  the 
waking  hours  than  during  sleep ;  and  in  a  state  of  activity  than  in 
one  of  repose.  It  was  diminished  by  fatigue,  and  by  most  conditions 
which  interfere  with  health. 

In  man  the  rate  of  exhalation  also  varies  according  to  age,  sex,  con- 
stitution, and  development.  These  variations  were  investigated  by 
Andral  and  Gavarret,  who  found  them  very  marked  in  different  indi- 
viduals, notwithstanding  that  the  experiments  were  made  at  the  same 
period  of  the  day,  and  with  the  subject  as  nearly  as  possible  in  the 
same  condition.  The  carbonic  acid  exhaled  per  hour  in  five  different 
persons  was  as  follows  : 

QUANTITY  OF  CARBONIC  ACID  PER  HOUR. 

In  subject  Ko.  1 19,770  cubic  centimetres. 

"2 15,888     "  " 

"        "        "  3 20,475     "  " 

u        "        "  4  .         .        .        .        .  20,475     "  " 

"         "         u  5 26,060     "  " 

From  eight  years  up  to  puberty  the  quantity  of  carbonic  acid  in- 
creases constantly  with  the  age.  Thus  a  boy  of  eight  years  exhales, 
on  the  average,9238  cubic  centimetres  per  hour;  while  a  boy  of  fifteen 
exhales  16,168  cubic  centimetres  in  the  same  time.  Boys  exhale  during 
this  period  more  carbonic  acid  than  girls  of  the  same  age.  In  males 
the  quantity  of  carbonic  acid  increases  until  the  twenty-fifth  or  thir- 
tieth year,  when  it  reaches,  on  the  average,  22,899  cubic  centimetres 
per  hour.  It  then  remains  stationary  for  ten  or  fifteen  years ;  dimin- 
ishes slightly  from  the  fortieth  to  the.  sixtieth  year ;  and  after  sixty 
shows  a  marked  reduction,  falling  sometimes  as  low  as  17,000  cubic 
centimetres.  In  one  superannuated  person,  102  years  of  age,  the  hourly 
quantity  was  less  than  11,000  cubic  centimetres. 

In  women,  the  increase  of  carbonic  acid  ceases  at  puberty ;  its  pro- 
duction then  remaining  constant  until  the  cessation  of  menstruation, 
about  the  fortieth  or  forty-fifth  year.  At  that  time  it  increases  again 
until  after  fifty  years,  when  it  subsequently  diminishes  with  the 
approach  of  old  age,  as  in  men.  Pregnancy,  occurring  at  any  time 
in  the  above  period,  produces  a  temporary  increase  in  the  quantity  of 
carbonic  acid. 

The  strength  of  constitution,  and  particularly  the  development  of 
the  muscular  system,  has  great  influence  in  this  respect.  The  largest 
production  of  carbonic  acid  observed  was  in  a  young  man,  26  years  of 
age,  of  remarkably  vigorous  and  athletic  development,  who  exhaled 
26,060  cubic  centimetres  per  hour.  On  the  other  hand,  an  unusually 
large  skeleton,  or  an  abundance  of  adipose  tissue,  is  not  accompanied 
by  a  corresponding  increase  in  carbonic  acid. 

The  discharge  of  carbonic  acid  is  not  altogether  confined  to  the 
lungs,  but  takes  place  also,  in  some  measure,  by  the  urine  and  the  per- 


244  FUNCTIONS    OP    NUTRITION. 

spiration.  Morin*  found  that  the  urine  always  contains  in  solution 
certain  gases,  of  which  carbonic  acid  is  the  most  abundant.  The  mean 
result  of  fifteen  observations  showed  that  urine  excreted  during  the 
night  contains  about  1.96  per  cent,  of  its  volume  of  carbonic  acid.  During 
the  day  the  quantity  of  this  gas  varies  considerably,  according  to  the 
condition  of  repose  or  activity ;  since  after  remaining  quiet  for  an  hour 
or  two,  it  was  only  1.19  per  cent,  of  the  volume  of  the  urine,  while 
after  continued  exertion  for  a  similar  period  the  urine  was  augmented 
in  quantity,  and  its  proportion  of  carbonic  acid  at  the  same  time  nearly 
doubled,  amounting  to  2.29  per  cent,  of  its  volume. 

An  equal  or  even  greater  activity  of  gaseous  exhalation  takes  place 
by  the  skin.  It  has  been  found,  by  inclosing  one  of  the  limbs  in  an 
air-tight  case,  that  the  air  in  which  it  is  confined  loses  oxygen  and  gains 
carbonic  acid.  From  an  experiment  of  this  sort,  Scharling  estimated 
the  carbonic  acid  given  off  from  the  whole  cutaneous  surface,  in  man, 
as  from  one-sixtieth  to  one-thirtieth  of  that  discharged  by  the  lungs. 
In  the  more  recent  observations  of  Aubert,  the  whole  body  without 
clothing,  was  confined  in  an  air-tight  case,  leaving  only  the  head 
exposed.  Ventilation  was  kept  up  during  the  experiment  with  air 
free  from  carbonic  acid,  while  the  carbonic  acid  exhaled  from  the 
body  was  absorbed  by  baryta-water.  Each  observation  lasted  for  two 
hours,  and  the  average  result  obtained  was  that,  for  the  entire  day 
of  twenty-four  hours,  198  cubic  centimetres  of  carbonic  acid  wore 
exhaled  from  the  skin  ;  a  quantity  representing  rather  less  than  one 
two-hundredth  of  that  given  off  by  the  lungs. 

In  the  amphibious  reptiles,  as  frogs,  newts,  and  salamanders,  which 
breathe  by  lungs,  and  yet  can  remain  under  water  for  a  considerable 
time,  the  integument  takes  a  more  active  part  in  respiration.  The 
skin  of  these  animals,  which  is  thin,  moist,  and  covered  with  a  deli- 
cate epithelial  layer,  presents  the  most  favorable  conditions  for  gaseous 
transudation ;  and  beneath  the  surface  of  the  water,  while  the  lungs 
are  comparatively  inactive,  exhalation  and  absorption  take  place  through 
the  skin,  and  respiration  goes  on  almost  without  interruption. 

Indifference  of  Nitrogen  in  the  Act  of  Respiration.  —  Notwith- 
standing the  abundance  of  free  nitrogen  in  the  atmosphere,  and  its 
existence  to  some  extent  in  the  circulating  fluids,  this  substance  takes 
no  direct  part  in  respiration  or  nutrition.  Even  in  vegetables,  the 
nitrogen  required  for  their  albuminous  ingredients  is  derived  only  from 
pre-existing  nitrogenous  compounds,  mainly  nitrates  and  ammonium 
salts.  In  animals,  according  to  the  conclusions  generally  accepted, f 
there  is  no  satisfactory  evidence  that  the  free  nitrogen  of  the  air  hits 
any  share  in  the  phenomena  of  combination  or  decomposition  within 
the  body.  It  appears  to  serve  as  a  vehicle  or  medium  of  admixture 
fur  the  introduction  of  oxygen;  remaining  in  other  respects  an  indif- 
ferent substance  in  the  respiratory  process. 

*  Journal  de  Pharmacie  et  de  Chimie.     Paris,  1864,  tome  xlv.,  p.  396. 
f  Hoppe-Seyler,  Physiologische  Cheraie.     Berlin,  1877,  p.  48. 


RESPIRATION.  245 

Discharge  of  Water  in  Eespiration. — The  water  exhaled  with  the 
breath  is  given  off  by  the  pulmonary  mucous  membrane,  by  which  it 
is  absorbed  from  the  blood.  At  ordinary  temperatures  it  is  a  transpa- 
rent, invisible  vapor ;  but  in  cold  weather  it  becomes  partly  condensed 
on  leaving  the  lungs,  and  appears  as  a  cloudy  precipitate  in  the  breath. 
According  to  Valentin,  the  average  quantity  exhaled  from  the  lungs  is 
about  500  grammes  per  day. 

The  exhalation  of  water  by  the  lungs  is  a  physical  process, 
dependent  on  the  moist  and  permeable  structure  of  the  pulmonary 
membrane  and  the  vaporization  of  watery  fluid  at  the  ordinary  press- 
ure of  the  atmosphere.  Any  moist  animal  membrane,  after  death  as 
well  as  during  life,  loses  water  by  evaporation  and  becomes  gradually 
desiccated.  Experiments  on  recently  killed  frogs  show  that  sponta- 
neous desiccation  goes  on  at  first  rapidly,  and  afterward  more  slowly, 
as  the  proportion  of  water  in  the  tissues  is  diminished.  In  the  lungs 
of  a  warm-blooded  animal  during  life  all  the  requisite  conditions  for 
rapid  evaporation  are  present,  namely,  a  moderately  elevated  tempera- 
ture, a  constant  renewal  of  atmospheric  air  by  the  movements  of 
respiration,  and  a  continuous  supply  of  moisture  by  the  circulating 
blood.  The  watery  vapor  exhaled  is  therefore  increased  or  diminished 
according  to  the  rapidity  of  respiration,  dryness  or  humidity  of  the 
atmosphere,  and  the  activity  of  the  pulmonary  circulation. 

In  some  animals,  as  in  the  dog,  where  the  integument  is  compara- 
tively deficient  in  perspiratory  glands,  the  pulmonary  transpiration 
becomes  more  active ;  and  it  is  not  uncommon  for  these  animals,  in 
hot  weather,  to  lie  at  rest  with,  their  tongues  protruded,  and  breathing 
from  one  hundred  to  two  hundred  times  per  minute,  for  the  purpose 
of  increasing  the  watery  exhalation  from  the  lungs. 

In  man  the  precise  physiological  value  of  the  pulmonary  transpira- 
tion is  not  known.  Though  varying  according  to  the  physical  condi- 
tions above  mentioned,  it  is  a  continuous  process,  and  even  at  ordinary 
temperatures  the  expired  breath  received  on  a  polished  glass  or  metallic 
surface  will  produce  an  immediate  dimness  by  the  condensation  of 
moisture.  It  is  possible  that  the  vapor  thus  exhaled,  beside  being 
complementary  to  the  cutaneous  perspiration,  may  also  serve  as  a 
vehicle  for  the  discharge  of  other  substances. 

Exhalation  of  Organic  Matter  by  the  Breath. — Beside  carbonic  acid 
and  water,  the  expired  air  contains  an  organic  ingredient,  which  com- 
municates a  faint  but  perceptible  odor  to  the  breath.  This  substance 
is  discharged  as  an  ingredient  in  the  watery  vapor  of  respiration. 
Under  ordinary  circumstances  it  is  in  so  small  quantity  as  to  be  hardly 
noticeable ;  but  if  a  large  number  of  persons  remain  for  some  hours  in 
an  apartment  with  insufficient  ventilation,  it  accumulates  in  the  atmos- 
phere to  such  an  extent  that  its  odor  becomes  offensive.  According  to 
Carpenter,  the  watery  fluid  condensed  from  the  expired  air,  if  kept  in 
a  closed  vessel  at  ordinary  temperatures,  exhales,  after  a  time,  a  putres- 
cent  odor  which  could  only  come  from  decomposing  organic  substances. 


246  FUNCTIONS    OF    NUTRITION, 

When  fresh  and  in  the  healthy  condition,  the  organic  ingredient  of 
the  expired  breath  is  not  offensive  and  appears  to  have  no  unwhole- 
some qualities.  It  is  only  when  accumulated  in  undue  quantity,  and 
allowed  to  stagnate  in  the  atmosphere,  that  its  disagreeable  properties 
become  manifest.  It  appears  to  be  distinct  in  character  for  each  species 
of  animal ;  and  as  it  is  liable  to  be  absorbed  and  retained  by  porous 
materials,  such  as  wood,  plaster,  or  woven  fabrics,  its  odor  remains 
perceptible  in  any  small  inclosure  or  transportation-car  in  which  such 
animals  have  been  confined.  It  has  not  been  isolated  in  any  case  in 
sufficient  quantity  to  determine  its  exact  composition. 

Vitiation  of  Air  by  Continued  Respiration. — It  appears  from  the 
foregoing  that  the  air,  when  discharged  in  expiration,  has  been  deteri- 
orated by  the  loss  of  oxygen,  and  by  the  addition  of  matters  derived 
from  the  lungs.  Under  ordinary  conditions,  the  deteriorated  air  is  at 
once  diffused  in  the  surrounding  atmosphere,  rising  to  a  higher  level 
on  account  of  its  increased  temperature,  and  dispersed  by  the  aerial 
currents ;  so  that  a  fresh  supply,  of  normal  constitution,  is  taken  into 
the  lungs  with  each  inspiration.  But  when  breathing  is  carried  on  in 
a  limited  space,  the  air  necessarily  becomes  vitiated ;  and  this  effect  is 
produced  with  greater  rapidity,  the  smaller  the  volume  of  the  air  and 
the  larger  the  number  of  men  or  animals  using  it  for  respiration. 

The  vitiation  of  the  air  by  respiration  is,  accordingly,  the  result  of 
several  changes  taking  place  at  the  same  time,  and  its  effects  are  due 
to  all  these  alterations  combined. 

So  far  as  regards  immediate  danger  to  life,  the  diminution  of  oxygen 
is  the  most  important  change  in  the  vitiated  air,  when  carried  to  a 
sufficient  extent.  We  have  already  seen  that  for  man  and  mammalians, 
the  air  is  completely  irrespirable  when  its  proportion  of  oxygen  is 
diminished  to  10  per  cent.  In  these  experiments,  however,  the  exhaled 
carbonic  acid  was  removed,  as  fast  as  produced,  by  the  action  of  an 
alkaline  solution,  so  that  the  air  remained  in  a  state  of  purity  except 
for  its  loss  of  oxygen.  But  if  the  products  of  respiration  be  allowed 
to  accumulate  at  the  same  time,  the  loss  of  oxygen  is  more  quickly  felt. 
In  the  experiments  of  Leblanc,  a  dog  and  a  pigeon,  breathing  in  a  con- 
fined space,  were  both  reduced  to  extremities  when  the  air  was  con- 
taminated with  30  per  cent,  of  carbonic  acid,  though  still  containing 
16  per  cent,  of  oxygen. 

The  second  element  in  the  vitiation  of  the  respired  air  is  the  presence 
of  carbonic  acid.  The  effect  of  this  gas,  as  produced  by  respiration, 
cannot  be  ascertained  from  that  of  carbonic  acid  alone.  A  man  or  an 
animal,  suddenly  introduced  into  an  atmosphere  of  pure  carbonic  acid, 
dies  at  once  by  suffocation.  But  this  result  is  not  caused  by  tin-  in- 
fluence of  carbonic  acid.  It  is  due  to  the  absence  of  oxygen  ;  and 
death  would  take  place  as  promptly  in  an  atmosphere  of  nitrogen  or 
any  other  indifferent  gas.  It  may  be  said  that,  in  general,  for  birds 
and  small  mammalians,  the  atmosphere  becomes  incapable  of  sup- 
porting life  when,  in  addition  to  its  normal  proportion  of  oxygen,  it 


RESPIRATION.  247 

contains  20  per  cent,  of  carbonic  acid ;  that  is,  five  times  as  much  as 
is  present,  in  man,  in  the  expired  breath.  But  Regnault  and  Reiset 
found  that  dogs  and  rabbits  could  continue  to  breathe  without  diffi- 
culty in  an  atmosphere  containing  even  23  per  cent,  of  carbonic  acid, 
provided  its  oxygen  were  increased  to  30  or  40  per  cent.  Thus  a  part, 
at  least,  of  the  influence  of  carbonic  acid,  when  in  large  quantity,  is  due  to 
its  action  in  excluding  or  interfering  with  the  absorption  of  oxygen. 

Pure  carbonic  acid,  mixed  with  atmospheric  air  of  normal  constitu- 
tion, is  not  so  fatal  in  its  effect  as  sometimes  represented.  If  a  pigeon 
be  confined  in  a  glass  receiver  with  a  wide  open  mouth,  and  carbonic 
acid  be  introduced  through  a  tube  placed  just  within  the  edge  of  the 
vessel,  so  that  it  will  gradually  mingle  with  the  air,  it  produces  rapid 
and  laborious  respiration,  gradually  increasing  in  intensity ;  and  in  a 
few  moments  the  animal  falls  in  a  state  of  insensibility.  But  if  the 
receiver  be  removed,  allowing  the  free  access  of  fresh  air,  the  insen- 
sibility soon  passes  off,  and  in  a  few  moments  the  animal  is  again 
breathing  in  a  natural  manner,  without  having  suffered  any  permanent 
injury.  The  action  of  carbonic  acid,  administered  in  this  way,  is 
similar  to  that  of  an  anaesthetic  vapor,  like  ether  or  chloroform,  with 
the  addition  of  strong  symptoms  of  dyspnoea. 

In  man  the  immediate  effects  of  carbonic  acid  in  the  inspired  air  are 
of  a  similar  nature.  The  inhalation  of  pure  carbonic  acid  from  a  gas- 
ometer is  at  first  extremely  difficult,  as  its  stimulating  effect  on  the 
mucous  membrane  produces  spasmodic  stricture  of  the  glottis.  If 
the  gas,  however,  be  allowed  to  remain  for  a  short  time  in  contact 
with  the  mucous  membrane  this  effect  passes  off,  the  glottis  may  be 
gently  opened,  and  the  carbonic  acid  drawn  into  the  lungs,  by  a  deep 
inspiration,  to  the  amount  of  from  800  to  1200  cubic  centimetres.  At 
first  it  produces  only  a  sensation  of  warmth  and  moderate  stimulus  in 
the  chest.  But  at  the  end  of  two  or  three  seconds  there  comes  on  very 
suddenly  a  sense  of  extreme  dyspnoea,  with  rapid  and  laborious  respi- 
ration, followed  by  dimness  of  vision,  slight  confusion  of  mind,  and 
partial  insensibility,  all  of  which  symptoms  soon  disappear,  as  respira- 
tion returns  to  its  normal  condition,  leaving  a  feeling  of  quietude  and 
tendency  to  sleep. 

Notwithstanding,  however,  the  intense  feeling  of  dyspnea  produced 
by  such  an  inhalation,  the  external  signs  of  suffocation  are  very  slight, 
and  bear  no  proportion  to  the  severity  of  the  sensations.  They  are 
confined  to  a  little  suffusion  of  the  face,  with  partial  lividity  of  the 
lips ;  and  the  pulse  is  but  little  if  at  all  affected. 

A  mixture  of  carbonic  acid  and  atmospheric  air  in  equal  volumes  pro- 
duces a  perceptible  feeling  of  warmth  and  pungency  at  the  glottis,  but 
may  still  be  readily  drawn  into  the  lungs.  After  two  or  three  deep 
inspirations,  the  strong  sense  of  want  of  air,  with  rapid  and  laborious 
respiration,  comes  on  as  before.  The  dyspnoea,  suffusion  of  face,  and 
lividity  are  less  marked  than  after  breathing  the  pure  gas,  but  the 
subsequent  condition  of  quiescence  and  partial  anaesthesia,  is  more 
decided  and  of  longer  continuance. 


248  FUNCTIONS    OF    NUTRITION. 

A  mixture  of  one  volume  of  carbonic  acid  with  three  volumes  of 
atmospheric  air  may  be  inspired  without  difficulty,  producing  a  rather 
agreeable  sensation  in  the  lungs.  After  about  3000  cubic  centimetres 
have  been  inhaled  in  successive  inspirations,  a  sense  of  dyspnoea  comes 
on,  which,  however,  is  not  particularly  increased  by  continuing  the 
inspiration  to  6000  cubic  centimetres.  The  nervous  symptoms  are 
moderate  in  degree,  but  similar  to  the  preceding. 

On  the  other  hand,  pure  nitrogen  has  no  taste  nor  odor,  nor  does  it 
have  any  stimulating  effect  on  the  mucous  membrane.  It  may  be  in- 
spired to  the  amount  of  GOOO  cubic  centimetres,  without  producing  any 
sense  of  dyspnoea,  or  any  perceptible  effect  on  the  nervous  system. 

These  results  indicate  that  the  presence  of  carbonic  acid  in  the  lungs 
acts  as  a  stimulus  to  respiration  by  causing  a  sense  of  the  want  of  air ; 
and  that,  furthermore,  its  principal  toxic  effect,  when  in  abnormal  quan- 
tity, is  the  production  of  more  or  less  insensibility  or  anaesthesia.  The 
sense  of  drowsiness  and  inattention  experienced  in  an  imperfectly  ven- 
tilated lecture-room  or  theatre  is  probably  due  to  this  cause,  especially  as 
the  burning  gas-lights  contribute  at  the  same  time  to  the  formation  of  car- 
bonic acid.  The  temporary  nature  of  these  sensations,  and  their  immedi- 
ate relief  on  coming  into  the  open  air,  are  matters  of  common  observation. 

The  third  element  in  the  vitiation  of  air  by  the  breath  is  the  exhala- 
tion of  organic  vapor.  This  is  the  least  understood,  but  probably  the 
most  deleterious  ingredient  of  the  atmosphere  produced  by  respiration. 
It  is  this  which  causes  the  offensive  odor,  and  the  sense  of  oppression 
on  entering  any  confined  space,  where  too  great  a  number  of  persons 
have  remained  without  sufficient  renewal  of  the  air.  It  is  most  marked 
when  continued  respiration,  with  neglect  of  ventilation,  has  been  going 
on  over  night,  as  in  a  crowded  dormitory  or  sleeping-car  ;  since  the 
organic  emanations  have  then  had  time  not  only  to  accumulate  but 
also  to  pass  into  a  state  of  incipient  decomposition.  In  this  condition 
they  resemble  the  class  of  animal  poisons ;  and  there  is  reason  to 
believe,  that  when  introduced  into  the  system,  they  may  cause  dis- 
turbances which  last  for  a  considerable  time.  It  is  certain  that  the 
contagion  of  many  febrile  diseases  is  communicated  through  the  air  by 
the  products  of  respiration ;  and  the  normal  organic  exhalations  of  the 
pulmonary  mucous  membrane,  when  altered  by  concentration,  the  accu- 
mulation of  moisture,  and  an  elevated  temperature  are  perhaps  capable 
of  producing  analogous  effects. 

All  the  above  causes  of  vitiation  of  the  atmosphere  in  respiration, 
notwithstanding  the  differences  in  their  nature  and  effects,  are  to  be 
obviated  by  the  same  means;  that  is,  a  sufficient  renewal  of  the  air  by 
ventilation. 

Relation  between  the  Oxygen  absorbed  in  Respiration  and  the  Carbonic 
Acid  given  off. — It  has  been  seen  that,  in  man,  with  each  respiration,  on 
the  average,  1C  cubic  centimetres  of  oxygen  are  absorbed,  and  13  cubic  cen- 
timetres of  carbonic  acid  given  off.  As  the  oxygen  thus  taken  in  weighs 
rather  less  than  .023  gramme  while  the  carbonic  acid  discharged  weighs 


RESPIRATION.  249 

.025  gramme,  it  is  evident  that  the  gross  result  is  a  loss  of  weight  to 
the  system,  and  this  loss,  by  continued  respiration,  amounts  on  the 
average  to  a  little  over  70  grammes  per  day.  This  is  one  of  the  most 
important  facts  connected  with  respiration.  It  shows  that  this  function 
is  carried  on  at  the  expense  of  the  bodily  substance,  since  the  oxygen 
and  carbon  discharged  under  the  form  of  carbonic  acid  weigh  more 
than  the  oxygen  absorbed  in  a  free  state.  The  difference  must  accord- 
ingly be  supplied  in  some  way  by  the  food ;  and  if  this  be  withheld, 
respiration  alone  will  be  sufficient  to  diminish  gradually  the  weight  of 
the  body,  and  to  bring  it  at  last  to  a  state  of  emaciation. 

If  we  endeavor  to  ascertain  what  becomes  of  the  inspired  oxygen, 
it  appears,  in  the  first  place,  that  the  quantity  of  this  gas  which  disap- 
pears from  the  air  is  not  entirely  replaced  in  the  carbonic  acid  of  the 
breath  ;  that  is,  there  is  less  oxygen  in  the  carbonic  acid  returned  to 
the  air  by  expiration  than  has  been  taken  from  it  by  inspiration. 

The  proportion  of  oxygen  which  disappears  in  the  body,  over  and 
above  that  returned  by  the  breath  as  carbonic  acid,  varies  in  different 
animals.  In  the  herbivora  it  is  about  10  per  cent,  of  the  oxygen 
inspired ;  in  the  carnivora,  20  or  25  per  cent. ;  and  even  in  the  same 
animal,  the  proportion  of  oxygen  absorbed,  to  that  of  carbonic  acid 
exhaled,  varies  according  to  the  food  upon  which  he  subsists.  In 
dogs  fed  on  meat,  according  to  Regnault  and  Reiset,*  25  per  cent, 
of  the  inspired  oxygen  disappears  in  the  body  of  the  animal ;  but  when 
fed  on  starchy  substances,  all  but  8  per  cent,  reappears  in  the  expired 
carbonic  acid.  Under  some  conditions,  there  may  be  a  difference  in 
the  opposite  direction ;  that  is,  more  oxygen  may  be  contained  in  the 
carbonic  acid  exhaled  than  is  absorbed  in  a  free  state  from  the  atmos- 
phere. In  some  of  the  experiments  of  Regnault  and  Reiset,  with 
rabbits  and  fowls  fed  exclusively  on  bread  and  grain,  the  oxygen  in 
the  expired  carbonic  acid  was  101  or  102  per  cent,  of  that  taken  in  by 
respiration;  and  even  in  man,  according  to  Doyere,  the  quantity  of 
oxygen  discharged  as  carbonic  acid,  may  be  considerably  greater  than 
that  absorbed.  But  in  general  it  is  the  reverse;  the  quantity  of 
oxygen  not  accounted  for  in  the  expired  carbonic  acid  being  habitually 
greater  in  the  carnivorous  animals  than  in  the  herbivora. 

These  facts  have  been  established  by  direct  observation,  without 
reference  to  the  supposed  manner  in  which  the  internal  changes  of 
respiration  take  place.  Nevertheless,  they  are  susceptible  of  so  ready 
an  explanation  that  there  can  be  little  doubt  of  their  significance.  The 
simplest  case  would  be  that  of  an  herbivorous  animal  living  exclusively 
on  carbo-hydrates,  as  starch  or  sugar.  Since  these  substances  already 
contain  oxygen  and  hydrogen  in  the  proportions  to  form  water,  any 
further  oxidation  must  result  in  the  production  of  carbonic  acid ;  and 
in  this  case  the  same  quantity  of  oxygen  as  that  taken  in  must  be 
returned  to  the  atmosphere  as  a  constituent  of  the  carbonic  acid 
exhaled :  the  remainder  of  the  carbo-hydrate  being  separated  in  the 
form  of  water.  This  process  is  represented  in  the  following  fornrula_^ 
*Annales  de  Chimie  et  de  Physique.  Paris,  1849,  tome  xxvi.,  pp.  409-451. 


250  FUNCTIONS    OF    NUTRITION. 

Starch.  Carbonic  acid.    Water. 

06H1006  +  019  =  0(C02)  +  5(11,0). 

In  an  animal  supported  on  this  food,  the  whole  of  the  oxygen  taken 
in  by  respiration  would  reappear  in  the  expired  carbonic  acid.  But 
in  an  animal  also  consuming  fatty  substances,  the  proportions  would 
be  changed.  As  these  matters  do  not  contain  enough  oxygen  to  form 
water  with  their  hydrogen,  more  oxygen  must  be  taken  in  with  the 
breath  than  is  needed  to  convert  their  carbon  into  carbonic  acid  ;  and  a 
part  of  it  will  consequently  disappear  from  the  gaseous  products  of 
respiration.  The  change  in  this  instance  is  as  follows : 

Oleine.  Carbonic  acid.         Water. 

067H10406  +  0160  =  57(C02)  +  62(H,0). 

In  effecting,  therefore,  the  complete  disappearance  of  a  fatty  sub- 
stance, 160  parts  of  oxygen  will  be  absorbed,  and  only  114  parts 
returned  in  the  carbonic  acid.  This  will  also  take  place  where  albu- 
minous matters  are  used  as  food,  since  all  the  nitrogen  of  these  sub- 
stances is  excreted  in  the  form  of  urea ;  and  after  the  separation  of 
urea  from  albumen,  what  is  left  must  be  analogous  in  composition  to 
fat ;  that  is,  containing  less  oxygen  than  would  be  required  to  convert 
its  hydrogen  into  water. 

It  is  no  doubt  for  these  reasons  that,  in  herbivorous  animals,  feeding 
largely  on  carbo-hydrates,  the  oxygen  exhaled  in  the  carbonic  acid  is 
nearly  equal  to  that  taken  in  with  the  breath;  while  in  carnivora, 
which  consume  only  fats  and  albuminous  matters,  a  larger  proportion 
of  oxygen  disappears  from  the  products  of  respiration. 

Finally,  some  kinds  of  vegetable  food,  as  fruits  and  green  tissues, 
contain  substances,  the  oxygen  of  which  is  more  than  sufficient  to  form 
water  with  their  hydrogen.  Such  are  the  salts  of  vegetable  acids,  like 
oxalic,  citric,  gallic,  malic,  and  tartaric  acid.  The  result  of  the  internal 
consumption  of  tartaric  acid,  for  example,  would  be  as  follows : 

Tartaric  acid.          Carbonic  acid.     Water. 
C4H60,  +  06  =  4(OOJ  +  8(H,0). 

In  this  instance  more  oxygen  will  be  exhaled,  in  the  carbonic  acid 
produced,  than  was  absorbed  from  the  atmosphere ;  because  a  super- 
abundance already  existed  in  the  material  used  as  food. 

The  proportions  of  oxygen  and  carbonic  acid,  absorbed  and  expired 
in  respiration,  will  therefore  vary,  as  shown  by  Mayer,*  not  only  with 
the  nature  of  the  food,  but  also  according  to  the  transformations,  within 
the  living  organism,  of  one  nutritive  substance  into  another,  as  of  a 
carbohydrate  into  a  fat,  or  of  either  into  an  organic  acid.  In  the  fer- 
mentation of  glucose  (p.  57)  there  is  even  an  elimination  of  carbonic 
acid  without  any  absorption  of  oxygen  whatever;  this  being  a  process, 
not  of  direct  oxidation,  but  of  the  rearrangement  of  elements  already 
present  in  the  sugar,  a  portion  bein.ir  exhaled  as  carbonic  acid,  while 
the  rest  remain  in  the  form  of  alcohol. 

*Lehrbuch  der  Agrikultur-Chemie.     IK-uk-lberg,  1871,  p.  101. 


RESPIRATION.  251 

Changes  in  the  Blood  by  Respiration. 

The  blood  as  it  circulates  in  the  arterial  system  has  a  bright  scarlet 
color;  but  in  passing  through  the  capillaries  it  gradually  becomes 
darker,  and  on  arriving  in  the  veins  it  is  deep  purple,  or  in  some  situ- 
ations nearly  black.  There  are,  therefore,  two  kinds  of  blood  in  the 
body  ;  arterial  blood,  which  is  of  a  bright  color,  and  venous  blood, 
which  is  dark.  The  dark  colored  venous  blood  is  incapable,  in  this 
state,  of  supplying  the  organs  with  their  normal  stimulus  and  nutri- 
tion, and  has  thus  far  lost  its  value  as  a  circulating  fluid.  It  is  accord- 
ingly returned  to  the  heart  by  the  veins,  and  is  thence  sent,  through 
the  pulmonary  artery,  to  the  lungs.  In  passing  through  the  pulmo- 
nary circulation  it  reassumes  its  scarlet  hue,  and  is  again  converted  into 
arterial  blood.  Thus  the  most  striking  physical  effect  produced  in  the 
blood  by  respiration  is  its  change  of  color  from  venous  to  arterial. 

This  change  is  effected  by  the  air  in  the  pulmonary  cavities.  If  defi- 
brinated  blood,  recently  drawn  from  the  veins,  be  shaken  up  with  atmos- 
pheric air,  it  at  once  changes  its  color  and  acquires  the  bright  hue  of 
arterial  blood.  If  forced  by  injection  through  the  blood-vessels  of 
the  inflated  lungs,  it  exhibits  the  same  change.  In  a  dog,  or  other 
mammalian,  if  the  thorax  be  opened,  and  artificial  respiration  kept  up 
by  the  nozzle  of  a  bellows  inserted  into  the  trachea,  the  dark  venous 
blood  can  be  seen  in  the  great  veins  and  in  the  right  auricle  of  the 
heart,  while  that  returning  from  the  lungs  to  the  left  auricle  is  bright 
red.  If  respiration  be  suspended,  the  blood  soon  ceases  to  be  arterial- 
ized  in  the  lungs,  and  returns  to  the  left  auricle  of  a  dark  venous  hue.  On 
recommencing  respiration,  the  blood  is  again  arterialized,  its  red  color 
reappearing  in  the  pulmonary  veins  and  the  left  cavities  of  the  heart. 

Simultaneously  with  its  alteration  of  color  during  the  pulmonary 
circulation,  the  blood  undergoes  a  change  in  its  gaseous  constituents, 
the  converse  of  that  which  is  produced  in  the  air ;  that  is,  it  absorbs 
oxygen  and  exhales  carbonic  acid. 

Passage  of  Oxygen  into  the  Blood  in  Respiration. — The  oxygen 
which  disappears  from  the  air  in  the  lungs  is  taken  up  by  the  blood 
in  the  pulmonary  capillaries.  It  does  not  enter  into  immediate  chem- 
ical union  with  the  organic  ingredients  present,  but  remains  in  such 
loose  combination  that  it  may  be  removed  from  the  blood  by  the 
air-pump,  or  by  a  current  of  hydrogen  or  nitrogen,  and  especially  by 
the  action  of  carbonic  oxide  (C  0),  which  expels  it  completely.  Ac- 
cording to  a  large  number  of  observations,  its  quantity,  in  the  arterial 
blood  of  the  dog,  may  vary  from  a  little  over  10  per  cent,  to  22  per 
cent,  by  volume ;  the  average,  in  the  experiments  of  Schoeffer  and 
Ludwig,*  being  about  15  per  cent. 

Nearly  the  whole  of  the  oxygen  thus  taken  up  is  absorbed  by  the 
red  globules;  which  have  a  special  capacity  in  this  respect,  due  to 
their  hemoglobine.  This  is  shown  by  the  fact  that  the  absorbent 

*  Archiv  fur  die  gesammte  Physiologic.     Bonn,  1868,  Band  i.,  p.  279. 


252  FUNCTIONS    OF    NUTRITION. 

capacity  of  the  blood  for  oxygen  depends  on  the  presence  or  absence 
of  the  red  globules.  According  to  Magnus,  while  the  blood  contains 
more  than  twice  as  much  oxygen  as  water  could  hold  in  solution  at  the 
same  temperature,  the  serum  alone  has  no  more  solvent  power  for  this 
gas  than  pure  water ;  and  on  the  other  hand,  defibrinated  blood,  that 
is,  the  serum  and  globules  mingled,  dissolves  as  much  oxygen  as  the 
fresh  blood.  Pfliiger  found,  as  the  average  of  six  observations  on  the 
arterial  blood  of  the  dog,  that  the  oxygen  in  the  entire  blood  was, 
by  volume,  15.6  per  cent.,  while  in  the  serum  alone  there  was  only 
0.2  per  cent.  According  to  the  same  observer,  the  arterial  blood  in 
the  carotid  contains  nearly  though  not  quite  all  the  oxygen  which 
it  is  capable  of  holding  in  solution ;  since  a  specimen  of  dog's  blood 
drawn  directly  from  the  artery  contained  18.8  per  cent,  of  oxygen, 
which  was  only  increased  to  a  little  less  than  20  per  cent,  by  agitation 
with  atmospheric  air.  The  blood,  therefore,  either  does  not  become 
fully  saturated  with  oxygen  in  passing  through  the  lungs,  or  else  a 
little  of  this  gas  has  already  passed  into  some  other  combination  before 
reaching  the  carotid  arteries. 

The  color  of  the  blood  depends  on  the  presence  or  absence  of  oxygen, 
not  on  that  of  carbonic  acid.  Yenous  blood,  shaken  up  with  oxygen 
or  atmospheric  air,  at  once  assumes  the  arterial  tint,  though  its  car- 
bonic acid  may  remain.  According  to  Pfliiger  if  defibrinated  dog's 
blood  be  placed  in  two  flasks,  and  shaken  up,  one  with  pure  oxygen, 
the  other  with  a  mixture  of  oxygen  and  carbonic  acid,  both  specimens 
will  present  the  same  bright  color ;  both  of  them  being  found  on 
analysis  to  contain  nearly  the  same  quantity  of  oxygen,  while  their 
proportions  of  carbonic  acid  are  different.  If  blood  be  drawn  after  the 
animals  have  been  made  to  breathe  pure  oxygen,  or  oxygen  and  car- 
bonic acid  mingled,  it  is  of  the  same  color  in  each  instance;  its 
percentage  of  oxygen  being  the  same,  while  that  of  carbonic  acid  is 
different  in  the  two  cases. 

It  is  the  oxygen,  therefore,  which,  on  being  taken  up  by  the  blood- 
globules,  changes  their  color  from  dark  purple  to  bright  red.  It  passes 
off  with  the  arterial  blood  in  this  condition,  and  is  then  distributed  to 
the  capillary  circulation.  Here,  as  the  blood  comes  in  contact  with  the 
tissues,  its  oxygen  in  great  measure  disappears,  and  its  color,  is  again 
changed  from  arterial  to  venous. 

The  loss  of  oxygen  in  the  capillaries  of  the  general  circulation,  is 
due  to  its  transfer  from  the  blood-globules  to  the  tissues.  Nearly  all 
t  lie  tissues  exert  an  absorbent  power  upon  oxygen,  when  exposed  to 
this  gas  or  to  atmospheric  air.  The  experiments  of  Paul  Bert*  have 
shown  that  the  fresh  tissues,  taken  from  the  body  of  the  recently 
killed  animal  and  exposed  to  the  air  in  closed  vessels,  absorb  oxy-en 
will)  different  degrees  of  intensity,  in  the  following  order,  namely: 
muscles,  brain,  kidneys,  spleen,  testicle,  and  pounded  bones.  Of  these 
the  muscles  arc  the  most  active,  ul>sorl)ini>-  50  cubic  centimetres  of 

*Lepons  sur  la  Physiologie  compurcu  do  la  Respiration.    Paris,  1S70,  p.  46. 


RESPIRATION.  253 

oxygen  for  every  one  hundred  grammes  of  muscular  tissue ;  while  the 
bones  absorb  only  a  little  over  17  cubic  centimetres  for  the  same  weight. 
The  absorbent  capacity  of  the  tissues  for  oxygen  is  even  greater 
than  that  of  the  blood.  This  was  shown  by  the  experiments  of  Spal- 
lanzani,  and  more  recently  by  those  of  Bert.  In  Bert's  experiments, 
three  equal  portions  of  recently  drawn  defibrinated  dog's  blood  were 
placed  in  test-tubes,  a  piece  of  fresh  muscular  tissue  from  the  same 
animal  being  added  to  one  of  them,  a  portion  of  the  spleen-tissue  to 
another,  and  the  third  left  to  itself.  After  a  time  it  was  found  that 
the  tissues  had  abstracted  oxygen  from  the  blood  with  which  they  were 
in  contact,  so  that  in  these  two  specimens  the  quantity  of  oxygen 
remaining  was  less  than  in  the  third,  as  follows  : 

QUANTITY  OF  OXYGEN  BY  VOLUME  REMAINING  IN 

Blood  left  to  itself 18  per  cent. 

Blood  containing  spleen  tissue      ....         12       " 
Blood  containing  muscular  tissue  ...          6       " 

Finally,  successive  analyses  of  the  blood,  as  it  passes  from  the 
arteries  to  the  veins,  show  that  its  loss  of  oxygen  is  mainly  in  the 
capillary  circulation.  In  general,  according  to  Pfliiger,  the  quantity  of 
oxygen,  by  volume,  in  arterial  blood  is  15.6  per  cent.  ;  in  venous  blood 
8  per  cent. ;  that  is,  it  is  reduced  about  one-half  in  the  capillaries  of  the 
general  circulation.  But  in  the  blood  of  the  hepatic  veins,  which  has 
passed  through  a  double  set  of  capillary  vessels,  the  loss  of  oxygen 
is  much  greater.  Bernard*  found  that  in  the  same  dog,  blood  from 
different  parts  of  the  circulatory  system,  yielded  the  following  quantities 

of  oxygen: 

QUANTITY  OF  OXYGEN  BY  VOLUME  IN 

Arterial  blood 18.93  per  cent. 

Venous  blood  from  right  side  of  heart     .        .  9.93       " 

Venous  blood  from  hepatic  veins     .         .         .          2.80       " 

Thus  the  blood-globules  serve  as  carriers  of  oxygen  from  the  lungs 
where  it  is  absorbed,  to  the  tissues  where  it  is  consumed ;  the  first 
object  of  respiration  being  to  supply  oxygen  to  the  blood,  in  order  that 
the  blood  may  supply  it  to  the  tissues. 

Exhalation  of  Carbonic  Acid  by  the  Blood. — The  venous  blood,  as 
it  returns  to  the  heart,  is  charged  with  carbonic  acid  to  such  an  extent 
that  a  portion  of  this  gas  is  exhaled  through  the  pulmonary  mem- 
brane, and  discharged  with  the  breath.  Its  quantity  in  the  blood 
has  not  been  determined  with  the  same  accuracy  as  that  of  oxygen. 
Carbonic  oxide,  which  is  so  efficient  for  the  extraction  of  oxygen  from 
the  blood,  displaces  only  a  portion  of  its  carbonic  acid;  and  in  the 
experiments  of  Bernard,  the  maximum  quantity  of  carbonic  acid 
obtained  from  venous  blood  by  this  means  was  only  about  6.5  per  cent. 
A  much  larger  proportion  may  be  extracted  by  the  mercurial  air-pump, 
amounting  on  the  average,  in  the  experiments  of  Ludwig,  to  about  28 

*  Liquides  de  1'Organisme.     Paris,  1859,  tome  i.,  p.  394. 


254  FUNCTIONS    OF     NUTRITION. 

per  cent,  for  arterial  blood,  and  about  31  per  cent,  for  venous  blood. 
But  a  large  part  of  the  carbonic  acid  obtainable  in  this  way  does  not 
exist  in  the  blood  in  a  free  form,  but  in  combination  with  the  alkaline 
carbonates  of  the  plasma  ;  since  a  watery  solution  of  sodium  bicarbon- 
ate will  lose  a  portion  of  its  carbonic  acid,  and  become  reduced  to  a 
carbonate  by  being  subjected  to  a  vacuum,  or  even  by  agitation  with 
hydrogen  at  the  temperature  of  the  body.  Lehmann*  found  that 
after  the  expulsion  from  ox's  blood  of  all  the  carbonic  acid  removable 
by  the  air-pump  and  a  current  of  hydrogen,  there  still  remained 
0.1628  per  cent,  of  sodium  carbonate,  with  which  a  certain  quantity 
of  the  carbonic  acid  previously  given  off  must  have  been  united  in  the 
form  of  bicarbonate. 

It  is  estimated  by  Bert,  from  the  experiments  of  Fernet,  that  a  por- 
tion of  the  carbonic  acid  of  the  blood  is  in  simple  solution,  and  a  portion 
combined  with  the  alkaline  salts ;  the  blood,  when  artificially  saturated 
with  this  gas,  containing  about  three-fifths  in  a  state  of  solution,  and 
about  two-fifths  in  a  state  of  combination.  We  do  not  know,  how- 
ever, what  this  proportion  is  in  the  living  body;  and  the  large 
amount  of  carbonic  acid  removable  by  a  vacuum  does  not  represent 
accurately  that  which  is  capable  of  exhalation  through  the  pulmo- 
nary membrane.  This  quantity  is  very  much  smaller.  We  know  that, 
on  the  average,  13  cubic  centimetres  of  carbonic  acid  are  discharged 
from  the  lungs,  in  man,  with  each  expiration  ;  and  during  this  interval, 
judging  from  the  capacity  of  the  heart,  and  its  frequency  of  pulsation, 
there  can  hardly  be  less  than  400  cubic  centimetres  of  blood,  pass- 
ing through  the  pulmonary  circulation.  This  would  give  only  a  little 
over  three  per  cent,  as  the  volume  of  carbonic  acid  discharged  from  a 
given  quantity  of  blood  in  respiration.  The  average  results  obtained 
by  extraction  with  the  mercurial  air-pump,  in  the  experiments  of  Lud- 
wig,  give  this  quantity  as  the  actual  difference  between  venous  and 
arterial  blood,  as  follows : 
AVERAGE  QUANTITY  OF  CARBONIC  ACID  REMOVABLE  BY  THE  AIR-PUMP,  FROM 

Venous  blood 31.27  per  cent. 

Arterial  blood 27.99       " 

Difference 3.28      " 

All  the  different  modes  of  analysis,  whether  by  carbonic  oxide,  indif- 
ferent gases,  or  the  air-pump,  though  differing  in  the  quantity  extracted, 
show  that  there  is  less  carbonic  acid  in  arterial  than  in  venous  blood, 
and  accordingly  that  this  gas  is  exhaled  from  the  circulating  fluid  during 
its  passage  through  the  lungs. 

Unlike  oxygen,  the  carbonic  acid  of  the  blood  is  principally  contained 
in  the  plasma,  and  not  in  the  globules ;  since  the  serum  has  nearly  the 
same  capacity  of  absorption  for  this  gas  as  the  entire  blood. 

Source  of  the  Carbonic  Acid  of  the  Blood. — The  source  of  the  car- 
bonic acid  of  the  blood,  as  well  as  the  destination  of  its  oxygen,  is  in 

*  Physiological  Chemistry,  Cavendish  edition.     London,  1854,  vol.  L,  p.  438. 


RESPIRATION.  255 

the  tissues.  Every  organized  tissue,  in  the  recent  condition,  has  the 
power  both  of  absorbing  oxygen  and  of  exhaling  carbonic  acid.  G. 
Liebig  showed  that  frogs'  muscles,  recently  prepared  and  freed  from 
blood,  will  absorb  oxygen  and  discharge  carbonic  acid.  Similar  exper- 
iments with  other  tissues  have  led  to  the  same  result.  It  is  in  their 
substance,  accordingly,  that  the  oxygen  is  consumed,  and  the  carbonic 
acid  takes  its  origin.  But  these  two  phenomena  are  not  immediately 
dependent  on  each  other.  In  some  instances,  living  animals  as  well  as 
fresh  animal  tissues  will  continue,  for  a  time,  to  exhale  carbonic  acid 
in  an  atmosphere  of  hydrogen  or  of  nitrogen,  or  even  in  an  exhausted 
receiver.  Marchand  found  that  frogs  would  live  from  half  an  hour  to 
an  hour  in  pure  hydrogen ;  and  that  during  this  time  they  exhaled  even 
more  carbonic  acid  than  in  atmospheric  air,  owing  probably  to  the 
superior  displacing  power  of  hydrogen  for  this  gas.  While  1000 
grammes'  weight  of  frogs  exhaled  about  0.0 11  gramme  of  carbonic 
acid  per  hour  in  atmospheric  air,  they  exhaled  during  the  same  time 
in  pure  hydrogen  as  much  as  0.263  gramme.  The  same  observer 
found  that  frogs  would  recover  after  having  remained  for  about  half 
an  hour  in  a  nearly  complete  vacuum ;  and  that,  when  killed  by  the 
total  abstraction  of  air,  1000  grammes'  weight  of  the  animals  had 
eliminated  0.600  gramme  of  carbonic  acid.  Similar  facts  were  observed 
by  Spallanzani ;  and  Paul  Bert  *  found  that  while  a  certain  quantity  of 
fresh  muscular  tissue,  in  atmospheric  air,  exhaled,  in  a  given  time,  30 
cubic  centimetres  of  carbonic  acid,  the  same  quantity,  in  pure  hydrogen 
exhaled  23  cubic  centimetres  during  the  same  time.  He  even  found 
that  the  exhalation  of  carbonic  acid  would  continue,  in  an  atmosphere 
of  nitrogen,  from  muscular  tissue  which  had  previously  been  subjected 
for  a  quarter  of  an  hour  to  the  action  of  a  vacuum. 

It  is,  furthermore,  evident  that  in  this  internal  process,  as  in  the 
external  phenomena  of  respiration  by  the  lungs,  the  quantities  of  oxy- 
gen absorbed  and  of  carbonic  acid  exhaled  are  not  always  in  the  same 
relation.  Thus  in  the  experiments  of  Bert  on  the  gases  absorbed  and 
discharged  by  the  tissues,  in  some  instances  the  volume  of  carbonic 
acid  produced  was  greater,  and  in  others  less  than  that  of  the  oxygen 
consumed ;  the  proportions  of  the  two  varying  considerably  in  differ- 
ent cases. 

The  following  list  gives  the  result  of  a  series  of  these  experiments : 

QUANTITY  OF  O  AND  C0a  ABSORBED  AND  EXHALED  DURING  24  HOURS, 
IN  CUBIC  CENTIMETRES. 


By  100  grammes  of 
Muscle 

Oxygen  absorbed. 
50.8 
45.8 

Carbonic  acid  exhaled. 
56.8 
42.8 

Kidneys 
Spleen 
Testicles 

37.0 
27.3 
18.3 

15.6 
15.4 
27.5 

Pounded  bones     . 

17.2 

8.1 

*  Le9ons  sur  la  Physiologic  compared  de  la  Eespiration.     Paris,  1870,  p.  49. 


256  FUNCTIONS    OF    NUTRITION. 

The  production  of  carbonic  acid  by  the  tissues  is  not,  therefore,  an 
immediate  result  of  the  absorption  of  oxygen.  The  precise  mode  in 
which  carbonic  acid  originates  in  the  solid  organs  is  unknown ;  but  it 
is  probably  by  some  decomposition  in  which  a  portion  of  the  carbon 
and  oxygen  separate  from  their  previous  combinations  in  this  form, 
while  the  remaining  elements  unite  to  produce  other  substances  of 
different  composition. 

The  most  palpable  phenomena  of  respiration  consist,  accordingly,  in 
an  interchange  of  gases  between  the  blood  and  the  lungs.  As  the  blood 
on  its  return  to  the  lungs  is  comparatively  poor  in  oxygen  and  abun- 
dant in  carbonic  acid,  it  absorbs  the  former  gas  from  the  pulmonary 
cavity,  and  discharges  the  latter  with  the  expired  air.  These  changes, 
however,  are  incomplete,  both  in  the  air  and  in  the  blood.  The  expired 
air  has  never  lost  the  whole  of  its  oxygen,  and  it  contains  only  about 
4  per  cent,  of  carbonic  acid.  On  the  other  hand,  venous  blood  still 
contains  a  moderate  percentage  of  oxygen  ;  and  a  certain  quantity  of 
carbonic  acid  is  also  present  in  arterial  blood.  It  is  only  the  propor- 
tion of  these  gases  which  is  changed  in  respiration,  the  carbonic  acid 
of  the  blood  being  diminished,  and  its  oxygen  increased,  during  its 
passage  through  the  lungs. 

The  office  of  the  respiratory  apparatus  is  to  afford  ingress  and  egress 
to  oxygen  and  carbonic  acid,  two  substances  which  enter  and  leave 
the  body  in  the  gaseous  form,  but  which  have  no  immediate  relation 
with  each  other,  excepting  that  they  are  absorbed  and  exhaled  by  the 
same  organs.  They  represent  the  beginning  and  the  end  of  a  series 
of  internal  changes,  which  are  among  the  most  important  of  those  con- 
nected with  the  maintenance  of  life. 

Nature  of  Respiration. — If  we  regard  respiration  in  its  gross  results 
we  must  consider  it  as  a  process  of  oxidation.  The  living  body  absorbs, 
on  the  one  hand,  free  oxygen  from  the  atmosphere,  and,  on  the  other, 
takes  into  the  alimentary  canal  organic  substances  as  ingredients  of  the 
food.  These  organic  substances,  after  performing  their  office  in  the 
system,  are  discharged  from  it  partly  under  the  form  of  urea,  but 
mainly  as  carbonic  acid  and  water.  The  final  products  of  excretion 
represent  the  organic  elements  of  the  food,  plus  the  oxygen  which  has 
been  absorbed ;  and  they  return  to  the  inorganic  world  in  a  condition 
of  complete  or  nearly  complete  oxidation.  These  facts  are  incontestible, 
and  they  show  plainly  the  general  relations  of  the  incoming  and  out- 
going materials  of  the  animal  frame. 

But  when  we  endeavor  to  learn  the  place  and  manner  of  this  oxida- 
tion in  the  living  body,  the  attempt  fails.  There  is  no  evidence  of  such 
direct  action  taking  place  in  the  circulating  fluid,  nor  in  any  of  the 
organs  or  tissues.  The  food  in  the  alimentary  canal,  during  di<rcsti<m, 
undergoes  catalytic  transformations  and  solutions,  but  no  oxidation ; 
and  it  is  absorbed  from  the  intestine  with  its  organic  characters  unim- 
paired. In  the  lungs  the  process  of  respiration  consists  in  the  absorp- 
tion of  oxygen  and  exhalation  of  carbonic  acid.  These  two  gases  pass 


RESPIRATION.  257 

each  other  in  the  pulmonary  cavities,  on  their  way  to  and  from  the 
blood ;  neither  of  them  being  produced  or  consumed  in  these  organs. 

In  the  blood,  the  plasma  consists  mainly  of  organic  substances  'in 
solution,  and  oxygen  is  abundant  in  the  globules  in  a  state  of  loose 
combination.  But  the  union  of  the  two  certainly  does  not  take  place 
in  the  blood.  Oxygen  disappears  from  it  in  the  capillary  circulation, 
and  is  replaced  by  carbonic  acid  derived  from  the  tissues.  According 
to  the  view  now  generally  accepted,  the  functions  performed  by  the 
blood  are  rather  physical  than  chemical  in  their  nature.  It  is  a  vehicle 
of  transportation  for  nutritious  matters  from  the  alimentary  canal  to 
various  organs,  and  for  oxygen  and  carbonic  acid  between  the  tissues 
and  the  lungs.  It  collects  or  disseminates  substances  which  have 
already  been  prepared  in  other  parts,  and,  as  a  general  rule,  conveys 
them  unchanged  to  their  destinations.  Even  a  substance  like  pyrogallic 
acid,  so  readily  oxidizable  in  an  alkaline  solution  that  it  is  employed 
for  the  quantitative  determination  of  oxygen  in  the  air,  when  intro- 
duced into  the  animal  system  passes  through  it  without  alteration, 
and  reappears  in  the  urine.*  There  is  no  evidence  that  the  blood 
exerts  anywhere  a  direct  oxidizing  action. 

Finally,  in  the  substance  of  the  tissues  and  organs,  it  is  evident  that 
the  carbonic  acid  which  they  produce  is  not  the  immediate  result  of  the 
absorption  of  oxygen.  Its  continued  exhalation  in  an  atmosphere  of  ni- 
trogen, or  of  other  indifferent  gases,  shows  that  it  originates,  in  all  prob- 
ability, by  a  separation  of  its  elements  from  other  previously  existing 
forms  of  combination.  Furthermore,  the  alteration  of  the  organic 
ingredients,  so  far  as  we  can  follow  them  in  the  living  body,  consists 
largely  of  hydrations  and  dehydrations  under  the  influence  of  the  ani- 
mal ferments.  Glucose,  when  absorbed  from  the  alimentary  canal,  is 
reduced,  by  dehydration  in  the  liver,  to  the  form  of  glycogen,  which, 
in  turn,  is  again  converted  by  hydration  into  soluble  glucose.  The 
formation  of  glycocholic  from  taurocholic  acid  (p.  109)  is  a  dehydration 
with  elimination  of  sulphur,  while  biliverdine  is  produced  from  biliru- 
bine  (p.  101)  by  hydration  with  oxidation.  On  the  other  hand,  the 
derivation  of  urobiline  from  bilirubine  (p.  102)  can  only  be  accomplished 
by  a  reduction  process ;  and  the  formation  of  fat  in  the  body  from  car- 
bohydrates (p.  63)  is  undoubtedly  accompanied  by  the  elimination  of 
carbonic  acid  and  the  production  of  other  substances  at  the  same  time. 
From  all  these  facts  it  appears  that  the  transformation  of  tissue  in 
the  body  is  not  a  simple  act  of  combustion,  regulated  by  the  supply  of 
oxygen  to  the  lungs.  It  is  one  in  which  the  tissues  appropriate  the 
oxygen  conveyed  to  them  by  the  blood,  to  form  intermediate  com- 
pounds, and  in  which  they  finally  eliminate  carbonic  acid  as  the  most 
abundant  product  of  their  retrograde  metamorphosis. 

*Gorup-Besanez.  Lehrbuch  der  Physiologischen  Chemie.     Braunschweig,  1878, 
p.  599.     Ewald.  Die  Lehre  von  der  Verdauung.     Berlin,  1879,  p.  5. 

E 


CHAPTER    V. 

Ay  IMA  L    HE  A  T. 

ONE  of  the  characteristic  properties  of  living  creature?  is  that  of 
maintaining,  more  or  less  constantly,  a  standard  temperature,  not- 
withstanding the  external  changes  of  heat  or  cold  to  which  they  are 
subjected.  If  a  bar  of  iron  or  a  vessel  of  water  be  heated  to  a  tem- 
perature above  that  of  the  surrounding  air,  and  then  left  to  itself,  it 
will  at  once  begin  to  lose  heat  by  radiation  and  conduction ;  and  this 
loss  will  continue  until,  after  a  time,  its  temperature  is  reduced  to  that 
of  the  atmosphere.  It  then  remains  stationary  at  this  point,  unless 
the  atmosphere  should  become  warmer  or  cooler;  in  which  case  a 
similar  change  takes  place  in  the  inorganic  body,  its  temperature  vary- 
ing with  that  of  the  surrounding  medium. 

With  man  and  animals  the  case  is  different.  If  a  thermometer  be 
introduced  into  the  rectum,  or  placed  under  the  tongue,  it  will  indicate 
in  man  a  temperature  of  from  37°  to  38°  C.  (about  100°  F.).*  whether 
the  surrounding  atmosphere  be  warm  or  cooL  This  internal  bodily 
temperature  is  sensibly  the  same  in  summer  and  in  winter.  Although 
the  external  air  may  be  at  the  freezing  point,  the  internal  parts  of  the 
body,  when  examined  by  the  thermometer,  will  indicate  their  usual 
standard  of  warmth ;  and  in  ordinary  summer  weather  the  temperature 
of  the  air  is,  for  the  most  part,  many  degrees  below  that  of  the  living 
body.  As  the  body,  however,  by  exposure  to  such  an  atmosphere  : 
be  constantly  losing  heat  by  radiation  and  conduction,  and  yet  main- 
tains a  standard  temperature,  it  is  plain  that  a  certain  amount  of  heat 
must  be  generated  in  its  interior,  sufficient  to  compensate  for  th 
ternal  loss.  The  internal  heat,  so  produced,  is  known  by  the  name  of 
animal  heat. 

Thus  it  is  by  its  own  internal  heat  that  the  body  is  warmed.  The 
clothing  used  by  man,  and  the  fur,  wool,  or  feathers  by  which  animals 
are  protected,  have  no  warmth  in  themselres :  they  simply  prevent 
the  body  from  losing  heat  too  rapidly,  and  thus  becoming  cooled  down 
below  its  normal  standard.  Even  the  furnaces  and  fires  of  a  dwelling 
house  only  serve  to  moderate  the  cooling  influence  of  the  air ;  for  the 
atmosphere,  even  in  the  warmest  apartment,  never  rises  to  the  heat 
of  the  living  body,  which  is  still  the  only  source  of  its  own  vital 
temperature, 

Difference  of  Temperature  in  Different  Classes  of  Animate. — The 

*  To  convert  degrees  of  the  Centigrade  scale  into  the  corresponding  value  tor  the 
Fahrenheit  scale,  multiply  by  1.8  and  add  32  to  the  product. 

M 


ANIMAL     HEAT.  259 

production  of  internal  heat  varies  in  intensity  in  different  classes  of 
animals.  As  a  rule,  it  is  most  active  in  birds,  whose  temperature 
is  in  general  45 c  C.  In  mammalians  it  >  :  and  in  man 

about  37.5-.  As  in  these  two  classes  the  internal  organs  and  the  blood 
are  nearly  always  above  the  temperature  of  the  air  or  that  of  the  skin, 
and,  accordingly,  feel  warm  to  the  touch,  they  are  called  "  warm-blooded 
animals."  In  reptiles  and  fish,  on  the  other  hand,  the  production  of 
heat  is  much  less  rapid,  and  preponderates  so  little  over  that  of  the  air 
or  water  which  they  inhabit,  that  no  marked  difference  is  perceptible 
on  cursory  examination ;  and  as  their  internal  organs  have  a  lower 
temperature  than  our  own  integument,  and  consequently  feel  cool  to 
the  touch,  they  are  called  "cold-blooded  animals."  This  difference, 
however,  is  only  in  degree  and  not  in  kind.  Reptiles  and  fish  also 
generate  a  certain  amount  of  heat,  which  may  be  measured  by  the  ther- 
mometer. The  temperature  of  frogs,  serpents,  tortoises,  water-lizards, 
and  fish  has  been  found  to  be  from  1.7-  to  4.5°  above  that  of  the  sur- 
rounding air  or  water. 

In  invertebrate  animals  the  heat  produced  is  usually  still  less  percep- 
tible because,  from  the  greater  surface  of  their  bodies  in  proportion  to 
their  mass,  the  warmth  is  more  rapidly  dissipated.  But  when  many 
of  them  are  collected  in  a  small  space,  and  especially  when  in  a  state 
of  activity,  their  heat  is  distinguishable  by  thermometric  measurement. 
The  temperature  of  the  butterfly  after  active  motion  has  been  found 
from  •_  "  :o  5°  above  that  of  the  air;  that  of  the  humble-bee  from 
1.5:  :o  5.-?:  higher  than  the  exterior.  According  to  Newport,  the 
interior  of  a  hive  of  bees  may  have  a  temperature  of  9°  with  the 
external  atmosphere  at  1.4°,  even  while  the  insects  are  quiet ;  but  if 
they  be  excited  by  tapping  on  the  hive,  it  may  rise  to  38.8-.  Thus 
so  long  as  the  insects  are  at  rest,  the  thermometer  indicates  a  very 
moderate  warmth ;  but  if  kept  for  a  few  moments  in  rapid  motion  in  a 
confined  space,  they  may  generate  sufficient  heat  to  produce  a  sensible 
elevation  of  temperature. 

The  production  of  heat  is  not  confined  to  animals,  but  takes  place 
also  in  vegetables.  In  vegetables,  however,  it  is  very  rapidly  lost, 
owing  to  the  extensive  surface  presented  by  their  ramifications  and 
foliage,  and  the  abundant  evaporation  of  moisture.  If  this  loss  be 
diminished  by  keeping  the  air  charged  with  watery  vapor  and  thus 
preventing  evaporation,  the  elevation  of  temperature  becomes  sensible 
and  may  be  measured.  Dutrochet*  demonstrated,  by  the  use  of  the 
thermo-electric  needle,  that  nearly  all  parts  of  a  living  plant,  such  as 
the  green  stems,  the  leaves,  the  buds,  and  even  the  roots  and  fruit, 
generate  heat  to  some  degree ;  the  maximum  temperature  thus  reached 
being  about  0.28°  above  that  of  the  surrounding  atmosphere.  Sub- 
sequent observations  have  shown  that  in  certain  periods  of  vegeta- 
:\s  in  those  of  germination  and  flowering,  the  development 

*  Annales  des  Sciences  naturelles.     Paris,  2me  Serie,  tome  liL,  p.  -" " 


260  FUNCTIONS    OF    NUTRITION. 

of  heat  is  much  more  rapid.  In  the  malting  of  barley,  when  a  con- 
siderable quantity  of  germinating  grain  is  piled  in  a  mass,  its  elevation 
of  temperature  may  be  distinguished,  both  by  the  hand  and  the  ther- 
mometer. The  most  abundant  heat-production  by  vegetables  is  in  the 
flowers  of  the  Aracesa  (Calla,  Indian  turnip,  Sweet  flag)  at  the  time 
of  fecundation,*  which  sometimes  show  a  temperature  of  from  5°  to 
10°  above  that  of  the  surrounding  air. 

The  generation  of  heat  is,  accordingly,  a  phenomenon  common  to  all 
living  organisms.  When  the  mass  of  the  body  is  large  in  proportion 
to  its  extent  of  surface,  its  heat  is  readily  perceptible  both  by  the 
touch  and  by  the  thermometer.  la  birds  and  mammalians  the  heat 
production  is  more  active  than  in  reptiles  and  fish ;  and  even  in  differ- 
ent species  of  the  same  class,  it  differs  in  degree  according  to  the 
special  organization  of  the  animal  and  the  general  activity  of  its 
functions. 

Quantity  of  Heat  in  the  Living  Body. — The  quantity  of  heat  pro- 
duced in  the  body  within  a  given  time  is  measured  by  the  increase  of 
temperature  which  it  produces  in  a  known  volume  of  water.  Draperf 
found  that  the  human  body,  with  a  volume  of  about  85  litres  (3  cubic 
feet)  and  a  weight  of  81.65  kilogrammes  (180  pounds  avoirdupois),  by 
remaining  in  the  bath  for  one  hour,  could  raise  the  temperature  of  212 
kilogrammes  of  water  1.11°  ;  which  he  estimates,  assuming  the  specific 
heat  of  the  body  to  be  about  the  same  with  that  of  water,  would  be 
capable  of  warming  the  body  itself  2.77°.  But  as  the  temperature  of 
the  body,  in  the  observation  quoted,  was  lowered  0.55°  while  in  the 
bath,  the  heat  actually  generated  would  be  capable  of  warming  the 
body,  or  an  equal  volume  of  water,  2.22°.  This  would  be  equivalent 
to  188.7  heat  units,!  produced  by  the  human  body  in  the  course  of  one 
hour,  or  2.31  heat  units  for  every  kilogramme  of  bodily  weight. 

In  the  experiments  of  Senator  §  on  the  heat-producing  power  in  dogs, 
the  animals  were  inclosed  in  a  copper  cage,  through  which  ventilation 
was  kept  up  at  a  known  rate,  the  temperature  of  the  incoming  and 
outgoing  air  being  noted  at  short  intervals.  The  cage  was  surrounded 
by  a  known  volume  of  water,  at  from  26.5°  to  29°  C.,  and  the  whole 
apparatus  inclosed  in  an  outer  case  made  as  non-conducting  as  possible ; 
the  heat  actually  lost  from  it  being  determined  by  preliminary  obser- 
vation. The  internal  temperature  of  the  animal  having  been  taken, 
he  was  introduced  into  the  cage  and  allowed  to  remain  for  a  certain 
time.  The  heat  produced  was  ascertained  by  the  increase  of  temper- 
ature in  the  water  surrounding  the  cage,  the  result  being  corrected 
by  that  of  the  air  used  for  ventilation,  as  well  as  by  the  variation  in 

*  Sachs,  Traite  de  Botanique.    Paris,  1874,  p.  847. 

f  American  Journal  of  Science  and  Arts.     New  Haven,  1872,  vol.  ii.,  p.  445. 

j  A  heat  unit  is  the  quantity  of  heat  required  to  raise  the  temperature  of  one  kilo- 
gramme of  water  from  0°  to  1°  of  the  Centigrade  scale. 

%  Archiv  fiir  Anatomic,  Physiologic,  und  wissenschaftliche  Medicin.  Leipzig, 
1872. 


ANIMAL    HEAT.  261 

temperature  of  the  animal,  and  the  loss  from  the  apparatus  by  external 
cooling.  By  this  method  it  was  found,  as  the  average  result  of  five 
observations,  that  a  dog  of  5.392  kilogrammes'  weight,  at  rest  and  in 
the  fasting  condition,  produced  in  one  hour  12.63  heat  units;  that  is, 
2.34  heat  units  for  every  kilogramme  of  bodily  weight.  According 
to  these  experiments,  the  heat-producing  power  in  the  dog  and  that 
in  man  are  nearly  the  same ;  that  of  the  dog  being  rather  the  more 
active  of  the  two. 

Normal  Variation  of  Temperature  in  the  Living  Body. — The  tem- 
perature of  the  body  is  not  the  same  throughout,  but  increases,  for  a 
certain  distance,  from  the  exterior  toward  the  central  parts.  Like  any 
other  substance  of  higher  temperature  than  the  air,  the  animal  body 
is  constantly  losing  heat  from  its  surface ;  so  that  the  integument  and 
the  parts  immediately  subjacent,  which  are  more  exposed  to  this  cool- 
ing influence  than  the  internal  organs,  have  a  temperature  slightly 
below  that  of  the  body  in  general.  Accordingly,  whenever  the  external 
air  rises  to  the  neighborhood  of  37°  or  37.5°  C.,  it  feels  uncomfort- 
ably warm;  because,  although  this  is  the  normal  temperature  of  the 
internal  organs,  it  is  considerably  above  that  of  the  skin,  which  is 
readily  sensitive  to  variations  of  cold  or  warmth.  The  cooling  influ- 
ence of  the  atmosphere  is,  however,  moderated  by  the  circulatory  move- 
ment of  the  blood ;  since  the  warmer  blood  coming  from  the  internal 
parts  supplies  the  integument  with  fresh  quantities  of  heat,  and  thus 
tends  to  compensate  for  its  external  loss. 

But  notwithstanding  this  compensation,  the  difference  in  temperature 
between  the  external  and  internal  parts  of  the  body  is  always  per- 
ceptible during  health.  If  the  bulb  of  a  thermometer  be  held  for  some 
minutes  between  the  folds  of  skin  in  the  palm  of  the  hand,  it  will 
stand  at  36.4°  ;  in  the  axilla,  at  36.6°  ;  under  the  tongue,  it  will  reach 
37.2°  ;  in  the  rectum,  37.5°  ;  and  Dr.  Beaumont  found,  in  the  case  of 
Alexis  St.  Martin,  that  the  thermometer,  introduced  into  the  stomach 
through  the  gastric  fistula,  often  indicated  a  temperature  of  3T.8°.  It 
is  evident  that,  in  order  to  ascertain  the  internal  temperature  of  the 
body,  the  bulb  of  the  thermometer  should  be  inserted  so  deeply  as  to 
pass  beyond  the  superficial  zone  affected  by  the  process  of  external 
cooling.  Even  when  beneath  the  tongue  it  is  in  contact  with  parts 
which  are  slightly  cooled  by  the  passage  of  the  air  in  respiration, 
and  accordingly  does  not  reach  the  maximum  temperature  of  the  body. 
For  this,  it  must  be  so  deeply  inserted  into  the  abdominal  cavity  or  the 
rectum,  that  a  further  introduction  produces  no  increase  in  the  indicated 
temperature.  This  is  the  method  usually  adopted  in  physiological 
observations. 

Beside  the  difference  from  the  above  cause  between  the  surface  and 
the  interior,  the  internal  temperature  also  varies  within  narrow  limits, 
according  to  different  physiological  conditions.  Jiirgensen  *  has  shown 

*  Die  Korperwarme  des  gesunden  Menschen.     Leipzig,  1873. 


262  FUNCTIONS    OF    NUTRITION. 

that  in  man  there  is  a  diurnal  variation,  the  temperature  during  the 
day  being  a  little  higher  than  at  night,  even  when  both  periods  are 
passed  in  complete  repose.  A  series  of  observations  on  the  same  indi- 
vidual in  a  state  of  rest  gave  the  following  averages : 

TEMPERATUKE  OF  THE  HUMAN  BODY  WHEN  AT  REST. 
By  day.  By  night. 

37.34°  36.91° 

The  difference  between  the  two  averages  amounts  to  0.43°.  There 
are  also  temporary  variations  of  small  extent  during  each  of  the  above 
periods ;  the  greatest  variation  during  the  day  being  0.27°  ;  that  during 
the  night  0.15°. 

The  temperature  of  the  body  is  also  increased  by  muscular  activify. 
It  is  a  matter  of  common  observation,  both  in  man  and  animals,  that 
temporary  exertion  produces  an  increase  of  bodily  warmth.  Jurgensen 
observed  in  the  same  individual  that  while  during  a  day  of  absolute 
rest,  the  maximum  temperature  attained  was  37.7°,  under  the  influence 
of  exercise  it  reached  38.8°.  A  much  more  striking  difference,  corre- 
sponding with  muscular  repose  or  activity,  has  already  been  mentioned 
as  observable  in  insects. 

The  animal  temperature  is  furthermore  increased  or  diminished  by  a 
condition  of  digestion  or  abstinence.  This  was  indicated  in  several 
instances  by  the  observations  of  Jurgensen  on  man,  but  is  shown  in 
a  marked  degree  by  those  of  Senator  on  the  dog,  in  which  the  pro- 
duction of  heat  was  sensibly  diminished  by  fasting,  and  increased  by 
food.  The  following  table  shows  the  heat  produced  by  the  same  animal 
under  these  two  conditions : 

QUANTITY  OF  HEAT  PRODUCED  BY  THE  DOG  IN  ONE  HOUR. 

After  two  days'  fasting 10.90  heat  units. 

After  one  day's  fasting 12.63 

One  hour  after  feeding 18.87 

As  the  production  of  animal  heat  can  only  take  place  by  the  con- 
sumption or  alteration  of  the  bodily  ingredients,  it  is  evident  that 
during  abstinence  from  food,  the  materials  susceptible  of  this  change 
must  diminish  in  quantity  ;  and  the  temperature  of  the  body  after  a 
time  becomes  lowered,  owing  to  a  deficiency  in  its  sources  of  supply. 

Mode  of  Production  of  Animal  Heat. 

In  all  instances,  so  far  as  observation  goes,  the  production  of  heat  in 
living  organisms  is  in  proportion  to  the  activity  of  their  internal  changes. 
These  changes  are  especially  indicated  by  the  absorption  of  oxym-n 
and  the  exhalation  of  carbonic  acid.  Even  in  vegetables,  it  has  been 
demonstrated  that  the  absorption  of  oxygen  is  always  accompanied  by 
the  exhalation  of  carbonic  acid  and  the  production  of  heat ;  and  the 
quantity  of  heat  produced  is  greatest  during  the  processes  of  germina- 
tion and  flowering,  which  are  accompanied  by  the  most  active  absorp- 
tion and  exhalation  of  oxygen  and  carbonic  acid  respectively. 


ANIMAL    HEAT.  263 

A  similar  relation  is  manifest  in  the  animal  kingdom.  Birds  and 
mammalians,  whose  respiration  is  most  active,  have  the  highest  temper- 
ature ;  while  in  reptiles  and  fish,  where  the  respiration  is  sluggish,  the 
production  of  heat  is  also  less  abundant.  The  connection  between  the 
two  phenomena  is  especially  observable  in  hibernating  animals,  in 
which,  during  the  winter  sleep,  respiration  becomes  comparatively  inac- 
tive, and  the  bodily  temperature  is  reduced  to  a  very  low  standard. 
In  the  observations  of  Horvath*  on  marmots,  he  found  that  these 
animals  during  cold  weather  are  plunged  in  a  profound  stupor,  in  which 
their  respiration  is  very  infrequent  and  sometimes  hardly  perceptible. 
At  certain  intervals  they  awake  for  a  short  time,  and  again  return  to 
the  state  of  insensibility.  The  internal  temperature  of  the  animal,  when 
awake,  was  from  35°  to  37°  C. ;  while,  in  the  hibernating  condition,  it 
was  reduced  to  10°,  9°,  or  even  to  2°,  according  to  that  of  the  sur- 
rounding air.  On  awaking,  the  temperature  rapidly  rises.  In  one 
anima.1,  during  sleep,  it  was  from  9°  to  10°  ;  but  on  awaking  it  rose 
in  one  hour  to  12°,  in  two  hours  to  If  °,  and  in  two  hours  and  a  half 
to  32°.  Respiration  varies  in  activity  to  a  similar  degree.  A  marmot 
weighing  153  grammes  produced,  while  in  the  comatose  condition, 
0.015  gramme  of  carbonic  acid  per  hour;  and  two  days  afterward, 
when  awake,  produced  0.513  gramme  in  the  same  time,  that  is,  more 
than  thirty  times  as  much  as  when  in  the  state  of  hibernation. 

These  facts  indicate  so  close  a  relation  between  the  intensity  of  res- 
piration and  that  of  heat  production,  that  either  one  of  these  processes 
may  be  taken,  in  general  terms,  as  the  measure  of  the  other ;  particu- 
larly as  respiration  consists  in  the  absorption  of  oxygen  and  the  exhala- 
tion of  carbonic  acid,  and  as  the  oxidation  of  carbonaceous  matters, 
outside  the  body,  is  one  of  our  readiest  means  for  the  production  of 
heat. 

But  respiration  is  not  exclusively  connected  with  heat-production. 
It  is  essential  to  all  the  manifestations  of  animal  life,  and  may  be  taken 
as  the  criterion  of  vital  activity  in  general ;  and  a  further  study  of 
its  phenomena  shows  that  the  heat  of  the  living  body  cannot  be  con- 
sidered as  due  to  direct  oxidation. 

The  Evolution  of  Heat  and  the  Products  of  Respiration  not  strictly 
proportional.  —  Notwithstanding  the  general  relation  in  activity 
between  respiration  and  heat-production,  a  comparison  of  the  quan- 
tity of  heat  produced,  and  that  of  oxygen  absorbed  or  of  carbonic 
acid  exhaled,  under  different  circumstances,  shows  that  they  do  not 
exactly  correspond  with  each  other.  In  the  observations  of  Senator 
on  dogs,  the  evolution  of  heat  and  the  production  of  carbonic  acid  did 
not  follow  the  same  rate  of  increase.  They  were  both  augmented 
during  digestion,  but  the  production  of  carbonic  acid  never  increased 
to  the  same  degree  with  that  of  heat.  The  averages  obtained  in  three 
series  of  observations  gave  the  following  result : 

*  Revue  des  Sciences  Medicales.     Paris,  1873,  tome  i.,  p.  59. 


264  FUNCTIONS    OF    NUTRITION. 

QUANTITIES  OF  HEAT  AND  OF  CAKBONIC  Acin  PRODUCED  BY  THE  DOG  IN  ONE  Horn. 
Condition  Carbonic  acid  in  Proportion 

of  the  animal.  grannno.  Heat  units.  between  the  two. 

(Fasting     ....       3.455  12.630  1  to  3.65 

Dog  No.  1  |jn  digegtion  t     m     m      5i0l3  18.875  1  to  3.76 

(Fasting    ....       4.405  16.500  1  to  3.72 

Dog  No.  2  jln  digestion  m     f     f      4.837  19e390  i  to  4-0l 

(Fasting     ....       3.154  16.880  1  to  5.35 

Dog  No.  3  jln  digestion  .     .    t      3i846  21.960  1  to  5.71 

Thus  the  proportion  of  carbonic  acid  formed  to  the  heat  produced  is 
different  in  the  three  animals  when  compared  with  each  other  in  the 
same  condition  ;  and  it  also  varies  in  each  animal  under  the  different 
conditions  of  fasting  and  digestion. 

The  same  observer  found  that  under  the  influence  of  a  low  tempera- 
ture in  a  state  of  repose,  the  production  of  heat  was  never  increased, 
but  was  usually  diminished ;  while  that  of  carbonic  acid  was  generally 
somewhat  increased  and  never  diminished. 

Local  Production  of  Heat  in  the  Organs  and  Tissues. — Although 
the  body,  as  a  whole,  presents  a  general  standard  temperature,  its  heat 
is  produced  in  each  separate  organ  and  tissue  by  the  local  acts  of  nutri- 
tion. This  is  shown  by  the  fact  that  each  organ  has  a  special  tempera- 
ture of  its  own,  which  increases  or  diminishes  according  to  its  condi- 
tion of  activity  or  repose.  A  large  quantity  of  heat  is  produced  in 
the  substance  of  the  muscles.  In  the  experiments  of  Becquerel  and 
Breschet,  the  temperature  of  the  brachialis  muscle,  in  a  man,  during 
repose  was  36.5°  ;  but,  after  repeated  and  energetic  flexion,  it  was  from 
37°  to  37.5°.  Bernard,*  by  placing  thermo-electric  needles  in  the  gas- 
trocnemii  muscles  of  a  dog,  after  section  of  the  spinal  cord  to  prevent 
voluntary  movements,  found  the  temperature  of  the  muscles  on  the 
two  sides  sensibly  equal ;  but  on  producing  contraction  by  galvanizing 
one  sciatic  nerve,  the  temperature  of  the  muscle  on  that  side  was 
increased  0.1°  or  0.2°,  while  the  venous  blood  returning  from  it  became 
darker  in  hue.  Since  the  muscles  constitute  so  large  a  part  of  the 
mass  of  the  body,  it  is  evident  that  continuous  muscular  exertion 
must,  after  a  time,  produce  a  general  elevation  of  temperature.  In  the 
muscles,  during  contraction,  the  increase  in  warmth  is  accompanied  by 
greater  consumption  of  oxygen,  and  consequently  by  a  darker  color  of 
their  venous  blood. 

Heat  is  also  produced  in  the  glandular  organs  when  in  active  secre- 
tion, as  shown  by  the  temperature  of  the  blood  entering  and  leaving 
their  tissue.  Under  these  circumstances  the  venous  blood  coming  from 
the  ghui'l  is  warmer  than  the  arterial  blood  with  which  it  is  supplied. 
According  to  the  observations  of  Bernard  on  the  dog,  while  the  sub- 
maxillary  gland  is  in  repose,  its  circulation  is  slow,  and  its  venous 
blood  scanty  and  dark-colored  ;  the  oxygen  of  the  blood  being  reduced, 

*  Revue  Scientifi  pie.     Paris,  1871,  No.  1,  p.  1064. 


ANIMAL     HEAT.  265 

while  traversing  the  organ,  to  40  per  cent,  of  its  original  quantity.  But 
when  the  gland  is  excited  to  active  secretion,  its  circulation  is  increased 
in  rapidity,  and  its  venous  blood  more  abundant  and  brighter  in  color ; 
its  oxygen  being  only  reduced  to  61  per  cent,  of  that  in  arterial  blood! 
At  the  same  time  the  temperature  of  the  gland  rises,  notwithstanding 
that  its  consumption  of  oxygen  is  less  than  in  a  condition  of  repose. 

A  similar  elevation  of  temperature  takes  place  in  the  blood  while 
traversing  the  capillary  circulation  of  the  intestine  and  of  the  liver. 
The  following  tables  give  the  results  of  two  series  of  observations  by 
Bernard  on  the  temperature  of  the  blood  entering  and  leaving  these 
organs  in  the  dog  : 

TEMPERATURE  OF  THE  BLOOD  ra  THE 
Aorta.  Portal  Vein. 

36.8°  38.8° 

40.3°  4-0.7° 

39.4°  39.5° 

Portal  Vein.  Hepatic  Vein. 
40.2°  40.6° 

40.6°  40.9° 

40.7°  40.9° 

Thus  the  blood  of  the  hepatic  vein,  after  traversing  two  successive 
capillary  circulations,  is  warmer  than  that  in  any  other  part  of  the 
body. 

Even  in  the  kidneys,  when  the  secretion  of  urine  is  active,  there  is  a 
rise  of  temperature  in  the  blood  of  the  renal  veins.  At  the  same  time, 
as  in  the  submaxillary  glands,  the  circulation  is  increased,  the  venous 
blood  leaves  the  organ  of  a  bright  red  color,  and  its  proportion  of 
oxygen,  according  to  Bernard,  is  only  reduced  to  88  per  cent,  of  that 
contained  in  the  arteries,  while  in  the  condition  of  glandular  repose  it 
is  reduced  to  33  per  cent. 

It  is  evident,  therefore,  that  animal  heat  may  be  derived  from  other 
causes  than  the  immediate  consumption  of  oxygen  and  formation  of 
carbonic  acid.  Even  outside  the  body  heat  may  be  produced  by  the 
hydration  of  quick-lime,  or  by  the  mixture  of  water  with  alcohol  or 
sulphuric  acid;  and  the  changes  of  nutrition,  consisting  largely  of 
hydrations,  and  other  chemical  or  physical  actions  in  which  direct  oxi- 
dation does  not  take  part,  are  sufficient  to  account  for  the  heat-produc- 
tion within  the  living  frame.  This  heat-production  is  a  local  process, 
and  takes  place  with  different  degrees  of  intensity  according  to  special 
acts  of  nutrition  in  different  organs.  In  the  muscles  it  is  accompanied 
by  increased  consumption  of  oxygen  and  deeper  coloration  of  the 
venous  blood ;  in  the  salivary  glands  and  the  kidneys  by  diminished 
consumption  of  oxygen  and  a  less  complete  change  in  the  color  of  the 
blood.  The  temperature  of  the  blood  coming  from  each  organ  is  in 
proportion  to  the  activity  of  heat-production  in  the  organ  itself;  that 
of  the  venous  blood  consequently  varies  in  different  parts,  while  that 
of  arterial  blood  is  everywhere  sensibly  the  same. 


266  FUNCTIONS    OF    NUTRITION. 

Cooling  of  the  Blood  in  the  Lungs  and  Skin. — While  in  the  other 
internal  organs  the  blood  is  warmed  during  its  passage  through  the 
capillary  vessels,  in  the  lungs  its  temperature  is  slightly  diminished. 
This  fact,  which  has  been  alternately  asserted  and  denied,  owing  to  the 
difficulty  of  excluding  incidental  causes  of  error,  has  been  abundantly 
confirmed  by  the  observations  of  Hering,  Bernard,  Hcidenhain  and 
Korner,  and  Strieker  and  Albert.  That  of  Hering  was  made  on  a  young 
calf,  otherwise  in  good  condition,  but  having  the  malformation  of  ectopia 
cordis,  so  that  the  heart  was  unaffected  by  the  contact  of  other  organs. 
In  this  case  the  blood  of  the  right  ventricle  had  a  temperature  of  39.37°, 
that  of  the  left  ventricle  38.75°.  Heidenhain  and  Korner,*  in  94  obser- 
vations on  the  dog,  partly  with  thermo-electric  needles  and  partly  with 
the  mercurial  thermometer,  found  the  temperature  of  the  blood  equal  on 
the  two  sides  of  the  heart  in  only  one  instance.  In  all  the  others,  it 
was  higher  on  the  right  side  than  on  the  left,  by  0.1°  to  0.6°.  Ber- 
nard,! who  first  demonstrated  this  difference  by  the  mercurial 
thermometer,  has  shown  it  also  by  the  use  of  thermo-electric  needles, 
introduced  into  the  right  and  left  ventricles  of  the  dog's  heart,  through 
the  jugular  vein  and  carotid  artery  respectively ;  always  finding  the 
blood  in  the  right  ventricle  warmer  than  that  in  the  left.  According 
to  these  observations,  the  difference  in  temperature  may  amount  in  the 
fasting  animal  to  0.174°,  during  digestion  to  0.232°.  Although  during 
digestion  the  temperature  of  the  blood  generally  is  higher  than  in  the 
fasting  condition,  the  difference  between  the  two  sides  of  the  heart 
continues  to  show  itself  in  the  same  direction. 

The  diminution  in  temperature  of  the  blood  while  passing  through 
the  lungs  is  usually  attributed  to  the  cooling  influence  of  the  air  in 
the  pulmonary  cavities  and  to  the  vaporization  of  watery  fluid.  As 
the  air  expelled  by  respiration  is  warmer  than  when  introduced  into 
the  lungs,  it  must  withdraw  a  certain  amount  of  heat  from  the  internal 
parts  ;  and  as  it  contains  watery  vapor  disengaged  from  the  lungs,  the 
vaporization  of  this  fluid  must  also  reduce  the  temperature  of  the 
organs.  Whether  these  causes  are  more  or  less  than  sufficient  to  account 
for  the  difference  in  the  blood  on  the  two  sides  of  the  heart  has  not  been 
determined.  It  is  possible  that  a  certain  amount  of  heat  is  produced  in 
the  lungs,  as  in  other  internal  organs ;  and  that  the  heat  so  produced  is 
more  than  counterbalanced  by  that  lost  from  the  pulmonary  surface,  the 
total  effect  on  the  blood  being  consequently  a  lowering  of  its  temper- 
ature. In  the  cutaneous  circulation  similar  causes  exist  for  a  cooling 
effect  on  the  blood ;  namely,  the  contact  of  the  air,  and  the  vapori- 
zation of  watery  fluid  supplied  by  perspiration.  It  is  for  this  reason 
that  the  superficial  parts  of  the  body  are  less  warm  than  the  interior ; 
and  accordingly  the  blood,  after  passing  through  the  vessels  of  the  integ- 
ument, returns  to  the  centre  with  its  temperature  slightly  diminished. 


*  Archiv  fur  die  gesammtr  Physiologies     Bonn,  1871,  Band  iv.,  p.  558. 
f  Revue  Scientifique.    Paris,  1871,  No.  1,  p.  946. 


I 


ANIMAL    HEAT.  267 

The  amount  of  warmth  thus  lost  will  vary  with  the  degree  of  external 
cold  and  other  conditions  influencing-  the  abstraction  of  heat. 

Local  Elevation  of  Temperature  by  Increased  Circulation. If  the 

circulation  be  increased  in  any  part  of  the  integument,  the  effect  pro- 
duced is  a  local  rise  of  temperature.  This  was  shown  by  Bernard  in 
his  experiments  on  division  of  the  sympathetic  nerve.  In  the  rabbit 
this  operation  produces  a  relaxation  of  the  blood-vessels  on  the  corre- 
sponding side  of  the  head,  an  increased  vascularity  of  the  parts,  most 
readily  seen  in  the  semi-transparent  tissues  of  the  ear,  and  a  higher 
temperature,  perceptible  both  by  the  touch  and  by  the  thermometer. 
After  section  of  the  sympathetic  nerve  on  the  right  side,  the  tempera- 
ture of  the  corresponding  ear  was  increased  from  25°  to  32°  C. ;  the 
difference  between  the  two  sides  being  usually  more  marked  in  a  cold 
atmosphere.  As  the  superficial  parts  of  the  body  are  habitually  cooler 
than  the  internal,  from  their  exposure  to  the  air,  and  as  they  are 
constantly  supplied  with  warm  blood  from  the  interior,  their  tempera- 
ture will  be  raised  by  an  increase  in  the  amount  of  blood  circulating 
through  them.  The  rise  of  temperature  in  these  cases  is  a  passive  one, 
the  exposed  tissues  being  warmed  at  the  expense  of  the  blood  coming 
from  the  interior.  No  more  heat  is  produced,  than  usual,  and  the  cooling 
effect  of  the  air  on  the  surface  is  unchanged ;  but  it  is  less  perceptible 
in  the  part  subjected  to  experiment,  owing  to  its  increased  supply  of 
blood,  and  the  larger  quantity  of  heat  brought  to  it  in  a  given  time. 

The  influence  of  the  circulation  upon  the  temperature  of  the  external 
parts  has  been  shown  by  Mitchell  *  in  observations  on  the  human 
subject.  If  the  hand  and  arm  be  held  for  some  moments  above  the 
head,  emptied  as  fully  as  possible  of  blood,  and  a  tourniquet  then 
applied  to  the  arm  in  such  a  way  as  to  check  the  circulation,  the  tem- 
perature of  the  hand  falls  0.55°.  If  on  the  contrary,  the  circulation 
be  left  unimpeded,  and  a  freezing  mixture  applied  to  the  elbow,  suffi- 
cient to  chill  the  ulnar  nerve,  when  sensation  has  become  entirely 
abolished  the  temperature  of  the  corresponding  hand  rises  1.10°  or 
even  2.20°.  But  if  the  arm  be  emptied  of  blood,  the  tourniquet 
applied,  and  the  ulnar  nerve  then  chilled  to  insensibility,  the  temper- 
ature of  the  hand  no  longer  rises,  but  falls,  as  before,  0.55°.  This 
shows  that  the  rise  of  temperature,  in  the  second  experiment,  was  due 
to  increased  circulation  of  blood  in  the  paralyzed  parts. 

In  the  glandular  organs,  on  the  other  hand,  when  in  functional  activ- 
ity, the  rise  of  temperature  is  an  active  one,  taking  place  in  the  sub- 
stance of  the  gland  itself;  since  the  blood  passing  through  these  organs 
becomes  warmer  instead  of  cooler,  and  receives  heat  from  changes 
taking  place  in  the  glandular  tissue. 

Equalization  of  Bodily  Temperature  by  the  Circulation. — As  the 
production  of  heat  varies  in  different  parts,  according  to  their  nutritive 
changes,  the  blood  acquires  a  higher  temperature  in  some  organs  than 

*  Archives  of  Scientific  and  Practical  Medicine.    New  York,  1873,  vol.  i.,  p.  354. 


268  FUNCTIONS    OF    NUTRITION. 

in  others ;  while  in  the  lungs  and  skin  its  heat  diminishes  instead  of 
increasing.  If  the  blood  remained  at  rest,  these  differences  would  be 
still  more  marked.  But  as  it  is  in  constant  motion,  from  the  circum- 
ference to  the  centre,  and  again  from  the  centre  to  the  circumference, 
the  effect  of  the  circulation  is  to  equalize,  in  great  measure,  the  temper- 
ature of  different  parts.  The  blood  coming  from  the  general  integu- 
ment with  a  diminished  temperature  is  mingled  writh  that  of  the  mus- 
cular system,  which  has  become  warmed  during  its  capillary  circulation. 
The  blood  of  the  hepatic  veins,  which  is  the  warmest  of  all,  joins  the 
current  of  the  inferior  vena  cava,  with  a  somewhat  lower  temperature, 
returning  from  the  pelvic  organs  and  the  inferior  extremities.  It  is 
again  mingled,  at  its  entrance  into  the  right  cavities  of  the  heart,  with 
the  blood  descending  from  the  head  and  upper  extremities  by  the  supe- 
rior vena  cava.  The  whole  volume  of  the  blood  then  passes  through  the 
lungs,  with  the  effect  of  still  further  moderating  its  temperature ;  and 
the  arterial  blood  is  distributed  to  the  various  parts  of  the  body,  to  gain 
warmth  in  some  and  to  lose  it  in  others,  and  to  be  again  mingled  after 
a  few  seconds  at  the  centre  of  the  circulation.  The  superabundant 
heat  of  certain  organs,  where  its  production  is  most  active,  is  con- 
stantly transferred  to  others  by  the  moving  column  of  the  blood ;  and 
a  certain  equilibrium  of  temperature  is  thus  established  for  the  body  as 
a  whole.  In  the  observations  of  Jiirgensen,  this  standard  temperature, 
as  measured  in  the  rectum,  was  found  to  vary,  within  narrow  limits, 
from  day  to  night,  and  even  at  successive  periods  in  the  twenty-four 
hours.  These  fluctuations  are  no  doubt  due  to  the  varying  functional 
activity  of  different  parts;  the  total  amount  of  heat  produced  being 
increased  or  diminished  with  the  preponderating  influence  of  organs 
in  which  it  is  more  or  less  rapidly  generated. 

Regulation  of  the  Animal  Temperature. 

A  certain  temperature  is  not  only  the  result  of  the  vital  actions ;  it 
is  also  necessary  to  their  accomplishment.  Even  in  vegetables  this 
temperature,  which  varies  within  moderate  limits  in  different  plants,  is 
requisite  for  all  the  phenomena  of  growth  and  vitality.  A  seed  sown 
in  the  most  productive  soil  does  not  germinate  except  under  the  influ- 
ence of  the  necessary  warmth  ;  and  its  germination  is  also  impossible 
if  it  be  exposed  to  a  heat  which  is  too  intense.  The  degrees  both  of 
heat  and  cold  which  favor  or  arrest  the  functions  of  vegetation  have 
been  in  many  instances  accurately  determined.  According  to  Sachs, 
the  limits  of  germination  for  wheat  and  barley  are  between  5°  and  38° 
C.,  and  for  Indian  corn  between  9°  and  42°.  The  irritability  and 
periodic  movements  of  the  sensitive-plant  do  not  show  themselves 
onksB  the  temperature  of  the  surrounding  air  be  above  15°.  In  air 
at  48°  to  50°,  on  the  other  hand,  the  leaflets  become  rigid  in  a  few 
moments,  though  they  may  afterward  recover  if  the  temperature  be 
moderated;  while  a  heat  of  52°  permanently  destroys  their  vitality. 
Thus  no  vegetative  function  can  come  into  activity,  unless  the  temper- 


ANIMAL    HEAT.  269 

ature  of  the  plant  reaches  a  certain  degree  above  freezing ;  and  it  ceases 
at  another  determinate  temperature,  which  cannot  for  any  considerable 
time  exceed  50°.  Within  these  two  limits  every  vegetable  function  has 
a  special  temperature  at  which  it  is  most  active ;  diminishing  in  inten- 
sity both  above  and  below  this  point. 

The  same  is  true  of  the  animal  functions.  Each  species  of  animal 
has  a  definite  bodily  temperature,  which  cannot  be  raised  or  lowered 
beyond  certain  limits  without  injury.  Mammalians,  whose  normal 
temperature  is  from  31°  to  40°,  become  insensible  and  soon  die,  when 
cooled  down  to  18°  or  20°,  which  is  the  natural  standard  for  reptiles  and 
fish ;  while  a  frog  is  killed  by  being  kept  in  water  at  38°.  On  the  other 
hand,  mammalians  die  when  their  blood  and  internal  organs  are  heated 
up  to  45°,  which  is  precisely  the  normal  temperature  of  birds ;  and 
birds  are  fatally  affected  when  their  temperature  is  raised  to  48°  or  50°. 
In  every  case  the  vital  functions  are  seriously  disturbed  by  a  very  mod- 
erate change  in  the  temperature  of  the  bodily  organs ;  and  in  the  mam- 
malians, as  a  rule,  death  follows  when  this  change  amounts  to  an 
elevation  of  6°  or  7°,  or  to  a  depression  of  20°. 

In  man,  in  febrile  affections,  the  rise  of  temperature,  as  measured  in 
the  axilla,  yields  a  very  accurate  criterion  of  the  gravity  of  the  disease. 
An  increase  of  this  temperature  from  36.6°  to  31.5°  or  38°  C.  indicates 
a  mild  form  of  the  malady ;  but  an  increase  to  40°  or  40.5°  shows  that 
the  attack  is  severe.  Above  40.5°  it  is  a  symptom  of  great  danger; 
and  when  it  rises  to  42.5°  or  43°  a  fatal  result  is  almost  inevitable.* 

Effects  of  Lowering  the  Temperature  of  the  Animal  Body. — If  a 
warm-blooded  animal  or  man  be  exposed  to  cold  in  such  a  way  that  the 
internal  heat  is  abstracted  faster  than  it  can  be  produced,  the  effect  is  a 
general  depression  of  the  vital  functions.  After  a  short  period  of  pain 
in  the  more  exposed  parts,  the  skin  becomes  insensible,  the  muscles 
lose  their  energy,  the  movements  of  respiration  diminish  in  frequency, 
and  the  nervous  system  becomes  inactive.  In  man  a  marked  sluggish- 
ness of  mind,  and  a  disposition  to  sleep  have  been  observed  as  among 
the  symptoms  of  continued  exposure  to  unusually  low  temperatures. 

The  general  effects  of  a  low  temperature  result  from  its  combined 
influence  on  all  the  organs  and  tissues.  According  to  Bernard,  if 
a  rabbit  or  guinea-pig  be  subjected  to  continuous  abstraction  of  heat, 
the  temperature  of  the  animal,  as  taken  in  the  rectum,  gradually  falls 
from  38°  to  30°,  25°,  20°,  and  18°.  When  the  depression  has  reached 
this  point,  there  is  general  insensibility  and  paralysis,  with  feeble  and 
infrequent  respiration.  The  heat-producing  power  is  also  lost,  so  that 
if  the  animal  be  withdrawn  from  the  apparatus,  and  kept  in  the  air  at 
10°  or  12°,  its  temperature,  nevertheless,  continues  to  diminish,  and 
death  takes  place  after  a  short  time. 

But  when  in  this  condition,  although  most  of  the  vital  actions  are 
suspended,  and  the  animal  has  lost  the  power  of  maintaining  his  own 


Flint,  Principles  and  Practice  of  Medicine.    Philadelphia,  1868,  p.  109. 


270  FUNCTIONS    OF    NUTRITION. 

temperature,  if  he  be  supplied  with  artificial  warmth  up  to  a  certain 
point,  he  may  regain  his  vitality,  and  the  processes  of  life  be  again  put 
in  operation.  The  respiration,  which  had  been  reduced  to  a  minimum 
by  the  action  of  cold,  gains  in  rapidity  as  the  body  is  artificially 
warmed,  and  the  functions  of  the  nervous  and  muscular  systems  are 
finally  restored. 

A  striking  example  of  temporary  suspension  of  the  bodily  functions 
by  cold  is  presented  by  the  hibernating  animals,  which  pass  into  a  con- 
dition of  torpor  during  the  winter,  becoming  insensible,  unconscious, 
and  motionless,  while  respiration  is  nearly  imperceptible,  and  the  bodily 
temperature  sinks  to  10°,  or  even  below  it  Life,  however,  is  not  abol- 
ished, but  only  held  in  abeyance ;  and  with  the  return  of  spring  all  the 
functions  resume  their  activity.  A  hibernating  animal  is  somewhat  in 
the  condition  of  a  seed,  which  remains  in  the  ground  over  winter,  with 
its  vitality  dormant,  and  ready  to  come  into  action  when  supplied  with 
the  requisite  warmth. 

Effects  of  Elevating  the  Temperature  of  the  Animal  Body. — If  the 
temperature  of  the  body  be  raised  above  the  normal  standard,  the 
effects  are  quite  different  from  those  produced  by  cold.  In  the  obser- 
vations of  Bernard,  on  birds  and  mammalians  confined  in  heated  air, 
with  due  ventilation,  the  primary  effects  were  increased  frequency  of 
respiration  with  discomfort  and  agitation ;  and  death  was  usually 
accompanied  with  convulsive  movements,  or  preceded  by  an  audible 
cry.  The  fatal  result  was  more  rapidly  produced  in  birds  than  in 
mammalia.  A  rabbit,  in  air  at  65°,  died  in  twenty  minutes ;  and  a 
bird,  in  air  at  the  same  temperature,  in  four  minutes.  This  difference 
is  probably  due  to  the  greater  activity  of  the  circulation  in  birds,  by 
which  external  heat  is  more  rapidly  transferred  to  the  internal  organs ; 
since  the  same  observer  found  that  when  two  rabbits,  one  living  and 
one  dead,  were  placed  in  air  at  100°,  the  internal  temperature  of  the 
living  animal  became  sensibly  raised  sooner  than  that  of  the  dead  one. 
In  a  medium  of  high  temperature,  therefore,  a  fatal  amount  of  heat 
reaches  the  internal  organs  more  rapidly  by  the  circulation  than  by 
conduction  through  the  solid  tissues. 

After  death  from  exposure  to  too  warm  an  atmosphere,  the  internal 
temperature  is  found  to  be  5°  or  6°  above  the  normal  standard;  the 
heart  is  motionless ;  both  the  muscles  and  the  nerves  are  insensible  to 
galvanism ;  and  cadaveric  rigidity  is  established  writh  unusual  prompt- 
itude. In  many  instances  the  blood  is  found  dark-colored  in  the  arte- 
rial as  well  as  in  the  venous  system;  but  this  is  a  post-mortem 
change,  since  observation  shows  that  the  arterial  blood  continues  red 
during  life,  while  its  oxygen  disappears  and  its  color  darkens  after 
the  stoppage  of  respiration.  A  high  temperature  produces  death  appa- 
rently by  hastening,  in  undue  measure,  thr  <-h«'mirnl  changes  in  the 
tissues  and  fluids,  so  that  their  vitality  is  rapidly  exhausted  and  can 
no  longer  be  maintained  by  the  usual  processes  of  nutrition. 

Resistance  of  the  Body  to  Low  External  Temperatures. — Since  an 


ANIMAL    HEAT.  271 

actual  depression  of  the  temperature  of  the  body  is  followed  by  such 
serious  results,  and  since  its  warmth  is  maintained  during  health  at  the 
normal  standard,  notwithstanding  exposure  to  varying  degrees  of  cold, 
it  is  evident  that  the  living  organism  possesses  the  power  of  increasing 
its  internal  production  of  heat,  to  compensate  for  greater  loss  without. 
It  is  a  matter  of  common  observation,  that  moderate  external  cold,  if 
not  too  long  continued,  produces  a  sense  of  warmth  and  increased 
vigor,  instead  of  depression.  The  atmosphere  of  a  winter's  day,  or  a 
cold  shower-bath,  acts  as  a  stimulant  to  the  vital  processes;  and 
although  the  exposed  parts  of  the  skin  may  be  reduced  below  their 
normal  temperature,  the  body,  as  a  whole,  does  not  experience  a  loss 
of  warmth,  but  maintains  its  natural  condition  of  vitality.  It  is 
certain  that  in  these  circumstances  more  heat  must  be  produced  under 
the  influence  of  external  cold. 

The  mode  in  which  this  result  is  accomplished  has  not  been  deter- 
mined with  precision.  It  is  plain  that  the  nervous  system  has  its 
share  in  the  process,  perhaps  by  directly  stimulating  the  molecular 
changes  which  are  active  in  heat-production.  There  are,  however,  two 
sources  of  heat-supply,  which  evidently  play  an  important  part  in  main- 
taining the  temperature  of  the  body  under  exposure  to  cold. 

The  first  of  these  is  muscular  activity.  It  has  been  shown  that  the 
muscles  produce  a  considerable  quantity  of  heat  in  their  own  tissue,  and 
that  this  quantity  is  increased  by  muscular  contraction.  The  total  pro- 
duction of  heat,  therefore,  for  the  whole  body,  must  be  augmented 
when  the  voluntary  muscles  are  thrown  into  activity.  Experience 
shows  that  this  is,  in  fact,  one  of  the  requisite  conditions  of  resistance 
to  cold.  The  stimulus  of  cool  air  upon  the  skin  excites  the  desire  for 
active  movement,  and  muscular  exercise  produces  a  compensating 
quantity  of  internal  heat.  But  if  the  body  be  exposed  to  even  mod- 
erate winter  weather  without  voluntary  motion,  it  must  either  be 
protected  by  an  unusual  quantity  of  clothing,  or  it  will  soon  feel  a 
depressing  effect  from  the  loss  of  its  animal  heat. 

Secondly,  an  increased  production  of  warmth  is  provided  for  by 
increased  supply  of  food.  The  requisite  materials  for  beat-produc- 
tion, in  the  substance  of  the  tissues,  are  primarily  derived  from  the 
ingredients  of  the  food.  Even  a  recent  ingestion  of  food,  as  shown 
by  Senator,  increases  perceptibly,  in  the  dog,  the  amount  of  heat 
generated  within  a  given  time ;  and  for  longer  periods,  the  influence 
of  an  ample  or  a  scanty  supply  is  abundantly  manifest.  In  animals 
which  are  insufficiently  fed  or  ill-nourished,  the  capacity  for  resistance 
to  cold  is  much  less  than  in  those  which  are  in  good  condition  and 
which  have  received  a  fair  quantity  of  food.  The  effect  of  moderate 
exposure  to  cold  in  the  healthy  condition,  is  to  increase  the  appetite. 
A  larger  quantity  of  food  is  habitually  taken  during  the  winter  than 
in  summer ;  and  among  the  inhabitants  of  northern  and  arctic  re- 
gions, the  daily  consumption  is  greater  than  in  temperate  and  tropical 
climates. 


272  FUNCTIONS    OF    NUTRITION. 

It  is  not  necessary  to  assume  that  the  food,  thus  required  for  heat- 
production,  furnishes  directly  the  necessary  warmth  by  its  consump- 
tion. The  heat  is  no  doubt  generated  from  the  nutritive  changes  in 
the  bodily  tissues,  and  these  changes  are  continued  only  by  a  supply  of 
food  sufficient  to  provide  for  the  demands  of  the  system. 

Resistance  of  the  Living  Body  to  High  External  Temperatures. — 
It  has  been  seen  that,  in  man  and  warm-blooded  animals  generally, 
a  rise  in  the  bodily  temperature  of  6°  or  7°  is  certainly  fatal ;  and  yet 
the  body  may  be  exposed,  as  shown  by  repeated  observations,  to  much 
higher  degrees  of  heat  without  injurious  result.  According  to  Car- 
penter,* the  temperature  of  the  air,  in  many  parts  of  the  tropical  zone, 
rises  daily,  through  a  large  portion  of  the  year,  to  43°  C.  In  southern 
Arizona,  the  temperature  at  midsummer,  as  observed  by  Pumpelly,f 
ranges,  in  the  shade,  from  47°  to  52° ;  and  it  is  well  known  that  the 
air  of  manufactory  drying-rooms  and  of  the  Turkish  bath  may  easily 
be  endured  when  considerably  above  45°.  Either  of  these  tempera- 
tures would  be  fatal  to  man,  if  they  indicated  the  actual  warmth  of 
the  internal  organs.  The  body  therefore  must  either  possess  some 
means  of  diminishing  its  own  heat-production,  or  else  of  compensating, 
to  a  certain  extent,  external  temperatures  which  are  above  the  normal 
standard. 

The  most  direct  means  of  moderating  the  temperature  of  the  body  is 
the  cutaneous  perspiration.  This  secretion,  derived  from  the  perspi- 
ratory glands  of  the  skin,  is  clear,  colorless,  and  watery,  with  an  acid 
reaction,  and  a  specific  gravity  of  1003  or  1004. 

It  is  a  fluid  of  very  simple  composition,  containing  over  99^  per 
cent,  of  water,  and  more  than  half  its  solid  ingredients  consisting  of 
inorganic  salts.  There  are  also  traces  of  an  organic  substance  similar 
to  albumen,  and  a  free  volatile  acid,  which  gives  to  the  secretion  its 
reaction  and  odor. 

The  perspiration  is  a  continuous  secretion.  In  a  condition  of  repose 
or  moderate  bodily  activity,  it  is  exuded  so  gradually  that  it  is  at  once 
carried  off  by  evaporation,  and  has  received  the  name,  under  these 
circumstances,  of  the  insensible  transpiration.  The  quantity  of  fluid 
discharged  in  this  way,  according  to  Lavoisier  and  Seguin,  amounts 
on  the  average  to  900  grammes  per  day.  In  addition  to  this,  about 
500  grammes  are  discharged  from  the  lungs,  making  1400  grammes 
of  daily  exhalation  from  the  whole  body.  The  vaporization  of  this 
quantity  of  water  wTill  consume  750  heat  units ;  or  about  one-fifth  of 
all  the  heat  produced  in  the  body  during  twenty-four  hours. 

The  cutaneous  perspiration  may  be  increased  by  temporary  causes. 
An  elevated  external  temperature  or  unusual  muscular  exertion,  will 
accelerate  the  circulation  through  the  skin,  and  largely  augment  the 
amount  of  fluid  discharged.  It  may  then  exude  more  rapidly  than 

*  Principles  of  Human  Physiology.     London,  1869,  p.  483. 
f  Across  Aiiu-rk-a  :md  Asia.     New  York,  1871,  pp.  41,  57,  59. 


ANIMAL    UK  AT.  273 

it  can  be  carried  off  by  evaporation,  collecting-  upon  the  skin  as  a  visible 
moisture,  when  it  is  known  as  the  sensible  perspiration.  The  amount 
discharged  during  violent  exercise  has  been  known  to  rise  as  high  as 
380  grammes  per  hour;  and  Southwood  Smith*  found  that  laborers 
in  heated  gas-works  sometimes  lost,  by  both  cutaneous  and  pulmo- 
nary exhalation,  nearly  1600  grammes  in  the  same  time.  The  evapo- 
ration of  this  increased  quantity  of  fluid  neutralizes  the  effect  of  the 
heated  atmosphere,  and  thus  prevents  an  undue  rise  of  the  bodily  tem- 
perature. 

It  is  possible  that  certain  influences  transmitted  through  the  nerves 
may  also  have  the  power  of  controlling  directly  the  molecular  activity 
of  the  tissues,  and  may  thus  diminish  the  amount  of  internal  heat  at 
the  source  of  its  production ;  but  the  experimental  evidence  of  this 
action  is  yet  incomplete,  and  its  mode  of  operation  comparatively 
obscure. 

The  production  of  animal  heat,  and  the  regulation  of  the  bodily 
temperature,  by  which  it  is  maintained  at  or  near  a  normal  standard, 
are  two  of  the  most  important  phenomena  presented  by  the  living 
organism.  They  result  from  an  associated  series  of  vital  actions,  and 
are  at  the  same  time  essential  conditions  for  the  continuance  of  life. 


*  Philosophy  of  Health.    London,  1838,  chap.  xiii. 

S 


CHAPTER    VI. 
THE    CIRCULATION. 

THE  circulatory  system  is  an  apparatus  by  which  the  blood  is  trans- 
ported to  different  regions  of  the  body,  and  by  which,  after  serving 
for  nutrition,  absorption,  or  secretion,  it  is  returned  to  the  lungs  for 
aeration.  By  this  movement  of  the  blood  in  a  continuous  circuit,  the 
materials  absorbed  in  the  alimentary  canal  are  conveyed  to  distant 
parts  for  their  nourishment  and  growth,  the  oxygen  taken  in  by  the 
lungs  is  distributed  throughout  the  body,  the  products  of  excretion 
find  their  way  to  the  outlets  of  the  system,  and  the  losses  by  exhala- 
tion in  one  organ  are  made  good  by  absorption  in  another.  The  me- 
chanical function  by  which  this  is  accomplished  is  regulated  by  the 
conditions  of  compression,  fluidity,  and  resistance,  under  which  the 
blood  moves  through  the  blood-vessels. 

The  circulatory  apparatus  consists  of  four  different  parts,  namely, 
1st.  The  heart,  a  hollow,  muscular  organ,  which  propels  the  blood. 
2d.  The  arteries,  a  series  of  branching  tubes,  which  convey  it  to  dif- 
ferent parts  of  the  body.  3d.  The  capillaries,  a  network  of  inosculating 
tubules,  interwoven  with  the  substance  of  the  tissues,  bringing  the 
blood  into  intimate  relation  with  their  component  parts ;  and  4th.  The 
veins,  a  system  of  converging  vessels,  which  collect  the  blood  from  the 
capillaries,  and  return  it  to  the  heart.  In  each  of  these  different  parts 
of  the  circulatory  apparatus,  the  movement  of  the  blood  is  dependent 
on  special  conditions. 

The  Heart. 

The  structure  of  the  heart  and  its  relation  with  the  adjacent  vessels, 
is  particularly  connected  with  the  activity  and  mechanism  of  respira- 
tion. In  man  and  mammalians,  this  function  is  very  active,  and  is 
performed  almost  exclusively  by  the  lungs.  The  whole  of  the  blood, 
accordingly,  after  returning  from  the  periphery,  passes  through  the 
lungs  before  it  is  again  distributed  to  the  system  at  large.  It  thus 
traverses  in  succession  the  general  circulation  for  the  whole  body,  and 
the  special  circulation  of  the  lungs.  The  mammalian  heart  (Fig.  57), 
consists  of  a  right  auricle  and  ventricle  (a,  6),  receiving  the  blood  from 
the  vena  cava  (i),  and  driving  it  to  the  lungs;  and  a  left  auricle  and 
ventricle  (/,  g)  receiving  the  blood  from  the  lungs  and  propelling  it 
outward  through  the  arterial  system. 

It  is,  therefore,  a  double  organ,  with  two  sets  of  muscular  cavities, 
right  and  left;  its  right  cavities  being  devoted  to  the  circulation 

274 


THE    CIRCULATION. 


275 


FIG.  57. 


through  the  lungs,  its  left  cavities  to  that  through  the  general  system. 

It  is  of  a  somewhat  conical  form  ; 

its  base,  situated  upon  the  me- 

dian line,  being  directed  upward 

and  backward,  while  its  apex,  in 

man,  points  downward,  forward, 

and  to  the  left,  surrounded  by 

the  pericardium,  but  capable  of 

a  certain  degree  of  lateral  and 

rotatory  motion.     The  auricles, 

which  have  a  smaller  capacity 

and  thinner  walls  than  the  ven- 

tricles, are  situated  at  its  upper 

and   posterior   part,   while   the 

ventricles    occupy   its    anterior 

and  lower  portions.     The  two 

ventricles,  moreover,  are  upon 

different  planes.    The  right  ven- 

tricle is  somewhat  in  front  and 

above  the  left  ;    so  ^that  in  an 

anterior  view  the  greater  por- 

tion of  the  left  ventricle  is  con- 

cealed by  the  right,  and  in  a 

posterior  view  the  greater  por- 

tion of  the  right  ventricle  is  concealed  by  the  left  ;    while  in   both 

positions  the  apex  of  the  heart  is  constituted  altogether  by  the  point 

of  the  left  ventricle. 

The  cavities  of  the  heart  and 
of  the  adjacent  blood-vessels  on 
each  side,  though  continuous 
with  each  other,  are  partially 
separated  by  certain  construc- 
tions, The  orifices  by  which 
they  communicate  are  known 
by  the  names  of  the  auricular, 
auriculo-ventricular,  and  aortic 
and  pulmonary  orifices  ;  the 
auricular  orifices  being  the  pas- 
sages from  the  venae  cavaB  and 
pulmonary  veins  into  the  right 
and  left  auricles  ;  the  auriculo- 
ventricular  orifices  leading  from 
the  auricles  into  the  ventricles  ; 


DIAGRAM  OF  THE  HEART  AND  PULMONARY  CIR- 
CULATION IN  MAMMALIANS.— a.  Right  auricle. 
b.  Right  ventricle,  c.  Pulmonary  artery,  d. 
Lungs,  e.  Pulmonary  vein.  /.  Left  auricle,  g. 
Left  ventricle,  h.  Aorta,  i.  Vena  cava. 


FIG.  58. 


orifices   leading   from  the  ven- 
tricles into  the  aorta  and  pulmonary  artery  respectively. 

The   auriculo-ventricular,  aortic,   and    pulmonary  orifices  are   fur- 


276 


FUNCTIONS    OF    NUTRITION. 


FK;.  oil. 


nished  with  valves,  which  allow  the  blood  to  pass  from  the  auricles 

to  the  ventricles,  and  from  the 
ventricles  to  the  arteries,  but 
close  against  its  return  in  the 
opposite  direction.  The  course 
of  the  blood  through  the  heart 
is,  therefore,  as  follows.  Froan 
the  vena  cava  it  passes  into 
the  right  auricle ;  and  from 
the  right  auricle  into  the  right 
ventricle.  On  the  contraction 
of  the  right  ventricle,  the  tri- 
cuspid  valves  shut  back,  pre- 
venting its  return  into  the 
auricle  (Fig.  59) ;  and  it  is 
driven  through  the  pulmonary 
artery  to  the  lungs.  Returning 
from  the  lungs,  it  enters  the  left 
auricle,  thence  passes  into  the 


RIGHT  CAVITIES  OF  THE  HKAUT;  Auriculo-ventricu 
lar  Valves  closed,  Arterial  Valves  open. 


FIG.  60. 


left  ventricle,  from  which  it  is 
delivered  into  the  aorta,  and  distributed  throughout  the  body.  The  two 
streams  of  blood,  arterial  and  venous,  in  their  passage  through  the  heart, 
follow,  in  each  case,  a  curvi- 
linear and  more  or  less  spiral 
direction ;  the  axes  of  the  cur- 
rents crossing  each  other  in  the 
right  and  left  cavities  respect- 
ively (Fig.  60).  The  venous 
blood,  received  by  the  right  au- 
ricle from  the  venae  cavae,  passes 
downward  and  forward  into  the; 
ventricle.  It  there  turns  from 
below  upward,  from  right  to 
left  and  from  before  backward, 
through  the  conus  arteriosus,  to 
the  pulmonary  artery.  On  re- 
turning from  the  lungs  to  the 
left  auricle,  it  passes  downward 
into  the  left  ventricle,  when  it 
makes  a  turn  like  that  upon  the 
right  side,  passing  from  below 
upward  and  from  left  to  right, 
behind  the  conus  arteriosus,  and  crossing  its  axis  at  an  acute  angle,  to  the 
commencement  of  the  aorta.  The  aorta,  though  at  its  origin  somewhat 
posterior  to  the  pulmonary  artery,  soon  comes  to  the  front  in  its  arched 
portion,  while  the  pulmonary  artery  runs  almost  directly  backward.  Thus 
the  two  blood-currents  twist  spirally  round  each  other  in  their  course. 


COUBSE  <>K  P.i.ooi)  iiiKori.n  Tin.  HKAIIT.—  <i,  <i. 
Vrna  cava,  superior  and  inl'iTim1.  /'.  Ki^lit  v«-n- 
triclc.  r.  Pulmonary  artery,  d.  Pulmonary  vein. 
e.  Left  ventricle.  /.  Aorta. 


THE    CIRCULATION.  277 

The  passage  of  the  blood  through  the  heart  is  accomplished  by 
alternate  contraction  and  relaxation  of  its  muscular  walls ;  by  which 
successive  portions  are  delivered  from  the  auricles  into  the  ventricles, 
and  thence  into  the  arteries.  Each  movement  of  this  kind  is  called  a 
beat  or  pulsation  of  the  heart.  The  cardiac  pulsations  are  accompanied 
by  certain  phenomena  dependent  on  the  structure  of  the  organ  and  its 
mode  of  action. 

Sounds,  Movements,  and  Impulse  of  the  Heart. — The  sounds  of  the 
heart  are  two  in  number,  differing  from  each  other  in  time,  tone,  and 
duration.  They  are  known  as  the  first  and  second  sounds,  and  may 
be  heard  on  applying  the  ear  to  the  chest  at  the  cardiac  region.  The 
first  sound  is  loudest  over  the  anterior  surface  of  the  heart,  particularly 
at  the  situation  of  the  apex  beat,  over  the  fifth  rib  and  fifth  intercostal 
space.  It  is  comparatively  long  and  dull  in  tone,  and  occupies  one-half 
the  duration  of  a  beat.  It  corresponds  in  time  with  the  impulse  of  the 
heart  in  the  precordial  region,  and  with  the  stroke  of  the  large  arteries 
in  the  vicinity  of  the  chest.  The  second  sound  follows  almost  immedi- 
ately upon  the  first.  It  is  most  audible  at  the  situation  of  the  aortic 
and  pulmonary  valves,  namely,  over  the  sternum  at  the  level  of  the 
third  costal  cartilage.  It  is  short  and  distinct,  and  occupies  about  one- 
quarter  of  the  time  of  a  pulsation.  It  is  followed  by  an  equal  interval 
of  silence ;  after  which  the  first  sound  recurs.  The  whole  time  of  a 
pulsation  may  be  divided  into  four  quarters,  of  which  the  first  two  are 
occupied  by  the  first  sound,  the  third  by  the  second  sound,  and  the 
fourth  by  an  interval  of  silence,  as  follows : 

TIME  AND  DURATION  OF  THE  HEART-SOUNDS. 

f  ^  1ua^terl  First  sound. 
Cardiac  pulsation        £  gecond  gound 

1  4th       "          Interval  of  silence. 

The  first  sound  of  the  heart  is  mainly  produced  by  the  tension  and 
consequent  vibration  of  the  auriculo-ventricular  valves  and  chords 
tendineae  at  the  time  of  ventricular  systole.  It  may  be  imitated  by 
alternately  loosening  and  extending  a  tape  or  ribbon,  with  its  ends 
firmly  held  between  the  fingers  of  the  two  hands.  According  to  Chau- 
veau  and  Faivre,*  when  the  tension  of  the  auriculo-ventricular  valves 
is  prevented,  in  the  horse,  either  by  dividing  the  chords  tendinese,  or 
by  inserting  into  the  auriculo-ventricular  orifice  a  short  tube,  from  1J- 
to  2  centimetres  in  diameter,  the  sound  is  changed  in  character,  and 
replaced  by  a  soft  murmur ;  a  reflux  of  blood,  at  the  same  time,  taking 
place  into  the  auricle.  Valvular  tension  is  therefore  generally  admitted, 
as  a  cause  for  the  first  sound,  and  by  many  observers  is  regarded  as 
fully  sufficient  to  account  for  it.  There  is  a  difference  of  opinion  as  to 

*  Dictionnaire  Encyclopedique  des  Sciences  Medicales.  Paris,  1876,  tome  xviii., 
p.  344. 


278  FUNCTIONS    OF    NUTRITION. 

the  admixture  of  another  element  in  its  production,  namely,  the  muscu- 
lar contraction  of  the  ventricular  walls.  But  from  the  evidence  thus 
far  presented,  it  appears  that  the  direct  share  of  muscular  contraction 
in  the  first  sound,  if  it  exist  at  all,  must  be  secondary  in  importance  to 
that  of  valvular  tension. 

The  cause  of  the  second  sound  is  universally  acknowledged  to  bo  the 
sudden  closure  and  tension  of  the  aortic  and  pulmonary  valves,  under 
the  reaction  of  arterial  pressure  at  the  end  of  the  ventricular  systole. 
These  valves  are  fibrous,  semilunar  festoons,  which  yield  to  the  current 
of  blood  passing  from  the  ventricle  into  the  artery  (Fig.  59),  and  which 
shut  together  in  the  form  of  distended  sacs  (Fig.  58)  when  the  artery 
reacts  upon  its  contents.  Their  connection  with  the  second  sound 
of  the  heart,  which  occurs  at  the  same  time,  is  established  by  the 
following  proofs:  1st.  The  sound  is  heard  with  complete  distinct- 
ness directly  over  the  situation  of  these  valves  at  the  base  of  the 
heart;  2d.  The  farther  we  recede  in  any  direction  from  this  point, 
the  fainter  it  becomes;  and  3d.  All  experimenters  agree  that  when 
the  semilunar  valves  are  hooked  back  against  the  inner  surface  of  the 
artery  by  curved  needles,  or  held  open  by  fine  springs  introduced  into 
the  vessel,  the  second  sound  disappears,  and  remains  absent  until  the 
valves  are  again  liberated. 

The  difference  in  character  between  the  first  and  second  sounds  of  the 
heart  is  apparently  due  to  the  difference  in  size  and  attachment  of  the 
auriculo-vcntricular  and  the  semilunar  valves.  The  former  are  com- 
paratively broad  sheets  attached  by  their  external  edges  to  the  auriculo- 
ventricular  fibrous  zones,  and  by  their  internal  edges  and  lower  sur- 
faces, through  the  chordae  tendinese,  to  the  musculi  papillares  of  the 
ventricular  walls.  The  latter  are  of  smaller  size,  and  attached  only  to 
the  fibrous  zones  at  the  base  of  the  large  arteries.  In  imitating  the 
effect  of  valvular  tension  with  a  piece  of  ribbon  or  other  woven  fabric, 
a  longer  piece  will  yield  a  sound  similar  to  the  first  sound  of  the  heart, 
a  shorter  piece  one  similar  to  the  second  sound. 

The  movements  of  the  heart  may  be  observed  in  the  dog,  or  other 
warm-blooded  quadruped,  after  opening  the  chest  by  a  longitudinal 
incision  through  the  sternum  and  separating  the  costal  cartilages  on 
each  side  at  their  junction  with  the  ribs;  artificial  respiration  beinir 
maintained  by  the  nozzle  of  a  bellows  inserted  into  the  trachea.  The 
animal  may  be  etherized  and  rendered  permanently  insensible  by  tre- 
phining the  skull,  and  applying  cerebral  compression,  or  he  may  be  par- 
tially narcotized  by  a  preliminary  subcutaneous  injection  of  morphine, 
sifter  which  etherization  is  produced,  and  continued  with  great  facility. 
The  operation  of  opening  the  chest-  and  exposing  the  thoracic  organs 
increases  the  rapidity  of  the  heart's  movements,  and  diminishes  their 
force  ;  but  they  often  have  sufficient  vigor  to  continue  with  regularity 
for  one  or  two  hours,  if  artificial  respiration  be  properly  maintained. 

When  exposed  to  view  by  this  means,  the  action  of  the  heart  is  so 
complicated  that  it  requires  a  close  examination  to  appreciate  its  char- 


THE    CIRCULATION,  279 

acter.  It  is  obvious  at  the  outset  that  the  organ  presents  itself  in 
two  different  conditions,  alternating  with  each  other  in  rapid  suc- 
cession ;  namely,  a  condition  of  rest  and  a  condition  of  movement. 
One  of  these  is  the  condition  in  which  it  expels  the  blood  from 
the  ventricles  into  the  arteries ;  the  other  is  that  in  which  the  ventri- 
cles are  again  filled  with  blood  from  behind.  The  first  object  of  the 
observer  is  to  determine  the  time  at  which  each  one  of  these  two  con- 
ditions presents  itself,  and  the  physical  changes  in  the  organ  by  which 
it  is  accompanied.  If  the  heart  be  touched  or  gently  grasped  by  the 
fingers,  its  alternations  of  rest  and  movement  are  felt  to  correspond  with 
similar  variations  in  its  consistency.  At  the  time  of  rest  it  is  compar- 
atively soft  and  yielding ;  at  the  time  of  its  movement  it  becomes  hard 
and  tense.  If  a  slender  silver  canula  be  inserted,  through  the  walls  of 
the  left  ventricle,  into  its  cavity,  the  blood  is  ejected  from  the  outer 
extremity  of  the  canula  at  the  instant  of  the  heart's  tension  and  move- 
ment, while  its  flow  is  suspended  in  the  intervals  of  repose. 

It  is  evident,  therefore,  that  the  time  of  the  heart's  movement  is  that 
of  the  ventricular  systole,  in  which  the  muscular  walls  of  the  ventricles 
close  upon  their  contents,  and  propel  the  blood  into  the  arterial  sys- 
tem. Like  other  muscles,  the  heart  assumes,  at  the  instant  of  contrac- 
tion, a  condition  of  rigidity,  readily  perceptible  on  placing  the  fingers 
in  contact  with  its  surface. 

If  the  muscular  fibres  of  the  heart  ran  in  a  straight  direction  be- 
tween their  points  of  origin  and  insertion,  its  changes  of  form  and 
position,  like  those  of  most  voluntary  muscles,  would  be  compara- 
tively simple.  But  they  are  in  the  form  of  elongated  curvilinear  loops, 
which  have  their  origin  in  the  fibrous  zones  at  the  base  of  the  organ, 
and,  after  embracing  the  ventricular  cavities,  return  to  be  inserted  into 
the  same  fibrous  zones  or  into  the  chordae  tendineae.  As  the  entire 
heart,  furthermore,  is  attached  at  its  base,  while  its  body  and  apex  are 
movable,  the  united  action  of  its  fibres  produces  a  combination  of 
simultaneous  movements  different  from  those  of  other  muscular  organs. 

In  an  anterior  view  of  the  dog's  heart,  the  base  of  the  organ,  at 
each  ventricular  systole,  appears  to  approach  its  apex.  The  point  of 
the  heart  is  at  the  same  time  protruded,  tilted  slightly  from  left  to 
right,  and  rotated  in  the  same  direction  on  its  longitudinal  axis. 
The  protrusion  of  the  apex  can  be  felt  somewhat  forcibly  by  the  end 
of  the  finger  applied  lightly  to  its  surface,  and  it  can  also  be  shown  by 
the  movement  of  a  long  steel  needle  suspended  vertically  on  a  hori- 
zontal axis,  so  that  its  lower  extremity  touches  the  point  of  the  heart, 
At  each  cardiac  systole,  the  upper  end  of  the  needle  moves  backward, 
as  its  lower  end  is  thrown  forward  by  the  protrusion  of  the  apex. 
At  the  same  time,  the  body  of  the  organ  is  increased  in  thickness  from 
its  anterior  to  its  posterior  surface,  and  diminished  in  its  transverse 
diameter,  that  is,  from  the  right  to  the  left  lateral  border.  All  these 
phenomena  depend  on  the  anatomical  arrangement  of  the  contracting 
fibres. 


280  FUNCTIONS    OF    NUTRITION. 

The  descent  of  the  base  of  the  heart  in  front  toward  its  apex  is 
due  to  the  contraction  of  the  right  ventricle,  which  occupies  most  of 
the  anterior  surface  of  the  organ,  being  wrapped  round  the  left  ven- 
tricle from  below  upward  and  from  right  to  left,  and  continuing  its 
course  in  this  direction,  as  the  conus  arteriosus,  to  the  base  of  the  pul- 
monary artery.  Its  superficial  muscular  fibres  run  obliquely  from  above 
downward  and  from  right  to  left,  uniting  with  those  of  the  left  ven- 
tricle at  the  inter  ventricular  sulcus.  The  base  of  the  heart  in  an  ante- 
rior view  is  therefore  the  upper  border  of  the  right  ventricle  and  conus 
arteriosus;  and  it  is  brought  downward,  by  the  contraction  of  the 
descending  muscular  fibres,  toward  the  inter  ventricular  sulcus  and  the 
point  of  the  heart.  The  principal  part  of  the  cardiac  mass,  in  warm- 
blooded quadrupeds,  consists  of  the  left  ventricle ;  while  the  right 
ventricle  is  an  additional  chamber  or  covered  passage-way,  leading  to 
the  pulmonary  artery,  very  visible  in  a  front  view,  owing  to  its  situa- 
tion, but  forming  a  small  portion  of  the  substance  of  the  organ.  The 
relative  volume  of  the  two  ventricles  may  be  shown  by  a  trans  verse- 
section  of  the  heart  in  its  contracted  condition.  The  left  ventricle 
forms  a  thick  muscular  cone,  with  its  cavity  nearly  in  the  centre  of 

the  cardiac  mass;  while  the  right 
ventricle  is  a  comparatively  inconsid- 
erable layer  of  fibres  attached  to  tin- 
surface  of  the  organ  and  enclosing 
a  cavity  of  more  linear  and  flattened 
form.  Its  contraction,  accordingly, 
may  produce  a  marked  change  in  the 
superficial  aspect  of  the  heart,  with- 
out causing  an  important  alteration 
in  its  entire  form. 

TRANSVERSE  SECTION  OF  THE  BULLOCK'S 

UK  ART  IN  THE  STATE  OF  CADAVERIC  RIG-         The  deviation  of  the  heart's  apex 

iDiTY.-a.  Cavity  of  the  Left  Ventricle.       toward    the    right,  and    itS    axial  rota- 
te'avity  of  the  Right  Ventricle.  ' 

tion  in  the  same  direction,  at  the  ven- 

irieular  systole,  are  caused  by  the  obliquity  of  the  external  cardiac 
fibres,  and  the  mode  of  their  penetration  at  the  apex.  The  most 
Mijierlicial  of  these  fibres,  running  obliquely  from  above  downward 
and  from  right  to  left,  at  the  time  of  their  contraction  tilt  the  point 
of  the  heart  slightly  toward  the  right.  Near  the  apex  of  the  organ 
they  curl  round  its  axis,  and  suddenly  change  their  direction,  passing 
into  the  interior  of  the  ventricles  as  deep-seated  til  ires,  and  thence 
running  upward,  to  terminate  in  the  chorda-  tendinea*  and  auriculo- 
ventricular  zones. 

They  thus  form,  exactly  at  the  point  of  the  heart,  a  whorl  or  vortex 
of  converging  fibres.  Muscular  fibres,  arranged  in  this  way,  necessarily 
tend,  in  contracting,  to  straighten  themselves  and  untwist  the  spiral. 
At  the  ventricular  systole,  therefore,  the  heart  rotates  on  its  axis,  from 
left  to  right  anteriorly,  and  from  right  to  left  posteriorly.  This  pro- 
duces the  twisting  movement  perceptible  at  the  apex. 


THE    CIRCULATION. 


281 


The  protrusion  of  the  point  of  the  heart   in   contraction  has  been 
variously  regarded ;  first  as  an  elongation  of  the  cone  formed  by  the 

FIG.  62. 


f 


FIG.  63. 


BULLOCK'S    HEART,    anterior    view,       CONVERGING  SPIRAL  FIBRES  AT  THE   APEX   OP  THE 
showing    the    superficial   muscular  HEART.— The  direction  of  the  arrows  indicates  that  of 

fibres.  the  rotating  movement  of  the  heart  at  the  ventricular 

systole. 

left  ventricle,  and  secondly,  as  a  movement  of  the  whole  heart,  due  to  a 
recoil  from  the  blood  expelled  from  it  under  pressure,  or  to  a  reaction 
of  the  distended  arteries  at  its  base.  Many  of  the  earlier  observers 
(Galen,  Yesalius,  Harvey,  Riolanus,  Borelli,  Winslow)  found  the  longi- 
tudinal diameter  of  the  heart  increased  at  the  moment  of  systole,  and 
its  transverse  diameter  diminished.  Pennock  and  Moore,*  in  1839,  in 
a  series  of  experiments  on  sheep,  calves,  and  horses,  also  observed  an 
elongation,  the  extent  of  which  they  measured  with  a  graduated  rule. 
On  the  other  hand  some  of  the  earlier,  and  nearly  all  the  more  recent 
writers  of  eminence  (Lower,  Haller,  Longet,  Carpenter,  Flint,  Ranke, 
Chauveau,  Burdon-Sanderson)  are  of  opinion  that  the  heart  shortens 
during  systole,  being  diminished  in  both  its  longitudinal  and  trans- 
verse diameters.  In  our  own  observations  we  have  always  seen  reason 
to  admit  that  the  forward  movement-  of  the  apex  is  due  to  an  elonga- 
tion of  the  heart  at  the  moment  of  systole.  This  is  not  easily  percep- 
tible in  a  front  view,  owing  to  the  prominent  action  of  the  right  ven- 
tricle on  the  anterior  surface  of  the  organ.  But  if  the  heart  be  tilted 
upward  and  viewed  from  its  posterior  surface,  formed  mainly  by  the 
left  ventricle,  while  its  base  is  firmly  held  by  the  fingers  placed  upon 
the  great  vessels,  at  every  contraction  its  sides  will  be  seen  to  approxi- 
mate each  other,  and  its  point  to  protrude;  that  is,  its  longitudinal 
diameter  is  increased,  and  its  transverse  diameter  diminished.  The 
end  of  the  finger  in  contact  with  the  apex  is  forcibly  thrown  upward 
by  the  contracting  ventricle,  and  a  light  rider  of  paper  placed  on  the 
*  MedicaTExammer.  Philadelphia,  1839,  No.  44. 


282  FUNCTIONS    OF    NUTRITION. 

point  of  the  heart  is  carried  in  the  same  direction.  If  an  ivory  or 
porcelain  rod  be  held  horizontally  just  above  the  heart  in  this  position, 
the  apex  rises  visibly  toward  the  rod  at  each  ventricular  systole,  and 
recedes  from  it  in  the  same  degree  at  each  diastole. 

Such  an  elongation  can  only  be  explained  by  the  arrangement  of  the 
fibres  in  the  ventricular  wall.  Every  muscular  fibre,  during  contrac- 
tion, increases  in  thickness  while  diminishing  in  length ;  so  that  its 
volume  remains  the  same.  The  superficial  cardiac  fibres  which  run 
obliquely  downward  to  the  point  of  the  heart,  and  then  turn  upward 
along  its  internal  surface  to  their  insertion  in  the  auriculo-ventricular 
zones,  would  have  the  effect,  if  they  acted  alone,  to  draw  the  point  and 
base  of  the  organ  together  and  thus  to  shorten  the  heart.  But  between 
their  superficial  and  internal  layers  there  are  deep-seated  fibres,  running 
in  a  nearly  circular  direction  round  the  axis  of  the  ventricular  cavity. 
These  circular  fibres,  which  are  nearly  wanting  on  the  right  side,  are 
very  abundant  in  the  left  ventricle  and  form  a 
large  part  of  its  muscular  walls.  In  the  ventricu- 
lar systole  they  contract  upon  the  blood  in  the 
ventricular  cavity  like  the  fingers  of  a  closed  hand. 
By  their  contraction  they  tend  to  obliterate  the 
ventricular  cavity,  and  by  their  lateral  swelling 
at  the  same  time  they  exert  a  pressure  from  the 
base  of  the  heart  toward  its  point,  causing  a  pro- 
trusion of  the  apex. 

The  impulse  of  the  heart  is  a  stroke  of  the  apex 
against  the  walls  of  the  chest,  usually  perceptible* 
both  to  sight  and  touch,  at  the  time  of  ventricu- 
LEFT  VENTRICLE  OF  BUL-    iar  sy stole.     In  man  it  is  felt,  as  a  rule,  in  the 

LOCK'S  HEART,  showing     „  „  ,     .    ,  .  , 

its  deep  fibres.  fifth  intercostal  space,  about  midway  between  the 

,  left  edge  of  the  sternum  and  a  vertical  line  drawn 
through  the  left  nipple.  But  its  location  varies  somewhat  with  the 
attitude  and  the  respiration,  owing  to  changes  of  position  of  the  heart 
within  the  chest.  In  the  recumbent  posture,  when  lying  on  the  left 
side,  the  situation  of  the  heart's  impulse  is  shifted  from  one  and  a  half  to 
two  centimetres  farther  outward  from  the  median  line.  When  lying  on 
the  right  side,  it  maybe  altogether  imperceptible.  In  every  posture 
it  disappears  when  the  chest  is  fully  expanded  in  inspiration,  as  the 
cardiac  surface  is  then  completely  covered  by  the  lungs.  But  if  inspira- 
t  inn  lie  performed  by  the  diaphragm  alone,  the  chest  reinaininir  fixed,  the 
descent  of  the  heart,  as  it  follows  the  diaphragm,  is  indicated  by  the 
changed  position  of  the  impulse-.  This  is  most  distinctly  shown  in  the 
recumbent  posture  on  the  left  side;  when,  in  moderate  expiration,  the 
heart's  impulse  is  felt  in  the  fifth  intercostal  space,  but  in  full  inspi- 
ration. usiiiLr  the  diaphragm  alone,  it  disappears  from  that  point  and 
is  felt  in  the  sixth  intercostal  space.  In  the  erect  posture  the  impnl>e 
may  also  be  felt  in  the  sixth  intercostal  space  after  full  inspiration  by 
the  diaphragm  alone. 


THE    CIRCULATION.  283 

The  immediate  cause  of  the  cardiac  impulse  is,  without  question,  the 
shock  of  the  heart  against  the  walls  of  the  chest.  Its  character,  its 
coincidence  in  time  with  the  ventricular  systole,  its  position,  and  its 
variation  with  the  changes  of  attitude  and  respiration,  all  indicate  its 
dependence  on  the  muscular  action  of  the  heart's  apex.  As  to  the 
exact  manner  in  which  it  is  produced  there  is  a  difference  of  opinion. 
By  some  a  large  share  is  attributed  to  the  direct  protrusion  of  the  apex 
and  its  lateral  movement  toward  the  right ;  both  of  which  would  bring 
it  in  contact  with  the  chest  with  sufficient  force  to  lift  the  integuments 
at  the  intercostal  spaces.  Others  regard  it  as  due  to  the  sudden  harden- 
ing of  the  ventricle  at  the  time  of  systole  and  the  slight  increase  in  its 
antero-posterior  thickness  at  the  same  time.  It  is  certain  that  the  heart 
in  contraction  acquires  a  much  firmer  consistency,  and  this  undoubtedly 
adds  to  the  effect  of  the  protrusion  and  movement  of  the  apex,  as  felt 
externally. 

Rhythm  of  the  Heart's  Action. — The  succession  of  phenomena  in  a 
cardiac  pulsation  consists  of  a  double  series  of  contractions  and  relaxa- 
tions ;  namely,  those  of  the  auricles  and  those  of  the  ventricles.  The 
two  auricles  contract  simultaneously  with  each  other,  and  afterward 
the  two  ventricles ;  and  in  each  case  the  contraction  is  followed  by  a 
relaxation.  The  auricular  contraction,  which  is  short  and  compara- 
tively feeble,  occupies  the  first  part  of  the  time  of  a  pulsation.  The 
ventricular  contraction  is  longer  and  more  powerful,  and  occupies  the 
latter  part  of  the  same  period.  Then  comes  a  short  interval  of  repose, 
after  which  the  auricular  contraction  again  recurs.  The  auricular  and 
ventricular  contractions,  however,  are  not  completely  separated  from 
each  other,  like  the  alternate  strokes  of  two  pistons  in  a  forcing-pump, 
but  are  in  some  measure  connected  and  continuous.  The  muscular 
action,  after  beginning  at  the  auricle,  is  at  once  propagated  to  the  ven- 
tricle and  runs  rapidly  toward  the  apex.  The  entire  ventricle  contracts 
vigorously,  its  walls  harden,  its  point  protrudes,  impinges  against  the 
walls  of  the  chest  and  twists  from  left  to  right,  the  auriculo-ventricular 
valves  shut  back,  the  first  sound  is  produced,  and  the  blood  is  driven 
into  the  arterial  system.  These  phenomena  occupy  about  one-half  the 
time  of  pulsation.  Then  the  ventricle  is  relaxed,  and  a  period  of  repose 
ensues.  During  this  period  the  blood  flows  from  the  large  veins  into 
the  auricle,  and  through  the  auriculo-ventricular  orifice  into  the  ventri- 
cle ;  filling  the  ventricle,  by  a  kind  of  passive  dilatation,  about  two- 
thirds  or  three-quarters  full.  Then  the  auricle  contracts  with  a  quick 
motion,  forcing  the  last  drop  of  blood  into  the  ventricle,  and  distending 
it  to  its  full  capacity ;  when  the  ventricular  contraction  again  takes 
place,  driving  the  blood  into  the  large  arteries.  These  movements 
alternate  with  each  other,  and  form,  by  their  recurrence,  the  successive 
cardiac  pulsations. 

The  successive  elements  in  a  cardiac  pulsation,  and  the  corresponding 
variations  of  pressure  in  the  auricular  and  ventricular  cavities,  are  most 
distinctly  shown  by  means  of  the  double  cardiograph,  a  registering 


284 


FUNCTIONS    OF    NUTRITION. 


apparatus,  first  employed  by  Marey.*  The  apparatus  is  composed  of 
two  parts ;  first,  an  instrument  introduced  into  the  cardiac  cavities,  to 
receive  and  transmit  their  variations  of  pressure ;  and  secondly,  a  reg- 
istering machine,  by  which  these  variations  are  permanently  recorded. 

The  first  instrument  consists  of  two  slender  parallel  tubes,  of  such 
length  that,  when  introduced  into  the  jugular  vein  of  the  horse,  one 
will  reach  the  cavity  of  the  right  auricle,  the  other  that  of  the  right 
ventricle.  The  lower  extremity  of  each  tube  is  widely  fenestrated  and 
covered  with  an  elastic  membrane,  to  receive  the  pressure  of  the  blood 
in  the  cardiac  cavity.  The  upper  extremity  is  connected  by  a  flexible 
tube  with  a  shallow  metallic  cup  or  drum,  also  covered  with  an  elastic 
membrane.  By  this  means  the  pressure  of  the  blood  within  the  auricle 
or  ventricle  is  communicated  to  the  corresponding  external  drum.  Upon 
each  drum  rests  a  light  lever,  in  such  a  way  that  any  increased  pressure 
within  the  drum,  which  distends  its  elastic  membrane,  lifts  at  the  same 
time  the  farther  end  of  the  lever.  Consequently  the  oscillation  of  the 
two  levers  indicates  the  variations  of  pressure  within  the  auricle  and 
ventricle  respectively. 

The  registering  machine  consists  of  a  revolving  cylinder  or  strip  of 
paper,  moving  by  clockwork  at  a  uniform  rate,  with  which  the  extremi- 
ties of  the  levers  are  in  contact,  and  upon  which  they  trace  correspond- 

FIG.  65. 


CARDIOGRAPH  10  TRACE,  showing  variations  of  pressure  during  cardiac  pulsations  in  the  right 
auricle  and  right  ventricle  of  the  horse.  R  A.  Tracing  of  right  auricle,  o,  o,  o.  Maximum  of 
pressure  in  auricular  cavity.  R  V.  Tracing  of  right  ventricle,  x,  x,  x.  Maximum  of  pnvMir.- 
in  ventricular  cavity.  (Marey.) 

ing  lines.  When  the  pressure  in  either  cardiac  cavity  is  uniform,  its 
lever  will  trace  upon  the  revolving  cylinder  a  straight  line  ;  but  when- 
ever this  pressure  is  increased  the  line  will  rise  above  the  horizontal, 
and  when  it  is  diminished  the  line  will  sink  to  a  corresponding  level. 
The  upward  and  downward  slopes  of  the  two  tracings  will  therefore 
record  the  time,  rapidity,  force,  and  duration  of  all  changes  in  pressure 
in  tin-  right  auricle  and  right  ventricle  of  the  animal  under  observation. 
The  tracings  obtained  by  this  method  (Fig.  05)  show  that  the  con- 
traction of  the  auricle  precedes  by  a  very  short  interval  that  of  the 

•  Physiologic  M&licale  ck-  l:i  ( 'in-iilation  du  Sun-.      Paris,  ISC,;;.  ,,.  :,{. 


THE    CIRCULATION.  285 

ventricle.  It  is  also  momentary  in  duration,  the  line,  after  reaching  its 
maximum  elevation,  immediately  descending  nearly  to  its  former  level. 
Then  follows  a  series  of  undulations,  due  to  the  vibration  of  the  auriculo- 
ventricular  valves,  already  closed  by  the  contraction  of  the  ventricle. 
The  pressure  in  the  relaxed  auricle  then  slowly  increases  by  the  influx 
of  blood  from  the  great  veins,  until  the  time  arrives  for  a  second  auric- 
ular contraction,  when  it  suddenly  rises  to  a  maximum  and  again  falls 
as  before.  The  ventricular  contraction,  which  follows  almost  immedi- 
ately that  of  the  auricle,  is  much  more  powerful,  but  requires  a  little 
longer  interval  to  arrive  at  its  maximum,  and  its  entire  duration  is  at 
least  three  times  as  long  as  that  of  the  auricle.  It  will  be  seen  that 
during  the  slow  filling  of  the  auricle  with  blood,  a  similar  partial 
increase  of  pressure  takes  place  in  the  ventricle ;  and  the  maximum 
pressure  in  the  auricle  corresponds  in  time,  with  a  momentary  undula- 
tion in  the  ventricle,  immediately  followed  by  the  extreme  rise  of 
pressure,  due  to  the  ventricular  contraction. 

The  exploration  of  the  left  cavities  of  the  heart  by  these  means,  is 
much  more  difficult  than  that  of  the  right,  but  Marey  succeeded,  in 
several  experiments,  in  introducing  pressure-tubes  simultaneously  into 
the  right  auricle  and  ventricle,  through  the  jugular  vein,  and  into  the 
left  ventricle  through  the  carotid  artery,  and  in  ascertaining  the  com- 
parative pressure  in  these  cavities,  as  measured  in  millimetres  of  the 
mercurial  column.  In  one  instance  the  force  indicated  by  the  different 
pressure-gauges  was  as  follows : 

PRESSURE  OF  BLOOD  IN  THE 

Right  Auricle 2.5  mm. 

Right  Ventricle 25.0    " 

Left  Ventricle 128.0    " 

The  relation  in  force  between  the  two  ventricles  varied  somewhat  in 
different  animals,  according  to  their  bodily  condition  and  the  state  of 
the  circulation ;  but  taking  all  the  observations  together,  the  force  of 
pressure  in  the  left  ventricle  was  in  general  from  three  to  five  times 
greater  than  in  the  right. 

The  pressure  to  which  the  blood  is  subjected  in  the  ventricles  is 
therefore  much  greater  than  in  the  auricles ;  and  it  is  prevented  from 
reacting  in  a  backward  direction  by  the  closure  of  the  auriculo-ventricu- 
lar  valves.  The  force  of  the  right  ventricle  is  expended  on  the  blood 
in  its  passage  through  the  pulmonary  artery  and  the  pulmonary  capil- 
laries ;  while  that  of  the  left  ventricle  is  sufficient  for  its  propulsion 
through  the  general  arterial  system. 

The  Arterial  Circulation. 

The  arteries  are  a  system  of  branching  tubes,  which  commence  with 
the  aorta  and  ramify  throughout  the  body,  distributing  the  blood  to 
the  peripheral  vascular  organs.  They  consist  of  three  principal  coats, 
namely,  an  inner  coat,  composed  of  thin  elastic  laminae  lined  with 
flattened  epithelium  cells ;  a  middle  coat,  containing  elastic  tissue  and 


286  FUNCTIONS    OF     NUTRITION. 

unstriped  muscular  fibres,  arranged  transversely  around  the  vessel ;  and 
an  external  coat  of  condensed  connective  tissue.  The  principal  differ- 
ence between  the  larger  and  smaller  arteries  is  in  the  structure  of 
their  middle  coat.  In  the  smaller  arteries  this  is  composed  exclusively 
of  muscular  fibres.  In  arteries  of  medium  size  it  contains  both  mus- 
cular and  elastic  tissue ;  while  in  those  of  the  largest  calibre  it  consists 
of  elastic  tissue  alone.  The  large  arteries,  accordingly,  have  much 
elasticity  and  but  little  contractility ;  while  the  smaller  are  contractile, 
and  less  elastic. 

Movement  of  Blood  through  the  Arterial  System. — The  movement 
of  the  blood  in  the  arteries  is  due  to  the  impulse  of  the  ventricular 
systole.  The  arterial  system  may  be  regarded  as  a  great  vascular 
cavity,  subdivided  by  the  successive  branching  of  its  vessels,  but 
communicating  freely  with  the  heart  at  one  extremity,  and  with  the 
capillary  plexus  at  the  other.  At  the  time  of  the  heart's  contraction, 
the  muscular  walls  of  the  ventricle  close  upon  its  contents ;  and  as 
the  auriculo-ventricular  valves  shut  back  and  prevent  regurgitation, 
the  blood  is  forced  out  from  the  ventricle  through  its  arterial  orifice. 
As  the  ventricle  relaxes  it  is  again  filled  with  blood  from  the  auricle, 
and  delivers  it,  as  before,  by  a  new  contraction,  into  the  arteries. 
Under  these  recurring  impulses  the  blood  moves  from  the  heart 
through  the  arterial  system. 

Arterial  Pulse. — At  each  ventricular  systole  a  charge  of  blood  is 
driven  into  the  arteries,  distending  them  by  the  additional  fluid  forced 
into  their  cavities.  When  the  ventricle  relaxes,  its  distending  force  is 
suspended;  and  the  elastic  arterial  walls,  reacting  upon  their  contents, 
would  drive  the  blood  back  into  the  heart  were  it  not  for  the  closure  ef 
the  semi-lunar  valves,  which  prevent  a  backward  movement.  The  blood 
is  accordingly  propelled,  under  the  elastic  pressure  of  the  arterial  walls, 
into  the  capillary  system.  When  the  arteries,  thus  partially  emptied, 
have  returned  to  their  previous  dimensions,  they  are  again  distended 
by  another  contraction  of  the  heart.  This  produces,  throughout  the 
arterial  system,  a  succession  of  expansions  and  reactions,  known  as  the 
arterial  pulse. 

Since  each  arterial  expansion  is  produced  by  a  ventricular  systole, 
the  pulse,  as  felt  in  any  superficial  artery,  is  a  convenient  guide  for 
ascertaining  the  character  of  the  heart's  action.  The  radial  artery  at 
the  wrist,  owing  to  its  accessible  situation,  is  usually  employed  for 
this  purpose.  Any  variation  in  the  frequency,  force,  or  regularity  of 
the  heart's  movement  is  indicated  by  a  corresponding  modification  of 
the  pulse  at  the  wrist. 

The  average  frequency  of  the  pulse  in  man  is,  for  the  adult  male  in 
a  state  of  quiescence,  70  beats  per  minute.  This  rate  may  be  accel- 
erated by  muscular  exertion.  Even  the  variation  of  muscular  effort 
between  the  standing,  sitting,  and  recumbent  postures,  will  make  a 
difference  in  the  frequency  of  the  pulse  of  from  8  to  10  beats  per 
minute.  A .«••<•  has  a  marked  influence  in  the  same  direction.  According 


THE    CIRCULATION. 


287 


to  Carpenter,  the  pulse  of  the  foetus,  before  birth,  is  about  140,  and 
that  of  the  newly-born  infant  130.  During  the  first,  second,'  and 
third  years  it  gradually  falls  to  100;  by  the  fourteenth  year  to  80; 
and  is  reduced  to  the  adult  standard  by  the  twenty-first  year.  At 
every  age,  mental  excitement  may  produce  a  temporary  acceleration, 
varying  in  degree  with  the  peculiarities  of  the  individual. 

As  a  rule,  the  rapidity  of  the  heart's  action  is  in  inverse  ratio  to  its 
force.  A  slow  pulse,  within  physiological  limits,  is  usually  a  strong 
one,  and  a  rapid  pulse  comparatively  feeble.  This  is  especially  notice- 
able in  the  lower  animals,  when  the  force  of  the  heart's  action  is 
experimentally  measured  by  the  arterial  impulse;  an  increased  fre- 
quency of  the  cardiac  pulsations  being  almost  invariably  accompanied 
by  a  diminution  in  their  strength.  The  same  is  true  in  disturbance 
of  the  heart's  action  from  morbid  causes ;  the  pulse  in  febrile  or  other 
debilitating  affections  becoming  weaker  as  it  grows  more  rapid.  An 
excessive  rapidity  of  the  pulse  is  an  indication  of  great  danger,  and, 
in  the  adult  male,  a  continued  rate  of  160  per  minute  is  almost  inva- 
riably a  fatal  symptom. 

Increased  Curvature  of  the  Arteries  in  Pulsation. — la  the  disten- 
sion of  the  arteries  under  the  force  of  the  ventricular  systole,  these 
vessels  arc  elongated  as  well  as  widened;  and  especially  in  those 
having  a  distinctly  curvilinear  or  serpentine  course,  an  elongation  and 
consequent  increase  of  curvature  is  observable  at  each  pulsation.  This 
may  be  seen  in  emaciated  persons,  in  the  temporal 
artery,  or  in  the  radial  at  the  wrist,  and  is  very 
marked  in  the  mesenteric  arteries  in  the  abdomen  of 
a  quadruped.  A  superficial  artery,  running  over  a 
bony  surface,  may  be  partially  lifted  out  of  its  bed 
from  this  cause,  at  each  pulsation.  In  old  persons 
the  arterial  curvatures  become  permanently  enlarged 
from  frequent  distension ;  and  all  the  smaller  arteries 
tend  to  assume,  with  the  advance  of  age,  a  more  ser- 
pentine course. 

Characters  of  the  Arterial  Pulse. — The  shock  of 
an  arterial  pulsation,  as  perceived  by  the  finger, 
varies  a  little  in  time,  according  to  its  distance  from 
the  centre  of  the  circulation.  If  one  finger  be  placed 
upon  the  chest  over  the  heart's  apex,  and  another 
over  the  carotid  artery  at  the  middle  of  the  neck, 
little  or  no  difference  in  time  is  perceptible  be- 
tween the  two  impulses  ;  the  distension  of  the  caro- 
tid being  sensibly  simultaneous  with  the  heart's  contraction.  But  if 
the  second  finger  be  placed  on  the  temporal  artery,  its  impulse  is  felt 
to  be  a  little  later  than  that  of  the  hsart.  The  pulse  of  the  radial 
artery  at  the  wrist  is  also  later  than  that  of  the  carotid,  and  that  of  the 
posterior  tibial  at  the  ankle  later  than  that  of  the  radial.  The  greater 
the  distance  from  the  heart,  the  later  is  the  pulsation  of  the  artery. 


Elongation  and  in- 
creased curvature 
of  an  ARTERY  IN 
PULSATION. 


288  FT  NOTIONS    OF    NUTRITION. 

But  this  difference  in  time  of  the  arterial  pulsations,  in  different 
parts  of  the  body,  is  rather  relative  than  absolute.  The  cardiac  im- 
pulse is  communicated  at  the  same  instant  to  every  part  of  the  arterial 
system,  and  the  distension  begins  in  all  the  arteries  simultaneously ; 
but  it  reaches  its  completion  more  rapidly  in  the  neighborhood  of  tin- 
heart,  more  slowly  at  a  distance.  The  arterial  pulse,  as  perceived  by 
the  finger,  marks  the  condition  of  maximum  distension;  and  this  con- 
dition occurs  at  a  later  period,  according  to  the  distance  of  the  artery 
from  the  heart. 

The  contraction  of  the  left  ventricle  is  a  brisk  and  sudden  motion. 
The  blood  driven  into  the  arterial  system,  meeting  with  a  certain 
resistance  from  that  already  in  the  vessels,  does  not  instantly  displace 
a  quantity  equal  to  its  own,  but  a  part  of  its  force  is  expended  in 
stretching  the  vascular  walls.  The  expansion  of  the  nearer  arteries 
is  therefore  sudden  and  momentary,  like  the  contraction  of  the  heart. 
But  it  still  requires  a  certain  expenditure  of  time  ;  so  that,  a  little  dis- 
tance farther  on,  the  vessel  is  not  distended  with  the  same  rapidity, 
and  the  arterial  dilatation  arrives  more  slowly  at  its  maximum. 

On  the  other  hand,  at  the  moment  of  cardiac  relaxation,  the  elastic 
reaction  of  the  larger  arteries  propels  a  portion  of  blood  into  the 
smaller  vessels  beyond,  and  thus  partially  maintains  their  distension. 
In  the  larger  arteries,  accordingly,  there  is  a  noticeable  difference  in 
size  between  the  periods  of  their  expansion  and  collapse ;  since  they 
are  fully  distended  by  the  ventricular  systole,  and  afterward  emptied, 
in  great  measure,  by  their  own  reaction.  But  in  the  smaller  arterial 
branches,  this  difference  is  not  so  marked.  They  are  less  fully  dis- 
tended at  the  time  of  the  cardiac  impulse,  because  this  force  is  partly 
expended  on  the  large  vessels ;  and  their  subsequent  reaction  is  less 
complete,  because  they  are  then  subjected  to  the  elastic  pressure  from 
the  arterial  trunks.  This  produces  a  gradual  modification  of  the  arte- 
rial pulse,  from  the  heart  toward  the  periphery. 

The  mechanism  of  this  change  is  illustrated  in  the  experiments  of 
Marey,*  by  means  of  an  elastic  tube  attached  to  a  forcing  pump,  and 
open  at  its  farther  extremity.  At  different  points  on  the  tube  are  small 
levers,  which  are  lifted  by  its  distension  when  water  is  driven  into  it 
from  the  forcing  pump.  Each  lever  carries  at  its  extremity  a  small 
pencil,  which  marks  upon  a  strip  of  paper,  moving  with  uniform  rapid- 
ity, the  curves  of  its  elevation  and  depression.  By  these  curves  both 
the  extent  and  rapidity  of  the  distension  of  different  parts  of  the  tube 
may  be  registered,  as  shown  in  Fig.  GT.  - 

From  this  it  appears  that  the  distension  produced  by  the  stroke  of 
the  forcing  pump  begins  at  the  same  moment  throughout  the  tube,  and 
that  the  pulsation  is  everywhere  of  equal  length.  But  near  the  com- 
mencement of  the  tube,  its  expansion  is  wide  and  sudden,  lasting-  for 
only  one-sixth  part  of  the  entire  pulsation,  while  the  remaining  live- 

*  Journal  cle  la  Physiologic.     Paris,  Avril,  1859. 


THE    CIRCULATION. 


289 


sixths   are   occupied   by  its   reaction.      At   more   remote   points   the 
time  of  expansion  becomes  longer  and  that  of  collapse  shorter ;  until 

FIG.  67. 


CURVES  OF  PULSATION  IN  AN  ELASTIC  TUBE.— 1.  Near  the  distending  force.   2.  At  a  distance 
from  it.    3.  Still  farther  removed. 

finally,  at  a  certain  distance,  the  amount  of  expansion  is  reduced  one- 
half,  and  the  two  periods  are  equalized  in  duration. 

Registration  of  Pulse  by  the  Sphygmograph. — The  frequency  and 
character  of  the  arterial  pulse  may  be  permanently  recorded  by  the 
use  of  an  instrument  similar  in  principle  to  the  cardiograph,  but  adapted 
for  application  to  an  artery.  This  instrument,  of  which  there  are  vari- 
ous modifications,  is  the  Sphygmograph.  It  consists  essentially  of  a 
small  ivory  or  metallic  plate,  gently  pressed  upon  the  artery  by 
means  of  a  fine  spring,  so  as  to  rise  and  fall  with  the  expansion 
and  collapse  of  the  arterial  tube.  The  plate  communicates  its  motion, 
through  a  vertical  metallic  rod,  to  a  registering  lever  above.  The 
oscillating  extremity  of  the  lever,  when  the  instrument  is  in  opera- 
tion, thus  indicates  the  movements  of  the  artery,  and  marks  upon 
a  strip  of  paper  the  frequency  and  form  of  its  pulsations. 

The  advantage  of  such  an  instrument  is,  first,  that  the  length  of  the 
lever  magnifies  to  the  eye  the  extent  of  the  arterial  oscillations,  and] 
thus  enables  us  to  perceive  movements  too  delicate  to  be  distinguished 
by  the  touch ;  and,  secondly,  that,  each  part  of  a  pulsation  being  per- 
manently registered,  the  most  momentary  changes  may  be  afterward 
studied  at  leisure  and  compared  with  each  other. 

By  this  means  it  has  been  shown,  that,  while  there  is  a  general 
resemblance  in  the  form  of  pulsation  of  different  arteries,  nearly  every 
vessel  to  which  the  instrument  can  be  applied  presents  peculiarities 

FIG.  68.  ' 


TRACE  OF  THE  RADIAL  PULSE,  taken  by  the  Sphygmograph. 

dependent  on  its  size,  position,  and  distance  from  th.e  heart.  In  the 
radial  artery  at  the  wrist,  each  pulsation  consists  of  a  sudden  expan- 
sion of  the  vessel,  indicated  by  a  rapid  upward  movement  of  the  lever, 
making,  in  the  trace,  a  straight,  nearly  vertical  line.  This  is  fol- 

T 


290 


FUNCTIONS    OF    NUTRITION. 


lowed  by  a  gradual  descent  corresponding  with  the  collapse  of  the 
artery,  until  it  reaches  the  lowest  point  of  the  trace,  when  the  ascend- 
ing movement  again  takes  place,  and  so  on  alternately.  The  line  of 
descent  is  marked  by  one,  two,  or  three  slight  undulations,  indicating 
a  corresponding  variation  in  the  tension  of  the  artery  during  its  col- 
lapse. 

These  undulations  in  the  line  of  descent,  in  the  sphygmograph 
tracing,  are  due  to  an  oscillation  in  the  mass  of  the  blood,  subse- 
quent to  the  impulse  of  the  heart,  and  during  the  reaction  of  the  arte- 
rial system.  Marey*  has  shown  that  similar  oscillations  are  produced 
when  any  incompressible  liquid  is  driven  by  a  sudden  impulse  into 
an  elastic  tube  ;  and  that  they  may  be  indicated  by  a  similar  movement 
of  the  index  of  a  sphygmograph.  When  the  heart's  impulse  is  moder- 
ate, and  the  tension  of  the  arterial  system  fully  developed,  the  undula- 
tions in  the  descending  line  of  the  pulse  are  not  very  perceptible ; 
but  when  the  heart's  impulse  is  more  rapid,  and  the  arterial  tension 
diminished,  the  undulations  become  more  marked.  Traces  of  different 
form,  in  this  respect,  may  be  produced  in  the  same  individual  by  arti- 
ficial variations  in  the  temperature  of  the  body.  The  following  are 
three  traces  of  the  radial  pulse  obtained  in  his  own  person  by  Marey, 
by  increasing  the  quantity  of  clothing  at  intervals  of  twenty  minutes : 

Fia.  69. 


FIG.  70. 


FIG.  71. 


VARIATIONS  OF  TIIK  RADIAL  PULSE,  uutk-r  the  intlm-nci-  of  im  iva.snl 


(Murey.) 


Dicrotic  Pulse.  —  In  certain  conditions,  accompanied  by  rapid  j  HI  lo- 
tion of  the  heart  with  diminished  arterial  tension,  the  secondary  oscil- 
lation of  the  artery  becomes  so  marked,  in  proportion  to  the  original 
impulse,  that  it  is  perceived  by  the  finger,  and  thus  the  pulse  is  ap. 
parently  doubled  ;  that  is,  there  are  two  pulsations  of  the  artery 
for  each  contraction  of  the  heart,  namely,  one  due  to  the  original 

*  Physiologic  M^dicale  de  la  Circulation  du  Sang.    Paris,  1863,  p.  266. 


THE    CIRCULATION. 


291 


impulse,  and  another  caused  by  the  oscillation  of  blood  in  the  feebly 
distended  artery.  This  is  the  dicrotic  pulse,  often  present  in  diseases 
of  a  typhoid  character. 


FIG.  72. 


DICKOTIC  PULSE  OF  TYPHOID  PNEUMONIA.    (Marey.) 
FIG.  73. 


DICROTIC  PULSE  OF  TYPHOID  FEVER.    (Marey.) 


It  is  evident  that  the  dicrotic  character  of  the  pulse  is  not  altogether 
peculiar  to  diseased  conditions,  since  it  exists  in  some  degree,  as  shown 
by  the  preceding  figures,  even  in  health.  But  it  is  usually  too  slight 
to  be  perceptible  by  the  finger  unless  exaggerated  from  morbid  causes. 

The  mechanism  of  the  dicrotic  pulse  has  been  demonstrated  by 
Koschlakoff.*  If  a  liquid  be  driven  by  a  sudden  impulse  through 
an  elastic  tube,  connected  with  two  separate  pressure  gauges,  one 
near  the  point  of  entrance  of  the  liquid,  the  other  near  its  exit, 
the  liquid  will  rise  in  the  first  gauge  before  the  increased  pressure 
reaches  the  second;  it  then  falls  while  the  second  is  rising,  and  again 
rises  while  the  second  falls ;  showing  an  alternate  increase  and 
diminution  of  pressure  in  the  two  extremities  of  the  tube.  This 
alternation  continues  until  the  pressure  is  equalized,  or  until  the  tube 
is  again  distended  by  a  new  impulse. 

Pulsating  Flow  of  Blood  in  the  Arteries. — Owing  to  the  alternate 
contraction  and  relaxation  of  the  heart,  the  blood  moves  through  the 
arterial  system  in  a  series  of  impulses ;  and  in  hemorrhage  from  a 
wounded  artery  the  blood  flows  in  successive  jets,  as  well  as  more 
rapidly  than  if  it  came  from  veins  or  capillaries.  If  a  slender  canula 
be  introduced  through  the  walls  of  the  left  ventricle,  in  the  exposed 
heart  of  a  living  animal,  the  flow  of  blood  from  its  orifice  is  inter- 
mittent. A  strong  jet  takes  place  at  each  ventricular  contraction,  and 
is  interrupted  at  the  time  of  relaxation.  But  if  the  puncture  be  made 
in  a  large  artery  near  the  heart,  the  blood  is  discharged  from  it  in  a 
continuous  stream  ;  only  its  flow  is  abundant  at  the  time  of  ventricular 
contraction,  and  more  scanty  at  the  time  of  relaxation.  The  disten- 
sion and  elasticity  of  the  arterial  walls  modify  the  effects  of  the  separate 
arterial  pulsations,  and  partially  fuse  them  with  each  other ;  produc- 
ing, in  the  larger  and  medium-sized  arteries,  a  movement  of  the  blood 

*  In  Lorain,  Etudes  de  Medecine  Clinique.     Paris,  1870,  p.  75. 


292  FUNCTIONS    OF    NUTRITION. 

which  increases  at  each  cardiac  impulse,  and  diminishes  during  relaxa- 
tion. 

Equalization  of  the  Blood-current  in  the  Arterial  System. — Since 
the  distensible  and  elastic  properties  of  the  arterial  walls  make  the  flow 
of  blood  more  continuous  than  it  would  otherwise  be,  this  effect 
increases  as  the  blood  moves  through  the  arterial  system.  A  part 
of  the  force  of  each  pulsation  is  absorbed,  for  the  time  being,  in 
the  distension  of  the  artery,  and  is  again  returned  in  an  impulse  to 
the  blood  at  the  following  interval,  by  the  reaction  of  the  vessel.  The 
farther  from  the  heart  the  blood  recedes,  the  greater  becomes  the 
influence  of  the  intervening  arteries ;  and  thus  the  remittent  or  pulsating 
character  of  the  arterial  current,  which  is  strongly  pronounced  in  the 
vicinity  of  the  heart,  becomes  gradually  diminished  during  its  passage 
through  the  vessels,  until  in  the  smaller  arteries  it  is  hardly  per- 
ceptible. 

The  influence  of  an  elastic  medium,  in  equalizing  the  flow  of  an  in- 
terrupted current,  may  be  shown  by  injecting  water  from  a  force-pump 
alternately  through  two  tubes,  one  of  India-rubber,  the  other  of  metal. 
Whatever  be  the  length  of  the  metallic  tube,  the  water  will  be 
delivered  from  its  extremity  in  distinct  jets,  corresponding  with  the 
strokes  of  the  piston :  but  when  it  is  replaced  by  an  elastic  tube  of 
sufficient  length,  the  separate  impulses  are  merged  into  each  other, 
and  the  water  is  discharged  in  a  continuous  stream. 

The  elasticity  of  the  arteries  never  completely  neutralizes  the  eifect 
of  the  cardiac  contractions,  since  a  pulsation  can  be  seen  in  the  flow 
of  blood  in  even  the  smallest  arteries,  when  examined  under  the  mi- 
croscope ;  but  it  diminishes  in  degree  from  the  heart  outward,  and 
the  current  becomes  nearly  continuous  at  the  confines  of  the  capillary 
system. 

The  Arterial  Pressure. — The  arterial  circulation,  as  shown  by  the 
above  facts,  is  the  combined  result  of  two  different  forces ;  namely,  the 
contraction  of  the  heart,  by  which  the  blood  is  propelled  in  successive 
impulses,  and  the  elasticity  of  the  arteries,  by  which  it  is  subjected  to 
a  continuous  pressure. 

If  one  of  the  larger  or  medium-sized  arteries  be  divided,  in  the  living 
animal,  and  a  glass  tube  of  the  same  diameter  fixed  in  its  orifice 
in  the  vertical  position,  the  blood  will  rise  in  the  tube  to  a  height 
of  five  and  a  half  or  six  feet,  and,  until  coagulation  occurs,  will  continue 
to  oscillate  about  this  level.  The  column  of  fluid  thus  supported  in- 
dicates the  pressure  to  which  the  blood  is  subjected  within  the  vessels. 
This  force,  due  to  the  reaction  of  the  arterial  system,  is  known  as  the 
arterial  pressure. 

The  arterial  pressure  is  best  measured  by  connecting  an  open  artery, 
by  means  of  a  flexible  tube,  with  a  small  reservoir  of  mercury,  provided 
with  a  narrow  upright  graduated  tube,  open  at  its  upper  extremity. 
When  the  mercury  in  the  reservoir  is  exposed  to  the  pressure  of  tin- 
blood,  it  rises  in  the  upright  tube  to  a  corresponding  level. 


THE    CIRCULATION.  293 

The  average  arterial  pressure,  in  the  dog  and  other  animals  of  similar 
size,  is  equivalent  to  a  column  of  mercury  150  millimetres  in  height. 
But  while,  in  such  an  instrument,  connected  with  the  arterial  system, 
the  mercurial  column  indicates  on  the  whole  an  average  pressure,  it 
also  exhibits  two  series  of  oscillations ;  showing  a  fluctuation  in  the 
degree  of  pressure,  owing  to  two  different  causes. 

One  of  these  oscillations  is  synchronous  with  respiration.  At  every 
inspiration,  the  level  of  the  mercury  falls  somewhat,  with  every  expira- 
tion it  rises.  As  the  movement  of  inspiration  consists  in  an  expansion 
of  the  chest  cavity,  its  effect  is  to  diminish  the  pressure  on  the  heart 
and  great  blood-vessels,  and  consequently  to  lower  in  a  similar  degree 
the  tension  of  the  whole  arterial  system.  In  expiration,  on  the  other 
hand,  the  thoracic  walls  return  to  their  former  position,  and  the  pressure 
on  the  organs  within  the  chest  is  reestablished.  These  changes  are 
indicated  by  corresponding  variations  in  the  height  of  the  mercurial 
column.  The  oscillations  due  to  this  cause,  however,  are  not  uniform, 
but  vary  according  to  the  condition  of  the  respiratory  movements. 
When  respiration  is  active  and  labored,  they  may  reach  the  extent 
of  30  millimetres ;  when  it  is  quiet,  as  in  an  animal  deeply  etherized, 
they  may  be  nearly  imperceptible. 

The  remaining  oscillation  is  more  uniform,  and  is  due  to  the  cardiac 
pulsations.  It  consists  of  comparatively  rapid  undulations  of  the  mer- 
curial column,  simultaneous  with  the  movements  of  the  heart.  At 
every  ventricular  contraction  the  mercury  rises  12  or  15  millimetres, 
and  at  every  relaxation  falls  to  its  previous  level.  The  instrument 
thus  indicates  the  intermitting  pressure  of  the  heart's  action ;  and  has 
accordingly  received  the  name  of  the  cardiometer.  As  the  average 
height  of  the  column  in  the  cardiometer  is  150  millimetres,  and  as  it 
varies  by  15  millimetres  under  the  influence  of  the  cardiac  pulsations, 
it  appears  that  each  contraction  of  the  heart  is  superior  in  force  to  the 
resistance  of  the  arteries  by  about  one-tenth ;  and  the  arterial  system 
is,  therefore,  kept  full,  and  the  arterial  tension  maintained,  notwith- 
standing the  constant  discharge  of  blood  into  the  capillaries. 

Rapidity  of  the  Arterial  Current. — The  blood  moves  in  the  arteries 
more  rapidly  than  in  any  other  part  of  the  vascular  system.  Its  exact 
rate  varies  according  to  the  situation  of  the  vessel  and  the  period  of  the 
pulsation ;  being  greatest  in  the  immediate  neighborhood  of  the  heart, 
and  diminishing  from  this  point  outward.  The  division  of  the  arterial 
trunks  into  branches  and  ramifications  increases  their  surface  of  con- 
tact with  the  blood ;  and  the  increased  adhesion  produced  by  this  con- 
tact retards  the  current,  which  is  accordingly  slower  in  the  small 
arteries  than  in  those  of  large  or  medium  size.  In  the  smallest  arteries, 
as  seen  under  the  microscope  in  the  transparent  tissues,  the  partial 
adhesion  of  the  blood  to  the  vascular  wall,  and  the  greater  rapidity 
of  its  flow  in  the  axis  of  the  vessel  are  readily  perceptible.  The  con- 
sistency of  the  circulating  fluid,  however,  and  the  smoothness  of  the 
internal  surface  of  the  arteries,  are  such  that  this  obstacle  to  the  move- 


294  FUNCTIONS    OF    NUTRITION. 

ment  of  the  blood  has  only  a  partial  retarding  influence ;  and  even  in 
the  smallest  arteries  its  flow  is  so  rapid  that  the  separate  blood-globules 
cannot  be  distinguished,  but  only  a  mingled  current  shooting  forward 
with  increased  velocity  at  each  pulsation. 

The  average  rapidity  of  the  blood  stream  in  the  larger  arteries,  in 
dogs,  horses,  and  calves,  was  determined  by  Volkrnann,  as  30  centi- 
metres per  second.  The  most  exact  experiments  on  this  point  are  those 
of  Chauveau,*  who  introduced  into  the  carotid  artery  of  the  horse  a 
thin  brass  tube,  about  five  centimetres  long  and  eight  or  nine  millime- 
tres in  diameter.  The  tube  was  introduced  through  a  longitudinal 
incision  in  the  walls  of  the  vessel,  and  secured  by  a  ligature  near  each 
extremity ;  so  that  the  arterial  current  might  pass,  without  serious  ob- 
struction, through  the  tube  forming,  for  the  time,  a  part  of  the  arterial 
walls.  In  the  side  of  the  tube  was  a  small  opening,  three  millimetres 
long  by  one  and  a  half  millimetre  wide,  closed  by  an  elastic  membrane, 
so  secured  as  to  prevent  the  escape  of  blood.  Through  the  centre  of 
the  membrane  was  passed  a  light  metallic  needle,  the  inner  extremity 
of  which,  somewhat  flattened  in  shape,  received  the  impulse  of  the 
blood ;  while  the  outer  portion,  prolonged  into  a  slender  index,  marked 
upon  a  semicircular  scale  the  oscillations  of  the  inner  extremity,  and 
consequently  the  varying  rapidity  of  the  arterial  current.  The  actual 
velocity,  indicated  by  any  given  oscillation  of  the  needle,  was  ascer- 
tained beforehand  by  attaching  the  apparatus  to  an  elastic  tube  and 
passing  through  it  a  stream  of  warm  water  of  known  rapidity. 

The  details  of  the  circulatory  movement,  as  indicated  by  these  exper- 
iments, differ  somewhat  in  the  larger  and  the  smaller  arteries. 

a.  In  the  carotid  artery,  at  the  instant  of  ventricular  systole,  the 
blood  is  suddenly  put  in  motion  with  a  high  velocity,  amounting  on 
the  average  to  a  little  over  50  centimetres  per  second. 

At  the  termination  of  the  systole,  and  immediately  before  the  closure 
of  the  aortic  valves,  the  movement  of  the  blood  decreases  considerably, 
and  may  even,  for  the  time,  be  completely  arrested. 

At  the  instant  of  closure  of  the  valves,  the  circulation  receives  a 
new  impulse,  and  the  blood  again  moves  forward  with  a  velocity  of 
rather  more  than  20  centimetres  per  second. 

Afterward,  the  rapidity  of  the  current  gradually  diminishes  during 
the  heart's  inaction,  until,  at  the  end  of  this  period  and  just  before 
a  new  systole,  it  is  reduced,  on  the  average,  to  15  centimetres  per 
second. 

b.  In  the  smaller  arteries,  such  as  the  facial,  the  movement  of  the 
blood  is  more  uniform.     At  the  moment  of  the  heart's  systole  it  is  less 
rapid  than   in  the  carotid;  and  on  the  other  hand,  it  has  a  greater 
velocity  during  the  period  of  ventricular  repose.     The  secondary  im- 
pulse,  following   the  closure  of  the  aortic  valves,   is  less  pen-eptiMe 
than  in  the  larger  nrt< -rirs,  and  may  even  be  altogether  absent. 


tic  l:i  Physioli.-ii'.      l':iris,  Ootobiv,  18(i(),  p.  01)5. 


THE    CIRCULATION.  295 

The  Venous  Circulation. 

The  veins,  like  the  arteries,  are  composed  of  three  coats an  inner, 

middle,  and  exterior ;  but  they  contain  a  smaller  quantity  of  muscular 
and  elastic  fibres,  and  a  larger  proportion  of  condensed  connective 
tissue.  They  are  consequently  more  flaccid  and  compressible  than 
the  arteries,  and  less  elastic  and  contractile.  They  are  furthermore 
distinguished,  in  the  limbs,  neck,  and  external  parts  of  the  head  and 
trunk,  by  being  provided  with  valves,  in  the  form  of  festoons,  so  placed 
that  they  allow  the  blood  to  pass  from  the  periphery  toward  the  heart, 
but  prevent  its  reflux  in  the  opposite  direction. 

Though  the  walls  of  the  veins  are  thinner  and  less  elastic  than  those 
of  the  arteries,  yet  their  capacity  for  resistance  to  pressure  is  equal,  or 
even  superior.  Milne  Edwards*  has  collected  the  results  of  various 
experiments,  which  show  that  the  veins  will  sometimes  bear  a  pressure 
sufficient  to  rupture  the  arteries.  In  one  instance  the  jugular  vein 
supported  a  pressure  equal  to  a  column  of  water  148  feet  in  height ; 
and  in  another,  the  iliac  vein  of  a  sheep  resisted  a  pressure  of  more 
than  four  atmospheres.  The  portal  vein  resisted  a  pressure  of  six 
atmospheres ;  and  in  one  case,  in  which  the  aorta  of  a  sheep  was  rup- 
tured by  a  pressure  of  72  kilogrammes,  the  vena  cava  of  the  same 
animal  supported  a  pressure  of  80  kilogrammes. 

This  property  of  the  veins  is  due  to  the  white  fibrous  tissue  in  their 
composition ;  the  same  tissue  which  forms  nearly  the  whole  of  the 
tendons  and  fasciaB,  and  which  is  distinguished  by  its  density  and 
unyielding  nature. 

The  elasticity  of  the  veins,  on  the  other  hand,  is  much  less  than  that 
of  the  arteries,  and  there  is  consequently  but  little  variation  in  their 
calibre.  When  filled  with  blood,  they  swell  to  a  certain  size ;  when 
empty,  their  sides  collapse,  and  remain  in  contact  with  each  other. 

Another  peculiarity  of  the  venous  system  consists  in  its  numerous 
communicating  channels. 

In  injected  preparations,  two,  three,  or  more  veins  are  often  seen 
coming  from  the  same  region,  with  frequent  transverse  communica- 
tions. The  deep  veins  accompanying  the  main  arteries  of  the  limbs 
inosculate  freely  with  each  other,  and  also  with  the  superficial  veins. 
Among  those  coming  from  the  head,  the  external  jugulars  communi- 
cate with  the  thyroid,  the  anterior  jugular,  and  the  brachial  veins.  The 
external  and  internal  jugulars  communicate  with  each  other,  and  the 
two  thyroid  veins  form  an  abundant  plexus  in  front  of  the  trachea. 

Thus  the  blood,  coming  from  the  periphery  toward  the  heart,  flows 
in  a  number  of  communicating  channels;  through  which  it  passes, 
under  different  conditions  of  pressure,  by  a  variety  of  routes,  but 
always  in  the  same  direction. 

Movement  of  the  Blood  through  the  Venous  System.. — The  flow  of 


s  stir  la  Physiologie.     Paris,  1859,  tome  iv.,  p.  301. 


296 


FUNCTIONS    OF    NUTRITION. 


blood  through  the  veins  is  less  powerful  and  regular  than  that  through 
the  arteries.     It  depends  on  the  action  of  three  different  forces. 

I.  The  most  important  of  these  forces  is  the  pressure  from  the  capil- 
lary circulation.  The  blood  moves  from  the  arteries  into  and  through 
the  capillary  vessels,  under  an  impulse  derived  originally  from  the  heart, 
and  afterward  replaced  by  the  comparatively  uniform  arterial  pressure. 
This  pressure  is  not  entirely  exhausted  in  the  capillaries ;  and  the  blood 
accordingly  emerges  from  these  vessels  and  enters  the  venous  system 
with  a  force  sufficient  to  fill  its  rootlets,  and  to  pass  thence  into  its  larger 
branches  and  trunks.  As  the  veins  converge  from  the  periphery  toward 
the  centre,  and  unite  into  trunks  of  larger  calibre,  their  extent  of  contact 
with  the  circulating  fluid,  and  their  resistance  to  its  movement,  constantly 
diminishes;  while  the  contractions  of  the  right  ventricle  relieve  the 


FIG.  74. 


Fie!.  75. 


VEIN  with  valves  open. 


VEIN  with  valves  closed  ;  stream  of  blood  pass- 
ing off  by  a  lateral  channel. 


returning  current  from  the  obstacle  of  its  accumulation.  The  contin- 
uous pressure  of  the  blood  from  the  capillaries  thus  supplies  an 
effective  cause  for  its  movement  through  the  veins. 

II.  The  flow  of  blood  through  the  veins  is  aided  in  great  measure  by 
the  contraction  of  the  voluntary  muscles.  The  veins  in  the  limbs,  and 
in  the  parietes  of  the  head  and  trunk,  lie  among  voluntary  muscles  which 
are  often  in  a  state  of  alternate  contraction  and  relaxation.  At  each 
contraction  the  muscles  become  swollen  laterally,  thus  compressing  the 
veins  between  them.  As  the  blood,  expelled  by  this  pressure,  cannot 
regurgitate  toward  the  capillaries,  owing  to  the  closure  of  the  venous 
valves,  it  is  forced  onward  toward  the  heart ;  and  when  the  muscle 
relaxes  and  the  vein  is  liberated  from  pressure,  it  is  again  filled  from 
behind,  and  the  circulation  goes  on  as  before. 

The  muscular  system  acts  in  this  way  by  communicating  to  the  venous 
current  indirect  impulses  of  frequent  repetition,  which,  combined  with 


THE    CIRCULATION.  297 

the  action  of  the  valves,  urge  the  blood  from  the  periphery  toward  the 
heart. 

III.  A  third  cause,  contributing  to  the  movement  of  the  venous 
blood,  is  the  force  of  aspiration  exerted  by  the  thorax.  The  expan- 
sion of  the  chest  in  inspiration  diminishes  the  pressure  upon  its  con- 
tents, and  consequently  tends  to  draw  into  the  thorax  any  fluids  which 
can  gain  access  to  it.  The  expanded  cavity  is  principally  filled  by  the 
entrance  of  atmospheric  air  through  the  trachea  and  bronchi.  But  the 
blood  in  the  neighboring  veins  is  solicited  at  the  same  time  in  a  simi- 
lar direction.  The  influence  of  this  force  extends  indirectly  through- 
out the  venous  system,  each  expansion  of  the  chest  diminishing  the 
resistance  at  the  centre  of  the  circulation,  and  thus  causing  an  in- 
creased flow  toward  the  intra-thoracic  veins,  while  the  remainder  are 
filled  from  behind  as  they  are  emptied  in  front. 

Rapidity  of  the  Venous  Current. — With  regard  to  the  rapidity  of 
the  venous  current,  no  results  have  been  obtained  by  direct  experi- 
ment. Owing  to  the  flaccidity  of  the  veins,  and  the  readiness  with 
which  the  flow  of  blood  through  them  is  disturbed,  it  is  not  possible 
to  determine  this  point,  in  the  same  manner  as  for  the  arteries.  But 
a  calculation  has  been  made,  based  on  the  comparative  capacity  of  the 
arterial  and  venous  systems.  As  the  blood  which  passes  outward 
through  the  arteries  returns  through  the  veins,  the  rapidity  of  its 
flow  in  each  direction  must  be  in  inverse  ratio  to  the  capacity  of  the 
vessels.  The  entire  venous  system,  when  distended  by  injection,  con- 
tains about  twice  as  much  fluid  as  the  arteries.  During  life,  however, 
the  venous  system  is  at  no  time  so  completely  filled  with  blood  as  the 
arteries ;  and,  allowing  for  this  difference,  it  may  be  estimated  that 
the  entire  quantity  of  venous  blood  is  to  the  entire  quantity  of  arterial 
blood  nearly  as  three  to  two.  The  velocity  of  the  "blood  in  the  veins, 
as  compared  with  that  in  the  arteries,  is  therefore  as  two  to  three ;  and 
if  we  regard  the  average  rapidity  of  the  arterial  current,  according  to 
Volkmann's  experiments,  as  30  centimetres  per  second,  this  would  give 
the  movement  of  blood  in  the  veins  as  about  20  centimetres  per  second. 
This  estimate,  however,  is  only  approximative ;  since  the  venous  circu- 
lation varies,  according  to  many  circumstances,  in  different  parts  of  the 
body.  It  may  nevertheless  be  considered  as  expressing  with  sufficient 
accuracy  the  general  relative  velocity  of  the  arterial  and  venous  currents 
in  corresponding  parts  of  their  course. 

The  Capillary  Circulation. 

The  capillary  blood-vessels  are  minute  inosculating  tubes,  which  per- 
meate the  vascular  organs,  and  bring  the  blood  into  close  proximity 
with  their  tissues.  They  are  continuous,  on  the  one  hand,  with  the 
terminal  ramifications  of  the  arteries,  and,  on  the  other,  with  the  com- 
mencing rootlets  of  the  veins.  They  vary  somewhat  in  size  in  differ- 
ent tissues,  their  average  diameter  in  man  being  about  10  mmm.,  or 
yi^  of  a  millimetre.  According  to  Kolliker,  the  largest  capillaries  are 


298  FUNCTIONS    OF    NUTRITION. 

in  the  glands  and  the  osseous  tissue,  where  they  reach  the  diameter 
of  15  mmm. ;  while  the  smallest,  in  the  muscles,  the  nerves,  and  the 
retina,  are  4.5  mmm.,  that  is,  almost  exactly  the  size  of  the  smallest  of 
the  red  globules  of  the  blood. 

As  the  arterial  ramifications  approach  the  capillary  system,  they 
diminish  in  size,  and  lose  their  external  coat  of  connective  tissue. 
Their  middle  coat  is,  at  the  same  time,  reduced  to  a  single  layer  of 
fusiform  muscular  fibres,  which  become  gradually  less  numerous,  and 
at  last  disappear  altogether.  The  vascular  canal  is  thus  finally  com- 
posed only  of  a  single  tunic  continuous  with  the  internal  coat  of  the 
arterial  ramifications. 

The  capillary  blood-vessel,  in  its  recent  condition,  when  extracted 
from  any  soft  vascular  tissue,  appears  to  consist  of  a  simple,  nearly 
homogeneous  tubular  membrane,  with  flattened  oval  nuclei  placed  at 
short  distances  from  each  other,  and  projecting  slightly  into  its  cavity. 

But  if  the  vessel  be  treated  with  a 
weak  solution  of  silver  nitrate,  its 
inner  surface  becomes  marked  off  into 
regular  spaces,  each  of  which  includes 
a  nucleus ;  indicating  that  its  appar- 
ently homogeneous  tunic  is  com- 
posed of  flattened  epithelium-like 
cells,  united  with  each  other  at  their 
adjacent  edges  by  an  intervening 
cement.  It  is  this  intervening  sub- 
stance which  becomes  darkened  by 
silver  nitrate,  bringing  into  view  the 
outlines  of  the  epithelium  cells  of 
the  vascular  wall. 

The  form  of  the  cells  varies  in  dif- 

"^^^  with  its  musomar  tunic  (a),  k™t    regionS    ™d    in    Capillaries    of 
breaking  up  into   capillaries.     From  the  different   Calibre.      According   to  Kb'l- 

pi*  mater.  \\kcr,  |n  ^  smaner  capillary  blood- 

vessels, from  4.5  to  7  mmm.  in  diameter,  they  are  narrow,  elongated, 
and  fusiform,  as  in  Fig.  77  ;  often  curled  from  side  to  side,  so  as  to 
form  each  a  half  cylinder,  two  of  them  joining  at  their  edges  to  com- 
plete the  capillary  tube,  and  intercalated  at  their  ends  between  the 
adjacent  cells.  In  the  larger  capillaries,  from  8  to  15  mmm.  in  diam- 
eter, the  cells  are  shorter  and  wider,  like  those  of  ordinary  pave- 
ment epithelium.  Owing  to  this  structure  of  tlvr  capillary  blood-vessels, 
the  vascular  system,  in  the  opinion  of  some  hi<tologists,  is  to  be 
regarded  as  a  series  of  intercellular  canals,  provided,  in  different 
regions,  with  additional  layers  of  muscular,  elastic,  or  connective 
tissue. 

The  capillary  blood-vessds  are  distinguished  i>y  their  frequent  inos- 
culation, The  arteries  divide  and  subdivide,  MS  they  pass  from  within 
oiituanl,  while  the  veins  as  eonstantly  unite  with  each  other,  to  form 


THE    CIRCULATION. 


299 


larger  branches  and  trunks,  from  the  periphery  toward  the  centre ; 
and  although  the  arteries  always  present  inosculation  in  certain 
regions,  and  the  veins  more  frequently  still,  this  is,  nevertheless,  a 
secondary  feature  in  both  vascular  systems.  The  arteries  are  essen- 
tially diverging  tubes  to  distribute  the  blood  from  within  outward ;  the 
veins  are  converging  channels  to  transport  it  from  without  inward. 

The  capillaries,  on  the  other  hand,  are  mainly  characterized  by  their 
constant  and  repeated  intercommunication  ;  uniting  with  each  other  at 
such  short  intervals,  as  to  form  an  interlacing  network,  known  as  the 
capillary  plexus.  The  vessels  of  the  plexus  vary  somewhat  in  size, 
number,  and  arrangement  in  different  parts ;  but  in  every  vascular 
tissue  there  are  certain  spaces  or  islets,  surrounded  by  the  capillaries, 
and  into  which  they  do  not  penetrate.  Such  intervascular  spaces  must 
therefore  obtain  their  nourishment  by  exudation  and  absorption  through 
the  capillary  walls  and  the  intervening  tissue. 

FIG.  77. 


CAPILLARY  BLOOD-VESSEL,  from  the  tail  of  the  tadpole ;  showing  the  outlines  of  its  epithelium- 
like  cells,  rendered  visible  by  the  action  of  silver  nitrate.    (Kolliker.) 

The  special  arrangement  of  the  capillary  blood-vessels,  and  the  form 
and  size  of  the  meshes  of  their  network,  are,  in  general,  characteristic 
of  each  organ  and  tissue.  In  the  muscles,  the  intervascular  spaces  are 
long  parallelograms,  corresponding  with  the  muscular  fibres;  in  the 
mucous  membrane  of  the  stomach,  they  are  hexagonal  or  irregularly 
circular,  inclosing  the  orifices  of  the  gastric  follicles ;  in  the  papillae, 
of  the  tongue  and  skin,  and  in  the  placental  tufts,  the  capillaries  form 
twisted  vascular  loops;  in  the  glomeruli  of  the  kidneys,  convoluted 
coils;  in  the  connective  tissue,  irregularly  shaped  figures,  like  those 
included  by  the  fibrous  bundles  which  they  supply. 


300 


FUNCTIONS    OF    NUTRITION. 


The  capillary  blood-vessels  are  most  abundant,  and  connected  by  the 
closest  inosculations  in  organs  where  the  blood  serves  for  other  pur- 
poses than  local  nutrition  ;  such  as  aeration,  secretion,  or  absorption. 
One  of  the  finest  capillary  networks  is  that  of  the  lungs,  in  which  the 
diameter  of  the  intervascular  spaces  is  sometimes  a  little  greater  and 
sometimes  a  little  less  than  that  of  the  capillaries  themselves.  In  the 
intra-lobular  plexus  of  the  liver,  they  are  only  a  little  wider  than  the 
vessels  forming  the  network.  In  the  nerves,  the  serous  membranes 
and  the  tendons,  on  the  other  hand,  the  capillaries  are  less  closely 
interwoven ;  and  in  the  adipose  tissue  they  form  wide  meshes,  em- 
bracing the  fat  vesicles. 

Movement  of  the  Blood  in  the  Capillary  Vessels, — The  motion  of 
the  blood  through  the  capillaries  may  be  studied,  under  the  microscope, 
in  any  transparent  tissue  of  sufficient  vascularity.  The  frog  is  the 
most  convenient  animal  for  this  purpose,  owing  to  the  readiness  with 
which  the  circulation  will  go  on  in  the  exposed  organs  at  ordinary  tem- 
peratures. To  secure  immobility,  the  brain  and  medulla  oblongata 
should  be  broken  up  by  a  needle  introduced  through  the  cranium,  or 
the  voluntary  muscles  paralyzed  by  the  subcutaneous  injection  of  six 
drops  of  a  filtered  watery  solution  of  woorara,  made  in  the  proportion 
of  one  part  to  five  hundred.  The  body  should  be  enveloped  in  a  loose, 
moistened  bandage,  to  prevent  desiccation.  The  tongue,  the  web  of 
the  foot,  the  pulmonary  membrane,  the  mesentery  or  the  bladder  may 
be  used  to  exhibit  the  capillary  circulation,  which,  with  the  aid  of 
appropriate  mechanical  appliances,  may  be  maintained  in  either  of  these 
regions  for  several  hours. 

When  examined  in  this  man- 
ner, the  smaller  arterial  ramifi- 
cations, the  capillary  vessels, 
and  the  minute  veins  are  often 
visible  in  the  same  tissue.  The 
blood  can  be  seen  entering  the 
field  by  the  arteries,  shooting 
through  them  with  great  rapid- 
ity in  successive  impulses,  and 
flowing  off  more  slowly  by  the 
veins.  In  the  capillary  plexus 
it  moves  with  a  uniform  cur- 
rent, considerably  less  rapid 
than  in  either  the  arteries  or 
the  veins.  A  further  peculi- 
arity of  the  capillary  circula- 
tion is  that  it  has  no  definite 
origin  or  termination,  but  rep- 
resents a  movement  of  the  blood  through  all  parts  of  the  tissue.  Its 
strnims  pass  indifferently  above  and  below,  at  right  angles  to  each 


FIG.  78. 


CAPILLARY  CIRCULATION  in  web  of  frog's  foot. 


THE    CIRCULATION.  301 

other,  or  even  in  opposite  directions ;  penetrating  everywhere  the  sub- 
stance of  the  organ  with  a  kind  of  vascular  irrigation. 

The  motion  of  the  red  and  white  globules  is  also  peculiar,  and  shows 
distinctly  the  difference  in  their  physical  properties.  In  the  larger  ves- 
sels the  red  globules  are  carried  along  in  close  column,  in  the  central 
part  of  the  stream ;  while  near  the  edges  there  is  a  transparent  space 
occupied  by  clear  plasma,  in  which  no  red  globules  are  visible.  In 
the  smaller  vessels  the  globules  pass  two  by  two,  or  follow  each  other 
in  single  file.  Their  flexibility  and  semi-fluidity  are  very  apparent  as 
they  are  folded,  bent  or  twisted,  or  made  to  glide  through  branches  of 
communication,  smaller  than  themselves.  The  white  globules,  on  the 
other  hand,  move  more  slowly.  They  drag  along  the  external  portions 
of  the  current,  and  are  sometimes  arrested  for  a  few  seconds,  adhering 
to  the  inner  surface  of  the  vessel.  Wherever  the  current  is  obstructed 
or  retarded,  the  white  globules  accumulate  and  become  for  the  time 
more  numerous  in  proportion  to  the  red. 

It  is  during  its  passage  through  the  capillaries  that  the  blood  serves 
for  the  nourishment  of  the  tissues,  and  for  absorption,  secretion,  or 
elimination.  The  tenuity  of  the  vascular  walls,  their  extent  of  surface 
in  proportion  to  the  blood  which  they  contain,  and  the  multiplication 
of  the  currents  due  to  their  division  and  inosculation,  all  contribute  to 
this  result,  and  make  these  vessels  the  most  important  physiological 
division  of  the  circulatory  system.  The  nutritious  ingredients  of  the 
blood  transude  through  their  walls,  and  are  appropriated  by  the  tissues 
beyond.  In  the  glandular  organs  they  supply  the  substances  requisite 
for  secretion ;  in  the  villi  of  the  intestine  they  take  up  the  elements  of 
the  digested  food ;  in  the  lungs  they  absorb  oxygen  and  exhale  carbonic 
acid ;  and  in  the  kidneys  they  discharge  the  products  of  destructive 
assimilation,  collected  from  other  parts.  The  capillary  circulation  thus 
furnishes,  directly  or  indirectly,  the  materials  for  the  growth  and 
renovation  of  the  entire  body. 

Physical  Cause  of  the  Capillary  Circulation. — The  conditions 
which  influence  the  movement  of  the  blood  in  the  capillaries  are  some- 
what different  from  those  of  the  arterial  and  venous  circulations.  By 
the  successive  division  of  the  arteries  from  the  heart  outward,  the 
movement  of  pulsation  is  to  a  great  extent  equalized  in  their  smaller 
branches.  But  in  the  neighborhood  of  the  capillary  system,  they  sud- 
denly break  up  into  a  terminal  ramification  of  still  smaller  vessels,  and 
so  lose  themselves  at  last  in  the  capillary  network.  By  this  final  in- 
crease of  the  vascular  surface,  the  equalization  of  the  heart's  action  is 
completed.  There  is  no  longer  any  pulsating  character  in  the  force 
which  acts  on  the  circulating  fluid ;  and  the  blood  moves  through  the 
capillary  vessels  under  a  continuous  and  uniform  pressure. 

This  pressure  is  sufficient  to  propel  the  blood  through  the  capillary 
plexus  into  the  veins.  The  fact  was  first  demonstrated  by  Sharpey, 
who  employed  an  injecting  syringe  with  a  double  nozzle,  one  of  its 
extremities  being  connected  with  a  mercurial  gauge,  while  the  other 


302  TT  NOTIONS    OF    NUTRITION. 

was  inserted  into  the  artery  of  a  recently-killed  animal.  When  ihe 
syringe,  filled  with  defibrinated  blood,  was  fixed  in  this  position,  it 
would  press  with  equal  force  on  the  mercury  in  the  gauge  and  on  the 
fluid  in  the  blood-vessels  ;  and  the  height  of  the  mercurial  column  would 
indicate  the  pressure  required  to  carry  the  blood  through  the  capillaries, 
and  to  return  it  by  the  corresponding  vein.  With  one  end  of  the  in- 
jecting tube  attached  to  the  mesenteric  artery  of  the  dog,  a  pressure 
of  90  millimetres  of  mercury  caused  the  blood  to  pass  through  the  double 
capillary  system  of  the  intestine  and  the  liver;  and  under  a  pressure 
of  130  millimetres,  it  flowed  in  a  full  stream  from  the  extremity  of  the 
vena  cava. 

We  have  obtained  similar  results  by  experimenting  on  the  blood- 
vessels of  the  limbs.  A  full  grown  healthy  dog  was  killed,  and  one 
of  the  hind  legs  immediately  injected  with  defibrinated  blood,  by  the 
femoral  artery,  to  prevent  coagulation  in  the  small  vessels.  A  double 
syringe,  filled  with  defibrinated  blood,  was  then  attached  by  one  of  its 
extremities  to  the  femoral  artery  and  by  the  other  to  a  cardiometer. 
On  making  the  injection,  the  defibrinated  blood  was  returned  from  the 
femoral  vein  in  a  continuous  stream  under  a  pressure  of  120  millimetres, 
and  was  very  freely  discharged  under  a  pressure  of  130  millimetres. 

Since  the  arterial  pressure  during  life  is  equal  to  150  millimetres  of 
mercury,  it  is  evidently  sufficient  to  account  for  the  capillary  circulation. 

The  capillaries  have  also  a  certain  degree  of  elasticity ;  and  they  are 
furthermore  surrounded,  in  many  organs,  by  tissues  which  are  them- 
selves elastic.  The  effect  of  this  property,  in  the  vessels  and  neighbor- 
ing parts,  may  be  seen  in  artificial  injections,  not  only  of  a  lower  limb 
through  the  femoral  artery,  but  also  of  the  liver  through  the  portal 
vein.  If,  while  the  parts  are  distended  by  the  fluid  in  their  vessels,  the 
injecting  force  be  suddenly  arrested,  the  current  does  not  at  once  ce»se, 
but  the  fluid  of  injection  continues  to  escape  for  some  seconds  from  the 
femoral  or  hepatic  vein.  The  elasticity  of  the  surrounding  tissues  sup- 
plements that  of  the  blood-vessels,  and  aids  in  producing  a  uniform 
movement  in  the  capillary  circulation. 

Velocity  of  Blood  in  the  Capillaries. — The  rate  of  movement  in 
the  capillary  circulation  may  be  measured,  with  some  precision,  in  the 
microscopic  examination  of  transparent  tissues.  The  results  obtained 
in  this  way  by  different  observers  (Valentin,  Weber,  and  Volkmann), 
show  that  the  rate  of  movement  of  the  blood  through  the  capillaries 
is  rather  less  than  one  millimetre  per  second.  Since  the  rapidity  of 
the  current  must  be  in  inverse  ratio  to  the  calibre  of  the  vessels  through 
which  it  moves,  it  appears  that  the  united  calibre  of  all  the  capillaries 
must  be  not  less  than  300  times  invater  than  that  of  the  arteries.  It 
docs  not  follow  from  this  that  the  whole  quantity  of  blood  contained 
in  the  capillaries  at  any  given  time  is  greater  than  that  in  the  arteries; 
since,  although  the  united  calibre  of  the  capillaries  is  large,  their  Icixjlh 
is  very  small.  The  structure  of  the  capillary  system  is  such  as  to  dis- 
seminate a  small  quantity  of  blood  over  a  large  space,  allowing  its 


THE    CIRCULATION.  803 

physiological  reactions  to  take  place  with  rapidity  and  .energy.  Al- 
though the  movement  of  the  blood  in  these  vessels,  accordingly,  is 
slow,  yet  as  the  distance  between  the  arteries  and  the  veins  is  very 
small,  it  requires  but  a  short  time  for  the  blood  to  traverse  the  capillary 
system,  and  commence  its  returning  passage  by  the  veins. 

General  Rapidity  of  the  Circulation. 

The  rapidity  with  which  the  blood  passes  through  the  entire  round 
of  the  circulation  has  been  demonstrated  by  Hering,  Poisseuille, 
Matteucci,  and  Vierordt  in  the  following  manner :  A  solution  of  potas- 
sium ferrocyanide  was  injected  into  the  right  jugular  vein  of  the  horse, 
at  the  same  time  that  a  ligature  was  placed  on  the  corresponding  vein 
of  the  opposite  side,  and  an  opening  made  in  it  above  the  ligature.  The 
blood  flowing  from  this  opening  was  received  in  separate  vessels,  at 
intervals  of  five  seconds,  and  afterward  examined.  The  blood  drawn 
from  the  first  to  the  twentieth  second  contained  no  trace  of  the  ferro- 
cyanide ;  but  that  which  escaped  from  the  twentieth  to  the  twenty-fifth 
second  showed  unmistakable  evidence  of  its  presence.  During  this 
time  therefore  the  foreign  salt  must  have  passed  from  the  point  of  in- 
jection to  the  right  side  of  the  heart,  thence  through  the  pulmonary 
circulation  to  the  left  side  of  the  heart,  outward  by  the  arteries  to 
the  capillaries  of  the  head  and  neck,  and  thence  down  toward  the  heart 
by  the  opposite  jugular  vein. 

Further  observations  have  shown  that  the  duration  of  the  circulatory 
movement  varies  somewhat  in  different  animals ;  being,  as  a  general 
rule,  longer  in  those  of  larger  size.  Their  main  result,  as  given  by 
Milne  Edwards,*  is  as  follows: 

DUKATION    OF   THE    ClKOULATORY    MOVEMENT. 

In  the  Horse 28  seconds. 

"       Dog .  15       " 

a       Goat 13       " 

"       Rubbit .      T       " 

In  experimenting  on  the  dog,  by  injecting  a  solution  of  potassium 
ferrocyanide  into  the  jugular  vein,  and  immediately  drawing  blood 
from  the  corresponding  vein  on  the  opposite  side,  we  have  found  that 
the  short  time  required  for  closing  the  first  vein  by  ligature  after  mak- 
ing the  injection,  and  opening  the  second  to  obtain  a  specimen  of  blood, 
is  sufficient  for  the  passage  of  the  ferrocyanide.  If  we  regard  the 
duration  of  this  movement  in  man  as  intermediate  between  that  in  the 
dog  and  the  horse,  according  to  the  difference  in  size,  this  would  give 
the  time  required  by  the  blood  to  make  the  complete  circuit  of  the 
vascular  system  as  not  far  from  20  seconds. 


*  Le9ons  sur  la  Physiologie.     Paris,  1859,  tome  iv.,  p.  364. 


304 


FUNCTIONS    OF    NUTRITION. 


Fio.79. 


Local  Variations  in  the  Capillary  Circulation. 

An  important  class  of  phenomena  connected  with  the  capillary  cir- 
culation consists  of  its  local   variations.     These  variations  are  often 

very  marked,  and  show  themselves  in 
many  different  parts  of  the  body.  The 
pallor  or  suffusion  of  the  face  from  men- 
tal emotion,  the  congestion  of  the  glands 
and  mucous  membranes  during  diges- 
tion, and  the  denned  redness  of  the  skin 
after  irritating  applications,  are  instances 
of  this  kind.  They  are  due  to  the  vary- 
ing condition  of  the  smaller  arterial 
branches  which  contract  or  dilate  after 
different  nervous  influences,  and  thus 
diminish  or  increase  the  quantity  of 
blood  in  the  capillary  circulation.  When 
contracted,  they  resist  the  impulse  of  the 
arterial  current,  and  admit  the  blood  in 
smaller  quantity.  When  dilated,  they 
allow  it  a  free  access,  and  the  blood 
passes  in  greater  abundance  to  the 
capillary  vessels. 

These  changes  are  most  distinctly 
manifested  in  the  periodical  congestion 
of  the  glandular  organs.  All  the  glands 
and  mucous  membranes  of  the  digestive 
apparatus  enter  into  a  state  of  vascular 
excitement  at  the  time  of  secretion  and 
digestion.  This  unusual  vascularity  can 
be  seen,  in  the  living  animal,  in  the 
pancreas,  and  in  the  mucous  membranes 
of  the  stomach  and  small  intestine; 
which  are  visibly  redder  and  more  turgid 
during  digestion  and  absorption  than  in 
the  fasting  condition. 

The  variations  of  the  capillary  circu- 
lation, as  influenced  by  glandular  activ- 
ity and  repose,  have  been  most  success- 
fully studied  in  the  submaxillary  gland 
of  the  dog.  While  this  gland  is  in  ac- 
tive secretion  the  quantity  of  blood  pass- 
ing through  its  vessels  is  largely  in- 
creased. In  the  experiments  of  Ber- 
nard* the  submaxillary  vein,  during 
the  condition  of  glandular  repose,  yielded 
five  cubic  centimetres  of  blood  in  a  little  more  than  one  minute;  but 


DIAGRAM    OF    TIIK    CIRCULATION.— 1. 

Heart.  J.  Lmi^.  :;.  Mead  ami  upper 
extivmitirs.  1.  Spl.-i'ii.  ;").  I  nt.  Clitic. 
(I.  Kidney.  7.  Lower  extremities.  8. 


;:  Lrrons  stir  Irs  LiqiiuU-s  dc  l'<  h 


Paris,  1859,  tome  ii.,  p.  "27'2 


THE    CIRCULATION.  305 

when  the  organ  was  excited  to  functional  activity,  it  discharged  the 
same  quantity  in  fifteen  seconds.  Thus  the  volume  of  blood  passing 
through  the  gland  in  a  given  time  was  more  than  four  times  as  great 
while  in  active  secretion  as  in  a  condition  of  repose. 

The  increased  flow  of  blood,  in  a  secreting  gland,  is  accompanied  by 
in  important  change  in  its  appearance.  During  repose,  the  blood, 
which  enters  the  submaxillary  gland  bright  red,  is  changed  from 
arterial  to  venous,  and  passes  out  by  the  veins  of  a  dark  color.  But 
during  active  secretion,  the  blood  is  not  only  discharged  in  larger 
quantity,  but  passes  out  by  the  veins  of  a  red  color,  hardly  distin- 
guishable from  that  of  arterial  blood.  When  the  secretion  of  the 
gland  is  suspended,  its  venous  blood  again  becomes  dark-colored  as 
before.  There  is  little  doubt  that  the  same  is  true  of  other  glands,  and 
that  the  blood  circulating  in  their  capillaries  is  changed  from  red  to 
blue  only  during  the  period  of  functional  repose ;  while  at  the  time  of 
active  secretion  it  passes  through  the  vessels  in  greater  abundance,  and 
retains  its  ruddy  color  in  the  veins. 

This  variation  depends  on  the  different  functions  performed  by  the 
blood  in  the  two  periods.  During  glandular  repose  it  serves  for  the 
usual  changes  of  nutrition,  which  consume  its  oxygen,  and  conse- 
quently change  its  color  from  red  to  blue.  But  during  active  secretion 
the  blood  passes  in  larger  quantity,  while  its  watery  and  saline  ingre- 
dients exude  into  the  secretory  ducts,  bringing  with  them  the  materials 
accumulated  in  the  intervals  of  repose ;  and  as  there  is  nothing  in  this 
process  to  exhaust  the  oxygen  of  the  blood,  it  therefore  passes  out  by 
the  veins  with  its  color  comparatively  unaltered. 

A  similar  ruddy  color  of  the  blood  is  to  be  seen  in  the  renal  veins, 
where  it  is  often  nearly  identical  with  that  of  arterial  blood.  When 
the  kidneys  are  in  a  state  of  functional  activity,  the  difference  in  color 
between  the  renal  veins  and  those  of  the  neighboring  muscles,  or  the 
vena  cava,  is  very  marked.  The  only  important  change  in  the  blood 
while  passing  through  the  kidneys  is  the  elimination  of  its  urea ;  the 
process  of  local  nutrition  being  altogether  secondary.  Consequently 
the  blood  loses  but  little  oxygen  in  these  organs,  and  suffers  but  little 
alteration  of  its  hue.  ' 

On  the  other  hand,  the  venous  blood  coming  from  the  muscles  is 
very  dark,  especially  if  they  be  in  a  state  of  active  contraction ;  and 
as  the  muscles  form  so  large  a  part  of  the  mass  of  the  body,  their  con- 
dition has  a  preponderating  influence  on  the  color  of  the  venous  blood 
in  general.  The  greater  the  activity  of  the  muscular  system,  the 
darker  is  the  blood  returning  from  the  trunk  and  extremities.  In  a 
state  of  repose  or  paralysis,  on  the  contrary,  the  change  is  less  marked ; 
and  in  the  complete  relaxation  produced  by  abundant  hemorrhage  or 
profound  etherization,  the  blood  in  the  larger  veins  often  approximates 
in  color  to  that  in  the  arteries. 

Finally,  in  the  lungs  the  reverse  process  takes  place.  In  these  organs 
the  blood  is  supplied  with  a  fresh  quantity  of  oxygen,  to  replace  that 

U 


306  FUNCTIONS    OF    NUTRITION. 

consumed  elsewhere ;  and  accordingly  it  changes  its  color  from  dark 
purple  to  bright  red  while  passing  through  the  pulmonary  capillaries. 

Both  the  simpler  and  the  more  important  phenomena  of  the  circu- 
lation vary  therefore  at  different  times  and  in  different  organs.  The 
blood  has  a  different  composition  as  it  returns  from  different  parts, 
or  has  been  employed  in  different  functions.  In  the  parotid  gland  it 
yields  the  ingredients  of  the  saliva ;  in  the  kidneys  those  of  the  urine. 
In  the  portal  vein  it  contains  the  products  of  intestinal  digestion  ;  and 
in  the  hepatic  vein  it  has  suffered  a  further  alteration  by  passing 
through  the  capillaries  of  the  liver.  .  In  the  lungs  it  changes  from  blue 
to  red,  and  in  the  greater  part  of  the  general  system,  from  red  to 
blue ;  and  even  its  temperature  varies  in  different  veins,  according  to 
the  special  nutritive  changes  in  the  organs  from  which  they  come. 


CHAPTER  VII. 
THE  LYMPHATIC  SYSTEM. 

IN  addition  to  the  series  of  connected  canals,  through  which  the 
blood  passes  in  a  continuous  round  by  the  arteries,  capillaries,  and 
veins,  there  is  also  a  system  of  vessels,  leading  from  the  periphery 
toward  the  centre,  and  discharging  into  the  great  veins  near  the  heart 
the  materials  which  have  been  absorbed  from  the  tissues.  The  fluid 
in  these  vessels  is  nearly  colorless,  and  from  its  transparent  and 
watery  appearance  is  called  the  "lymph,"  the  vessels  themselves 
constituting  the  lymphatic  system. 

As  the  blood  moves  through  the  capillaries  under  the  influence  of 
the  arterial  pressure,  certain  of  its  ingredients  transude  through  the 
vascular  walls  and  penetrate  the  interstices  of  the  tissues.  An  in- 
creased pressure  of  the  blood,  either  from  arterial  congestion  or  from 
obstruction  to  the  venous  current,  will  increase  the  amount  of  transu- 
dation,  producing  an  oedematous  condition,  which  is  first  perceptible  in 
the  loose  connective  tissue,  but  which  may  afterward  involve  the  more 
compact  substance  of  the  organs.  In  the  normal  state  of  the  circula- 
tion, this  interstitial  fluid,  which  is  the  source  of  nutriment  for  the 
solid  parts,  is  renewed  by  continual  change.  As  fresh  supplies  are 
drawn  from  the  circulating  blood,  the  older  portions  are  removed  by 
absorption  and  returned  to  the  centre  of  the  circulation  by  the  lym- 
phatic vessels.  Thus  these  vessels  may  be  considered  as  complementary 
in  function  to  the  veins.  The  blood,  containing  the  red  globules,  is 
rapidly  returned  to  the  lungs  by  the  veins,  to  regain  the  necessary 
oxygen ;  while  the  lymphatic  vessels  collect  more  gradually  the  fluids 
which  have  served  for  nutrition  and  growth. 

General  Structure  and  Arrangement  of  the  Lymphatic  System. 
In  structure  the  lymphatics  do  not  essentially  differ  from  the  blood- 
vessels, their  main  peculiarity  being  the  greater  delicacy  and  trans- 
parency of  their  walls.  Those  of  larger  and  medium  size  .consist  of 
three  coats,  similar  in  general  character  to  the  corresponding  tunics 
of  the  blood-vessels.  According  to  Kolliker,  the  external  coat  alone 
is  distinguished  from  that  of  the  veins  by  the  presence  of  muscular 
fibres  arranged  in  a  longitudinal  and  oblique  direction ;  as  seen  in 
lymphatics  of  0.2  millimetre  in  diameter  and  upward.  Like  the  veins, 
they  are  provided  with  numerous  valves,  opening  toward  the  heart 
and  closing  toward  the  periphery.  The  smallest  lymphatic  vessels 
have  only  a  single  coat,  composed  of  flattened,  epithelium-like,  nucleated 

307 


308  FUNCTIONS    OF     NUTRITION. 

cells,  which  may  be  brought  into  view,  like  those  of  the  capillary  blood- 
vessels, by  the  staining  action  of  silver  nitrate. 

Origin  and  Course  of  the  Lymphatic  Vessels. — So  far  as  the  origin 
of  the  lymphatic  vessels  has  been  demonstrated  by  injections,  they 
commence  by  irregular  plexuses.  They  are  more  abundant  in  organs 
which  are  well  supplied  with  blood-vessels,  and  are  absent  in  non- 
vascular  tissues,  such  as  those  of  the  cornea,  the  vitreous  body,  and 
the  epidermic  and  epithelial  layers  of  the  skin  and  mucous  membranes. 
According  to  Recklinghausen,  the  meshes  of  the  lymphatic  plexus  are 
usually  intercalated  between  those  of  the  capillary  blood-vessels;  so 
that  the  point  of  junction  of  two  or  more  lymphatics  is  in  the  mid- 
dle of  the  space  surrounded  by  the  adjacent  blood-vessels.  Thus  the 
lymphatic  capillary  is  situated  at  the  greatest  possible  distance  from 
the  nearest  capillary  blood-vessels ;  and  in  the  transudation  of  fluids 
from  one  to  the  other,  the  intervening  tissue  is  completely  traversed 
by  the  nutritious  ingredients  of  the  blood.  In  membranous  expan- 
sions presenting  a  free  surface,  as  in  the  skin  and  onucous  membranes, 
the  capillary  blood-vessels  are  situated  near  the  surface,  while  the 
lymphatics  occupy  a  deeper  plane.  In  the  villi  of  the  intestine,  the 
network  of  blood-vessels  is  immediately  beneath  the  epithelial  layer, 
and  the  lacteal  vessel  in  the  central  part  of  the  villus. 

Beside  the  lymphatic  capillaries  proper,  certain  irregularly-shaped 
spaces  or  canals,  containing  a  colorless  serous  fluid,  have  been  found 
in  organs  composed  of  dense  connective  tissue,  like  the  central  tendon 
of  the  diaphragm  and  muscular  fasciae.  They  are  generally  demon- 
strated by  treating  the  tissues  with  silver  nitrate,  which  stains  the  solid 
portions  of  a  dark  color,  but  leaves  the  capillary  vessels  and  serous 
canals  uncolored.  These  interstitial  canaliculi  are  regarded  by  some 
observers  as  continuous  with  the  lymphatic  capillaries,  and  as  the 
immediate  sources  of  supply  for  the  lymph.  They  ar^e  distinguished 
from  the  lymphatic  capillaries  by  their  smaller  size,  and  by  the  fact 
that  they  are  not  provided  with  an  epithelial  lining. 

From  their  plexuses  of  origin  the  lymphatic  vessels  pass  inward 
to  the  great  cavities  of  the  body,  uniting  into  branches  and  trunks, 
and  following  generally  the  course  of  the  principal  blood-vessels. 
Those  of  the  lower  extremities  enter  the  abdomen  and  join  the  abdomi- 
nal lymphatics,  to  form  the  commencement  of  the  thoracic  duct.  This 
duct  ascends,  through  the  chest,  to  the  root  of  the  neck,  where  it  is 
joined  by  lymphatics  from  the  left  side  of  the  head  and  the  left  upper 
extremity,  and  terminates  in  the  left  subclavian  vein,  at  its  junction 
with  the  left  internal  jugular.  The  lymphatic  vessels  coming  from  the 
right  side  of  the  head  and  neck  and  the  right  upper  extremity  form  the 
right  lymphatic  duct,  which  terminates  in  the  right  subclavian  vein 
at  its  junction  with  the  right  internal  jugular.  Thus  the  lymph, 
collected  from  the  vascular  tissues  of  the  entire  body,  is  mingled  with 
the  venous  blood  a  little  before  its  arrival  at  the  right  side  of  the  heart. 

The  Great  Serous  Cavities  are  Lymphatic  Lacunae. — In  the  am- 


THE    LYMPHATIC    SYSTEM.  309 

phibious  reptiles  there  are  irregularly-shaped  spaces  or  lacuna,  forming 
part  of  the  lymphatic  system  and  interposed  between  adjacent  organs 
in  various  parts  of  the  body..  In  the  mammalia  the  peritoneal  and 
pleural  cavities,  and  probably  all  the  principal  serous  sacs,  are  also  in 
communication  with  the  lymphatic  vessels.  This  was  first  shown  by 
Recklinghausen  *  in  the  rabbit,  by  injecting  the  peritoneal  cavity  with 
milk,  or  a  watery  fluid  holding  granules  of  coloring  matter  in  suspen- 
sion, after  which  the  lymphatic  vessels  of  the  central  tendon  of  the 
diaphragm  were  found  filled  with  the  injection.  Furthermore,  the 
central  tendon  of  the  diaphragm  being  removed  from  the  recently- 
killed  animal,  and  a  drop  of  milk  placed  upon  its  peritoneal  surface, 
the  milk  globules  could  be  observed  under  the  microscope,  running 
in  converging  currents  to  certain  points  on  the  surface  of  the  tendon 
and  thence  penetrating  into  its  lymphatic  vessels.  The  cavity  of  the 
pleura  has  been  found  by  similar  means  to  communicate  with  the  lym- 
phatic vessels  in  its  neighborhood.  The  serous  cavities  accordingly 
are  either  extensive  lacunaB,  forming  in  some  regions  the  origin  of 
the  lymphatics,  or  else  they  are  wide  and  shallow  expansions,  situated 
at  various  points  in  the  course  of  these  vessels. 

The  Lymphatic  Glands. — During  the  passage  of  the  lymphatic  ves- 
sels from  the  periphery  toward  the  centre,  they  are  repeatedly  inter- 
rupted by  ovoidal  gland-like  bodies,  of  a  pale  reddish  color,  varying,  in 
man,  from  two  to  twenty  millimetres  in  their  long  diameter.  They  do 
not  exist  in  fish  and  reptiles,  but  are  always  present  in  birds  and  mam- 
malia. As  a  rule,  each  gland  receives  several  lymphatic  vessels,  com- 
ing from  the  periphery  ;  and  several  others  leave  it  at  the  opposite  sur- 
face, continuing  their  course  toward  the  centre  of  the  circulation.  The 
former  are  called  the  "afferent,"  the  latter  the  "efferent"  lymphatic 
vessels.  The  lymphatic  glands  have  no  excretory  duct,  and  whatever 
new  materials  they  produce  must  be  carried  away  either  by  the  veins 
or  by  the  efferent  lymphatic  vessels. 

The  lymphatic  glands  consist,  first,  of  an  external  fibrous  envelope, 
with  prolongations  from  its  internal  surface  in  the  form  of  septa  and 
branching  bands,  dividing  the  interior  into  smaller  spaces  by  their  inos^ 
culation.  The  fibrous  bands  composing  this  framework  are  the  "trabee- 
ulae."  Secondly,  in  the  interstices  between  the  trabeculae  is  contained 
the  pulpy  substance  of  the  gland.  Thirdly,  the  blood-vessels  in  the 
interior  of  the  gland  follow  distinct  routes  in  the  spaces  between  the 
trabeculae.  They  are  surrounded  and  held  in  position  by  fine  branch- 
ing fibres  attached  to  their  external  surface;  and  in  the  meshes  of 
these  fibres,  as  well  as  between  the  blood-vessels,  are  imbedded  a  great 
number  of  rounded,  granular,  nucleated  cells,  about  9  mmm.  in  diam- 
eter, similar  to  the  white  globules  of  the  blood  and  lymph,  and  known 
in  this  situation  as  "lymph  globules."  The  presence  of  these  cells, 
between  and  immediately  around  the  capillary  blood-vessels,  gives  to 


Strieker's  Manual  of  Histology,  Buck's  Edition.     New  York,  1872,  p.  221. 


310  FUNCTIONS    OF    NUTRITION. 

the  parts  occupied  by  them  a  well-marked  opaque  appearance  ;  and  they 
thus  form,  in  a  thin  section  of  the  glaud,  elongated,  opaque  tracts, 
separated  by  transparent  interspaces,  pud  communicating  with  each 
other  at  frequent  intervals.  These  tracts  are  called  the  medullary  cords 
of  the  lymphatic  gland.  They  are  the  only  vascular  parts  of  the  organ  ; 
as  the  capillary  blood-vessels  never  pass  beyond  them  into  the  inter- 
vening transparent  spaces.  The  transparent  spaces  are  the  lymph- 
paths,  or  the  channels  by  which  the  lymph  traverses  the  gland  from 
its  afferent  to  its  efferent  vessels.  The  afferent  lymphatic  vessels, 
according  to  the  testimony  of  nearly  all  observers,  after  ramifying 
upon  the  outer  surface  of  the  gland,  penetrate  its  fibrous  envelope 
and  become  continuous  with  the  transparent  portions  of  its  substance. 
This  is  shown  by  injections  of  the  gland  from  the  afferent  vessels; 
and  Kolliker  has  demonstrated  a  connection  of  the  same  channels 
with  the  efferent  vessels,  by  injecting  them  from  the  substance  of  the 
gland. 

The  cause  of  the  transparent  appearance  presented  by  the  lymph- 
paths  in  thin  sections  of  the  gland  is  that  their  lymph-cells  are  easily 
detached  by  manipulation,  while  those  of  the  medullary  cords  are  more 
firmly  fixed  in  the  fibrous  mesh-work  and  do  not  so  readily  yield  to  a 
displacing  force.  It  has  been  found  by  Kolliker  that  a  watery  or 
serous  fluid,  injected  through  the  substance  of  the  gland  under  mod- 
erate pressure,  will  also  displace  these  cells  and  leave  the  parts 
which  they  occupied  nearly  clear.  It  is  for  this  reason  that  the 
lighter  spaces  in  the  lymphatic  glands  are  regarded  as  the  chan- 
nels by  which  the  lymph  passes  from  the  afferent  to  the  efferent 
vessels,  the  lymph-cells  being  detached  by  this  current  from  their 
place  of  growth  and  carried  onward  through  the  lymphatic  system. 

Transudation  and  Absorption  by  Animal  Tissues. 

If  a  fresh  animal  membrane  be  securely  fastened  over  the  lower 
end  of  a  glass  tube,  the  tube  filled  with  a  solution  of  various  sub- 
stances, and  immersed  in  an  exterior  vessel  of  pure  water,  so  that  the 
membrane  is  a  diaphragm,  with  the  water  on  one  side  and  the  solution 
on  the  other,  it  is  found  that  different  substances  penetrate  the  mem- 
brane and  pass  through  it  to  the  water  with  different  degrees  of  rapidity. 
As  a  rule  crystallizable  substances,  such  as  mineral  salts,  glucose,  or 
urea,  pass  with  facility ;  while  non-crystallizable  matters,  such  as  albu- 
men, starch,  or  gum,  pass  either  not  at  all,  or  with  difficulty.  The 
former  are  called  "diffusible"  substances,  because  they  pass  through 
the  membrane  and  become  diffused  in  the  water  beyond;  the  latter 
are  "  non-diffusible,"  and  do  not  appear  in  the  exterior  liquid,  which 
consequently  maintains  its  purity.  This  distinction  is  not  absolute, 
since  nearly  all  soluble  substances  may  be  made  to  transude  in  SOUK- 
decree  by  increasing  the  pressure  on  the  corresponding  side  of  the 
membrane ;  but  the  difference  in  this  respect  is  often  very  great. 


THE    LYMPHATIC    SYSTEM.  311 

According  to  Liebig,*  the  requisite  pressure  for  different  liquids,  passing 
through  the  same  membrane  in  a  given  time,  is  as  follows : 

PRESSURE  REQUIRED  TO  CAUSE  TRANSUDATION  THROUGH  OX-BLADDER. 

Kind  of  liquid.  Height  of  the  mercurial  column. 

Water       .    ^ 320  millimetres. 

Solution  of  salt 530          " 

Oil 906          " 

Alcohol 1280          " 

The  different  diffusibility  of  different  substances  has  been  employed 
for  separating  them  from  each  other,  when  mingled  in  the  same  solution. 
This  process  is  termed  Dialysis.  If  a  solution  containing  both  gum 
and  sugar  be  placed  on  one  side  of  a  membranous  diaphragm,  with 
pure  water  on  the  other,  the  sugar  will  pass  through,  while  the  gum 
will  be  left  behind.  If  a  mixture  of  albumen  and  sodium  chloride  be 
placed  under  the  same  conditions,  the  salt  will  transude  leaving  the 
albumen  by  itself;  the  two  substances  being  thus  separated  by  the 
action  of  the  membrane.  By  this  means  poisonous  crystallizable  matters 
may  be  extricated  from  organic  mixtures  in  sufficient  purity  for  their 
detection  by  chemical  tests ;  and  on  the  other  hand  albuminous  matters 
may  be  purified  from  the  saline  ingredients  of  the  animal  fluids,  and 
obtained  in  a  condition  for  examination  and  analysis. 

Endosmosis  and  Exosmosis. — Beside  the  elimination  of  chemical 
ingredients,  as  above  described,  transudation  often  gives  rise  to  a  change 
in  volume  of  the  fluids  on  either  side  of  the  membrane.  When  a  mem- 
brane is  interposed  between  two  liquids  which  are  transmitted  with 
different  degrees  of  facility,  that  which  passes  most  readily  will  accu- 
mulate on  the  opposite  side  of  the  membrane. 

If,  for  example,  a  solution  of  salt  and  an  equal  volume  of  distilled 
water  be  placed  in  contact  with  opposite  sides  of  the  membrane,  after 
a  time  they  will  have  become  mingled,  to  some  extent,  with  each  other. 
A  part  of  the  salt  will  have  passed  into  the  water,  giving  it  a  saline 
taste  ;  and  a  part  of  the  water  will  have  passed  into  the  saline  solution, 
making  it  more  dilute  than  before.  If  the  quantities  of  the  two 
liquids  be  now  measured,  it  will  be  found  that  a  comparatively  large 
quantity  of  water  has  passed  into  the  saline  solution,  and  a  compara- 
tively small  quantity  of  the  saline  solution  has  passed  into  the  water. 
That  is,  the  water  passes  inward  to  the  salt  more  rapidly  than  the 
salt  passes  outward  to  the  water.  The  consequence  is,  that  the  volume 
of  the  saline  solution  is  increased,  while  that  of  the  water  is  dimin- 
ished. The  more  abundant  passage  of  the  water,  through  the  membrane 
to  the  salt,  is  called  endosmosis;  and  the  more  scanty  passage  of  the  salt 
outward  to  the  water  is  called  exosmosis. 

The  mode  usually  adopted  for  measuring  the  rapidity  of  endosmosis 
is  to  take  a  glass  vessel,  wide  at  the  bottom  and  narrow  at  the  top, 
with  a  membrane  stretched  over  its  larger  orifice  and  secured  by  a 

*  Annales  de  Chimie  et  de  Physique.    Paris,  1849,  tome  xxv.,  p.  373. 


312  FUNCTIONS    OF    NUTRITION. 

ligature.  To  its  top  there  is  fitted  a  narrow  upright  glass  tube,  open 
at  both  ends.  The  instrument  thus  prepared  is  filled  with  a  saline  or 
organic  solution  and  placed  in  distilled  water ;  so  that  the  membrane, 
stretched  over  its  mouth,  shall  be  in  contact  with  water  on  one  side  and 
with  the  interior  solution  on  the  other.  As  the  water  then  passes  in 
by  endosmosis  faster  than  the  ingredients  of  the  solution  pass  out,  an 
accumulation  takes  place  within  the  vessel,  and  the  fluid  rises  in  the 
upright  tube.  The  height  to  which  it  thus  rises  in  a  given  time  is  a 
measure  of  the  intensity  of  the  endosmosis,  and  of  its  excess  over 
exosmosis.  Such  an  instrument  is  called  an  endosmometer. 

Physical  Conditions  influencing  Endosmosis. — The  conditions  which 
regulate  the  rapidity  and  extent  of  endosmosis  have  been  investigated 
by  Dutrochet,*  Graham,  Vierordt,  Matteucci,  and  Cima.  The  first  of 
these  conditions  is  the  freshness  of  the  animal  membrane.  A  mem- 
brane which  has  been  dried  and  remoistened,  or  which  has  lost  its 
freshness  from  any  cause,  will  not  produce  its  full  effect.  If  the  mem- 
brane be  allowed  to  remain  and  macerate  in  the  fluids,  the  endosmotic 
column,  after  rising  to  a  certain  height,  begins  to  descend  when  putre- 
faction commences,  and  the  two  liquids  finally  sink  to  the  same  level. 

The  next  condition  is  the  extent  of  contact  between  the  membrane 
and  the  liquids.  The  greater  this  extent,  the  more  rapid  is  endosmosis. 
An  endosmometer  with  a  wide  mouth  will  produce  more  effect  than 
with  a  narrow  one,  though  the  volume  of  liquid  may  be  the  same. 
The  action  which  takes  place  in  the  membrane  is  proportional  to  its 
extent  of  surface. 

The  nature  of  the  membrane  employed,  and  even  its  position  in  re- 
gard to  the  two  liquids,  also  influence  the  result.  Different  membranes 
act  with  different  degrees  of  force,  since  the  power  of  absorption  for 
a  given  liquid  varies  with  different  tissues.  In  the  experiments  of 
Chevreul,f  definite  quantities  of  various  animal  tissues  were  immersed 
in  different  liquids  for  twenty-four  hours ;  at  the  end  of  which  time 
their  increase  in  weight  showed  the  quantity  of  liquid  absorbed.  The 
result  is  given  in  the  following  table : 

COMPARATIVE  POWER  OF  ABSORPTION  IN  DIFFERENT  TISSUES. 
100  Parts  of  Water.        Saline  Solution.          Oil. 


Cartilage, 

Tendon, 

Elastic  ligament, 

Cornea, 

Cartilaginous  ligament, 

Dried  fibrine, 


absorb  in 
24  hours, 


231  parts.  125  parts. 

178      "  114      u  8.6  parts. 

148      "  30      "  7.2      u 

461      "  370      "  9.1      " 

319      "  3.2      " 

301      "  151      " 


Thus  the  tissue  of  cartilage  will  absorb,  weight  for  weight,  nearly 
30  per  cent,  more  water  than  that  of  the  tendons ;  and  the  cornea  will 
absorb  nearly  twice  as  much  as  cartilage.  The  animal  tissues  in  general 

*  Nouvelles  Recherches  sur  I'EndomiOte  et  1'Exosmose.     Paris,  1828. 
f  In  Longet.  TraitS  de  Physiologic.     Paris,  1861,  tome  i.,  p.  383. 


THE    LYMPHATIC    SYSTEM.  313 

absorb  water  more  abundantly  than  a  saline  solution  ;  and  if  a  partially 
dried  membrane  be  placed  in  a  saturated  solution  of  sodium  chloride, 
owing  to  its  rapid  absorption  of  the  water,  a  part  of  the  salt  will  be 
left  behind  and  deposited  in  a  crystalline  form  on  its  surface. 

The  position  of  the  membrane  exerts  a  similar  influence,  owing  to 
a  difference  of  absorbing  power  in  its  two  surfaces.  Matteucci  found 
that,  in  using  the  mucous  membrane  of  the  ox-bladder  with  water  and 
a  solution  of  sugar,  if  the  mucous  surface  of  the  membrane  were  in 
contact  with  the  saccharine  solution,  the  liquid  rose  in  the  endosmome- 
ter  between  80  and  113  millimetres  in  two  hours.  But  if  the  same 
surface  were  turned  toward  the  water,  the  rise  of  the  column  of  fluid 
was  only  between  63  and  72  millimetres  in  the  same  time. 

Another  important  condition  is  the  constitution  of  the  two  liquids 
and  their  relation  to  each  other.  Dutrochet  measured  the  force  with 
which  water  passes  through  the  mucous  membrane  of  the  ox-bladder, 
into  different  solutions  of  similar  density,  with  the  following  result :  * 

ENDOSMOSIS  OF  WATER  TOWARD  DIFFERENT  LIQUIDS. 
With  solution  of  Intensity  of  endosmosis. 

Gelatine 3 

Gum 5 

Sugar 11 

Albumen 12 

As  a  general  rule,  when  the  liquids  employed  are  water  and  a  saline 
solution,  the  more  concentrated  the  solution,  the  more  active  is  endos- 
mosis ;  a  larger  quantity  of  water  passing  toward  a  denser  liquid  than 
toward  one  which  is  more  dilute.  But  the  above  table  shows  that 
endosmosis  will  vary  in  activity  with  solutions  of  different  substances, 
even  though  they  may  be  of  the  same  density ;  and  when  the  two 
liquids  used  are  alcohol  and  water,  endosmosis  takes  place  from  the 
water  to  the  alcohol,  that  is,  from  the  denser  liquid  to  the  lighter. 

When  two  different  liquids,  therefore,  are  placed  in  contact  with  the 
membrane,  there  is  usually  a  comparatively  rapid  endosmosis  in  one 
direction  and  a  comparatively  slow  exosmosis  in  the  other,  according 
to  the  rates  at  which  the  two  liquids  traverse  the  membrane.  But  in 
some  cases  there  may  be  endosmosis  without  exosmosis.  Thus  when 
water  and  albumen  are  employed  as  the  two  liquids,  while  the  .water 
readily  passes  inward  through  the  membrane,  the  albumen  does  not 
pass  out.  If  an  opening  be  made  in  the  large  end  of  a  fowl's  egg,  so 
as  to  expose  the  shell-membrane,  and  the  whole  immersed  in  water, 
endosmosis  will  take  place  freely  from  the  water  to  the  albumen,  so  as 
to  distend  the  membrane  and  make  it  protrude,  like  a  hernia,  from  the 
opening  in  the  shell.  But  the  albumen  does  not  pass  outward,  and 
the  water  remains  pure.  After  a  time  the  pressure  from  within,  due 
to  the  accumulation  of  fluid,  becomes  sufficient  to  burst  the  shell- 
membrane,  after  which  the  two  liquids  mingle  with  each  other. 

*  In  Matteucci,  Physical  Phenomena  of  Living  Beings.  Pereira's  Translation. 
Philadelphia,  1848,  p.  48. 


314  FUNCTIONS    OF    NUTRITION. 

But  a  substance  like  albumen,  which  will  not  pass  out  by  exosmosis 
toward  pure  water,  may  traverse  a  membrane  which  is  in  contact  with 
a  solution  of  salt.  This  has  been  shown  with  the  shell-membrane  of 
the  fowl's  egg,  which,  if  immersed  in  a  watery  solution  containing  3  or 
4  per  cent,  of  sodium  chloride,  will  allow  the  escape  of  a  small  proportion 
of  albumen.  If  a  mixed  solution  of  albumen  and  salt  be  placed  in  a 
dialysing  apparatus,  at  first  the  salt  alone  will  pass  outward,  leaving 
the  albumen  behind  ;  but  after  the  exterior  liquid  has  become  perceptibly 
saline,  the  albumen  also  begins  to  transude  in  appreciable  quantity. 

The  continuance  of  endosmosis  is  favored  by  renewal  of  the  two 
liquids.  Since  the  accumulation  of  fluid  on  one  side  of  the  membrane 
depends  on  the  difference  in  composition  of  the  liquids  employed,  when 
the  process  has  continued  for  some  time,  and  the  two  liquids  have 
approximated  each  other  in  composition,  the  activity  of  endosmosis 
is  diminished  in  a  corresponding  degree.  But  if  the  exterior  liquid  be 
replaced  by  pure  water,  and  the  interior  solution  maintained  at  its 
original  strength  by  the  addition  of  new  ingredients,  transudation  will 
go  on  with  undiminished  activity  so  long  as  the  membrane  retains  its 
absorbent  power.  The  effect  of  a  continuous  current  in  aiding  endos- 
mosis may  be  shown  by  filling  the  cleansed  intestine  of  a  rabbit  with 
water  from  a  reservoir  and  then  placing  it  in  a  shallow  vessel  containing 
a  dilute  solution  of  hydrochloric  acid.  If  the  water  be  allowed  to  flow 
through  the  intestine  under  pressure  from  the  reservoir,  that  which  is 
discharged  from  its  open  extremity  will  in  a  few  seconds  show  the 
presence  of  hydrochloric  acid.  The  acid  in  this  case  passes  through 
the  coats  of  the  intestine  against  the  pressure  of  the  current,  which  is 
of  course  directed  from  within  outward. 

Endosmosis  is  also  regulated,  in  great  measure,  by  temperature.  As 
a  rule  its  activity  is  increased  by  moderate  warmth.  Dutrochet  found 
that  an  endosmometer,  containing  a  solution  of  gum,  which  absorbed 
only  one  volume  of  water  at  a  temperature  of  0°,  absorbed  three 
volumes  at  about  34°  C.  Variations  of  temperature  will  sometimes 
even  change  the  direction  of  the  endosmotic  current,  particularly  with 
solutions  of  hydrochloric  acid.  In  the  experiments  of  Dutrochet,  when 
the  endosmometer  was  fiUed  with  dilute  hydrochloric  acid  and  placed 
in  distilled  water  at  the  temperature  of  10°  C.,  endosmosis  took  place 
from  the  acid  to  the  water,  if  the  density  of  the  acid  solution  were  less 
than  1.020 ;  but  from  the  water  to  the  acid,  if  its  density  were  greater 
than  this.  On  the  other  hand,  at  the  temperature  of  22°  C.,  the  current 
was  from  within  outward  when  the  density  of  the  solution  was  below 
1.003,  and  from  without  inward  when  it  was  above  that  point. 

Nature  of  Endosmosis  and  Exosmosis. 

The  continued  transudation  of  a  solution  through  an  animal  mem- 
brane and  its  diffusion  in  an  exterior  fluid  are  dependent  on  the  simul- 
taneous action  of  two  different  properties ;  first,  the  absorbent  capacity 
of  the  membrane  for  the  solution,  and  secondly,  the  capacity  of  the 


THE    LYMPHATIC    SYSTEM.  315 

solution  for  diffusing  itself  in  the  exterior  fluid.  The  simplest  illus- 
tration of  the  process  is  that  of  the  transudation  and  evaporation  of 
moisture.  If  a  fresh  animal  membrane  be  exposed  to  the  air  under 
ordinary  circumstances,  it  at  once  begins  to  lose  water  by  evaporation  ; 
and  the  loss  will  continue,  under  favorable  hygrometric  conditions, 
until  the  whole  of  the  water  has  disappeared  in  the  atmosphere  and 
the  membrane  is  completely  desiccated.  But  if  the  membrane  be 
placed  with  its  upper  surface  in  contact  with  the  air,  and  its  lower 
surface  in  contact  with  water  or  a  watery  fluid,  it  no  sooner  loses  a 
portion  of  its  water  by  evaporation  than  it  absorbs  a  corresponding 
quantity  from  beneath.  There  is  thus  a  continual  passage  of  water 
from  the  fluid,  through  the  membrane,  to  the  atmosphere,  until  the 
whole  of  it  has  been  exhausted ;  the  membrane  retaining  its  own 
proportion  of  moisture,  while  losing  water  by  one  surface  and  absorb- 
ing it  by  the  other. 

A  similar  interchange  will  take  place  if  one  surface  of  the  membrane 
is  in  contact  with  water  and  the  other  with  a  saline  or  saccharine  solu- 
tion ;  provided  the  solution  be  sufficiently  concentrated  to  absorb  water 
from  the  membrane.  Each  layer  of  the  membrane  absorbs  from  that 
next  to  it  sufficient,  moisture  to  replace  that  which  has  passed  into  the 
solution ;  and  endosmosis  thus  goes  on  from  the  water  to  the  solution 
through  the  animal  membrane. 

In  this  instance,  however,  there  will  be  a  double  action.  As  the 
membrane  has  an  absorptive  power  for  both  the  water  and  the  ingredi- 
ents of  the  solution,  and  as  these  two  are  diffusible  in  each  other,  they 
will  both  be  transferred  in  opposite  directions.  But  since  the  mem- 
brane absorbs  water  more  readily  than  the  ingredients  of  the  solution, 
it  can  supply  these  ingredients  to  the  water  on  one  side  less  abun- 
dantly than  it  can  supply  water  to  the  solution  on  the  other.  Con- 
sequently a  larger  volume  of  water  passes  to  the  solution  than  vice 
versa,  and  endosmosis  preponderates  over  exosmosis. 

It  is  evident  accordingly  that,  whatever  be  the  relation  of  the  two 
liquids  to  each  other,  the  first  requisite  for  their  transudation  is  the 
absorptive  power  of  the  animal  membrane.  A  membrane  in  contact 
with  two  different  liquids  will  nearly  always  absorb  one  of  them  more 
rapidly  than  the  other ;  and  if  in  contact  with  a  solution  containing 
several  ingredients,  it  will  take  up  some  of  these  ingredients  in 
greater,  others  in  smaller  proportion.  A  substance,  therefore,  which 
the  intervening  membrane  does  not  absorb  at  all,  cannot  be  transferred 
to  the  fluid  beyond  it.  The  membrane  acts  as  a  barrier  to  exclude 
ingredients  for  which  it  has  no  absorptive  power,  but  is  ready  to 
supply  those  which  it  can  take  up  with  facility. 

An  equally  important  condition  of  endosmosis  and  exosmosis  is  the 
diffusibility  of  different  liquids  in  each  other.  This  subject  was  inves- 
tigated by  Graham*  in  the  following  manner:  Glass  vessels,  filled 

*  Annalen  der  Chemie  und  Pharmacie.     Heidelberg,  1851.     Band  Ixxvii.,  p.  56. 


316  FUNCTIONS    OF    NUTRITION. 

with  various  saline  solutions,  were  immersed  in  reservoirs  of  pure 
water,  so  that  the  level  of  the  water  in  the  reservoir  was  a  little 
higher  than  that  of  the  solution  in  the  interior  vessel ;  and  after  they 
had  been  allowed  to  remain  for  a  time  at  rest,  at  a  constant  tempera- 
ture, the  quantity  of  solution  which  had  escaped  into  the  surrounding 
liquid  indicated  the  rapidity  with  which  diffusion  had  taken  place.  By 
this  method  it  was  found  that  the  diffusibility  of  different  liquids  varies 
in  an  analogous  way  with  their  absorption  by  animal  tissues,  and  is 
influenced  by  similar  conditions.  Solutions  of  diiferent  salts,  in  the 
same  degree  of  concentration,  are  diffused  with  different  degrees  of 
rapidity ;  and  the  same  solution,  other  conditions  remaining  equal, 
increases  in  dififusibility  with  the  elevation  of  temperature.  The  fol- 
lowing table  shows  the  comparative  diflfusibility  of  various  saline 
solutions  in  pure  water  at  different  temperatures : 

DIFFUSIBILITY  OF  SALINE  SOLUTIONS  IN  PURE  WATER. 

At  3°  C.  At  15.3°  C. 

Sodium  chloride      ....     22.47  .  .  .  32.25 

Sodium  nitrate         ....     22.79  .  .  .  30.70 

Ammonium  chloride       .         .         .31.14  .  .  .  40.20 

Potassium  nitrate   ....     28.70  .  .  .  35.55 

Potassium  iodide    ....     28.10  .  .  .  37.00 

Magnesium  sulphate        .        .        .     13.07  .  .  .  15.45 

The  rapidity  of  diffusion  is  influenced,  not  only  by  temperature,  but 
also  by  the  degree  of  concentration  of  the  solution  and  by  the  chemi- 
cal constitution  of  the  salt  which  it  contains.  A  concentrated  solution 
diffuses  into  pure  water  more  rapidly  than  one  which  is  comparatively 
dilute ;  and  if  the  solution  be  maintained  at  its  original  degree  of  con- 
centration while  the  exterior  liquid  is  replaced  by  pure  water,  diffusion 
continues  with  greater  energy  than  if  the  two  liquids  are  allowed  to 
become  changed  by  mutual  admixture.  Salts  of  potassium  diffuse 
more  rapidly  than  the  corresponding  salts  of  sodium ;  and  in  each 
instance  salts  of  the  monobasic  acids  diffuse  more  rapidly  than  those 
of  bibasic  acids  with  the  same  metals.  Sugar,  gum,  and  albumen 
are  less  diffusible  than  the  soluble  mineral  salts,  and  of  all  the 
substances  examined  albumen  is  the  least  so,  being  diffused  only 
one-twentieth  part  as  readily  as  sodium  chloride.  Urea,  on  the  other 
hand,  is  nearly  as  diffusible  as  sodium  chloride  If  the  interior  vessel 
contain  a  mixed  solution  of  several  substances,  each  is  diffused  with 
its  own  specific  rapidity,  so  that  after  a  time  they  are  found  in  the 
water  of  the  reservoir  in  different  quantities.  Various  other  peculiari- 
ties are  observed,  showing  the  influence  of  the  chemical  character  of  a 
salt  upon  its  diffusibility. 

In  the  experiments  of  Hoppe-Seyler,*  the  influence  of  repose  or  agi- 
tation on  the  rate  of  diffusion  was  fully  demonstrated.  Concentrated 
solutions  of  sugar,  albumen,  or  other  substances  having  a  rotatory 

*  Physiologische  Chemie.    Berlin,  1877,  p.  145. 


THE    LYMPHATIC    SYSTEM.  317 

action  on  polarized  light,  were  placed  at  the  bottom  of  a  glass  vessel, 
the  remainder  of  which  was  filled  with  pure  water.  The  quantity  of 
the  substance  in  solution  at  any  level  above  or  below  the  plane  of  con- 
tact of  the  two  liquids  could  then  be  determined  by  means  of  a  sac- 
charimeter  ;  and  the  examination  could  be  repeated  at  will  without  dis- 
turbing the  apparatus.  It  was  found  that,  under  these  conditions,  dif- 
fusion took  place  with  readiness  only  in  the  immediate  vicinity  of  the 
contact  of  the  two  liquids.  Solutions  of  gum  or  albumen  after 
several  days,  had  mingled  with  the  water  only  for  a  height  of  one 
or  two  centimetres  above  and  below  the  plane  of  contact ;  and  with  a 
concentrated  solution  of  cane  sugar,  at  the  end  of  four  weeks  the  layer 
of  diffusion  was  only  15  centimetres  in  thickness.  But  any  mechanical 
shock  or  disturbance  hastens  the  process  of  diffusion  and  admixture ; 
and  with  solutions  of  gum,  sugar,  or  albumen,  a  few  seconds'  agita- 
tion may  produce  a  uniform  mixture  which  would  require  an  indefinite 
time  by  diffusion  in  a  state  of  rest. 

Absorption  and  Translation  in  the  Living  Body. 

All  the  conditions  favorable  to  endosmosis  and  exosmosis,  shown 
by  the  above  experiments,  are  present  in  the  living  body.  The  organic 
tissues  and  membranes  have  their  normal  constitution  maintained  by 
the  process  of  nutrition,  and  exert  their  special  absorptive  power  on 
each  ingredient  of  the  animal  fluids.  The  extent  of  absorbing  surface 
is  multiplied  by  the  subdivision  of  the  blood-vessels,  the  glandular 
tubes,  and  the  anatomical  elements  of  the  organs.  The  fluids  are  in 
immediate  contact  with  the  absorbing  surfaces,  at  a  nearly  uniform, 
moderately  elevated  temperature ;  and  the  movement  of  the  blood  and 
lymph  supplies  the  requisite  ingredients  by  constant  renewal,  and  inces- 
santly removes  the  surplus  of  transuded  material. 

In  the  living  body,  accordingly,  transudation  takes  place  with  great 
rapidity.  It  has  been  shown  by  Gosselin,  that  if  a  watery  solution  of 
potassium  iodide  be  dropped  on  the  cornea  of  a  rabbit,  the  iodine 
passes  into  the  cornea,  aqueous  humor,  iris,  lens,  sclerotic  and  vitreous 
body,  in  the  course  of  eleven  minutes ;  and  that  it  will  penetrate  the 
aqueous  humor  in  three  minutes,  and  the  substance  of  the  cornea  in  a 
minute  and  a  half.  In  these  experiments  it  is  evident  that  the  iodine 
passes  into  the  deeper  portions  of  the  eye  by  endosmosis,  and  not  by 
transportation  through  the  blood-vessels ;  since  it  is  not  found  in  the 
tissues  of  the  opposite  eye,  examined  at  the  same  time. 

The  same  observer  has  shown  that  the  active  principle  of  belladonna 
penetrates  the  tissues  of  the  eyeball  in  a  similar  manner.  He  applied 
a  solution  of  atropine  sulphate  to  both  eyes  of  two  rabbits,  and  in 
half  an  hour  the  pupils  were  dilated.  Three-quarters  of  an  hour  later, 
the  aqueous  humor  was  collected  by  puncturing  the  cornea  with  a  trocar ; 
and  this  fluid,  dropped  on  the  eye  of  a  cat,  produced  dilatation  and 
immobility  of  the  pupil  in  half  an  hour.  The  aqueous  humor  of  the 
affected  eye  consequently  contains  atropine,  which  has  been  absorbed 


318  FUNCTIONS    OF    NUTRITION. 

through  the  cornea,  and  acts  directly  on  the  muscular  fibres  cf  the 
iris. 

But  in  all  vascular  organs,  endosmosis  and  exosmosis  are  further 
accelerated  by  the  movement  of  the  blood. 

If  a  solution  of  nux  vomica  be  injected  into  the  subcutaneous  con- 
nective tissue  of  the  hind  leg  of  two  rabbits,  in  one  of  which  the  local 
circulation  is  unimpeded,  while  in  the  other  it  has  been  arrested 
by  ligature  of  the  blood-vessels  of  the  limb,  in  the  first  animal  the 
poison  will  be  absorbed  with  sufficient  rapidity  to  produce  its  specific 
effects  in  a  few  minutes;  but  in  the  second,  absorption  will  be 
retarded,  and  the  poison  will  find  its  way  into  the  general  circulation 
so  slowly,  that  its  action  will  be  manifested  only  at  a  late  period,  or 
even  not  at  all. 

Albumen,  under  ordinary  conditions,  is  but  very  slightly  endosmotic 
or  diffusible ;  while  peptone  possesses  these  properties?  in  a  marked 
degree.  Peptone,  accordingly,  after  its  production  by  the  digestive  pro- 
cess, is  readily  absorbed  from  the  intestine  and  enters  the  blood-vessels ; 
but  the  albumen  of  the  blood,  in  the  normal  state  of  the  circulation,  is 
not  exuded  from  the  secreting  surfaces.  If  the  pressure,  however,  within 
the  capillary  vessels  be  increased  by  venous  obstruction,  not  only  the 
saline  and  watery  parts  of  the  blood  pass  out  in  larger  quantities, 
but  the  albumen  also  transudes  and  infiltrates  the  neighboring  parts. 
In  this  way  albumen  may  make  its  appearance  in  the  urine,  from  dis- 
turbance of  the  renal  circulation ;  and  local  cedema  or  general  ana- 
sarca  may  follow  upon  venous  congestion  in  particular  regions  or  at 
the  centre  of  the  circulation. 

The  Lymph  and  Chyle, 

The  lymph  is  the  fluid  which,  having  been  absorbed  from  the  various 
tissues  and  organs  of  the  body,  is  transported  by  the  lymphatic  vessels 
and  discharged  into  the  great  veins  near  the  heart.  As  the  chyle  is 
simply  the  fluid  of  the  mesenteric  lymphatics,  which  has  become  white 
and  opaque,  from  the  absorption  of  digested  fat,  it  is  properly  studied 
at  the  same  time  with  the  lymph  in  general.  Lymph  may  be  obtained 
from  the  living  animal  by  introducing  a  canula  into  the  thoracic  duct 
at  the  root  of  the  neck,  or  into  the  lymphatic  trunks  in  other  regions. 
It  was  collected  by  Rees  from  the  lacteals  of  the  mesentery  and  from 
the  lymphatics  of  the  leg  in  the  ass,  by  Colin  from  the  lacteals  and 
thoracic  duct  of  the  ox,  and  from  the  lymphatics  of  the  neck  in  the 
horse.  We  have  obtained  it  from  the  thoracic  duct  in  both  the  dog 
and  the  goat. 

Physical  Characters  and  Composition  of  Lymph. — The  lymph,  as 
obtained  from  the  thoracic  duct  in  the  intervals  of  digestion,  is  an 
opalescent  or  nearly  transparent,  alkaline  fluid,  usually  of  a  light  amber 
color,  and  having  a  specific  irrnvity  of  1022.  Its  analysis  shows  a  close 
resemblance  in  composition  with  the  plasma  of  the  blood.  It  contains 
water,  fibrinogen,  albumen,  fatty  matters,  and  the  usual  saline  sub- 


THE    LYMPHATIC    SYSTEM.  319 

stances  of  the  animal  fluids.  It  is,  however,  poorer  in  albuminous 
ingredients  than  the  blood.  The  following  is  an  analysis,  by  Lassaigne,* 
of  the  fluid  obtained  from  the  thoracic  duct  of  the  cow : 

COMPOSITION  OF  THE  LYMPH. 

Water                  964.0 

Fibrine       .  n  Q 

•          •          •          •  u.y 

Albumen    .......  28  0 

Fat .        '        *        1        !  0.4 

Sodium  chloride 50 

Sodium  carbonate  ") 

Sodium  phosphate  r  .....  12 

Sodium  sulphate     J 

Lime  phosphate 05 


1000.0 

Owing  to  the  presence  of  fibrinogen,  the  lymph  coagulates  like  blood, 
within  a  few  moments  after  its  removal  from  the  lymphatic  vessels, 
forming  a  gelatinous  mass,  more  or  less  colorless  and  transparent,  or 
whitish  and  opaque,  according  to  the  proportion  of  fatty  matter  present. 
After  coagulation,  it  separates  into  a  liquid  serum  and  a  solid  clot. 

In  lymph  from  the  thoracic  duct,  the  clot,  within  a  few  moments 
after  coagulation,  usually  assumes  a  pinkish  color,  and  on  microscopic 
examination  is  found  to  contain  a  few  red  blood-globules.  Their  pres- 
ence is  attributed  by  some  observers  (Kolliker,  Robin)  to  the  accidental 
rupture  of  capillary  blood-vessels  and  consequent  introduction  of  their 
contents  into  the  lymphatic  system  ;  but  their  occurrence  is  so  constant 
that  it  must  be  doubted  whether  they  are  altogether  of  accidental  origin. 
The  pinkish  color  is  never  perceptible  in  lymph  when  first  drawn  from 
the  vessels,  but  only  after.it  has  been  a  short  time  exposed  to  the  air. 

The  fluid  drawn  from  the  thoracic  duct,  especially  in  carnivorous 
animals,  varies,  both  in  appearance  and  constitution,  at  diiferent  times. 
In  the  ruminating  and  graminivorous  animals,  as  the  sheep,  ox,  goat, 
and  horse,  it  is  either  opalescent,  with  a  slight  amber  tinge,  or  nearly 
transparent  and  colorless.  In  the  dog  and  cat,  it  is  also  opaline  and 
amber  colored  in  the  intervals  of  digestion,  but  soon  after  feeding 
becomes  of  a  dense,  milky  white,  and  continues  to  present  that  appear- 
ance until  digestion  and  absorption  are  complete.  It  then  regains  its 
original  aspect,  and  remains  opaline  until  digestion  is  again  in  progress. 

This  variation  is  due  to  the  absorption  of  fatty  matters  during 
digestion.  The  chyle  is  richer  than  lymph  in  nearly  all  its  solid  in- 
gredients, but  the  principal  difference  between  the  two  consists  in  the 
proportion  of  fat,  which  is  nearly  absent  from  the  transparent  or 
opaline  lymph,  but  abundant  in  the  white  and  opaque  chyle.  This 
is  shown  in  the  following  analysis,  by  Rees,f  of  lymph  and  chyle, 

*  In  Colin,  Physiologie  compare  des  Animaux  domestiques.  Paris,  1856,  tome 
ii.,  p.  111.  ^ 

•*•  London  Medical  Gazette.     London,  1841,  vol.  i.,  p.  547. 


320  FUNCTIONS    OF    NUTRITION. 

taken  respectively  from  the  lacteals  of  the  abdomen  and  the  lymphatics 
of  the  hind  leg,  in  the  ass. 

COMPARATIVE  ANALYSIS  OF  LYMPH  AND  CHYLE. 

Lymph.  Chyle. 

Water 965.36  902.37 

Albumen 12.00  35.16 

Fibrine 1.20  3.70 

Spirit  extract 2.40  3.32 

Water  extract 13.19  12.33 

Fat traces  36.01 

Saline  matter  5.85  7.11 


1000.00          1000.00 

When  a  canula,  accordingly,  is  introduced  into  the  thoracic  duct  at 
different  periods  after  feeding,  the  fluid  discharged  varies  considerably, 
both  in  appearance  and  quantity.  In  the  dog,  it  is  never  quite  trans- 
parent, but  retains  a  marked  opaline  tinge  even  so  late  as  eighteen 
hours  after  feeding  on  lean  meat,  and  at  least  three  days  and  a  half 
after  the  introduction  of  fat  food.  Soon  after  feeding,  it  becomes 
whitish  and  opaque,  and  so  remains  during  the  continuance  of  diges- 
tion and  absorption.  After  this  it  resumes  its  former  appearance, 
becoming  light  colored  and  opalescent  in  the  carnivorous  animals,  and 
nearly  transparent  in  the  herbivora. 

The  Lymph  Globules. — The  lymph  nearly  always  contains  rounded, 
transparent,  or  finely  granular  nucleated  cells,  from  6  to  12  mmm.  in 
diameter,  similar  in  appearance  to  the  white  globules  of  the  blood, 
and  known  as  "lymph-globules."  According  to  Kolliker  they  vary 
much,  both  in  number  and  size,  according  to 'the  part  of  the  lymphatic 
system  from  which  the  fluid  is  taken.  In  the  smallest  lymphatic  ves- 
sels of  the  mesentery,  they  are  scanty  or  altogether  absent ;  and  in 
the  lymphatics,  where  they  first  show  themselves,  they  are  few  in 
number  and  of  small  size.  But  after  the  lymph  has  traversed  one  or 
two  ranges  of  lymphatic  glands,  the  globules  are  more  numerous  and 
larger,  often  attaining  the  size  of  12  mmm.  in  diameter.  From  this 
circumstance,  as  well  as  from  the  microscopic  texture  of  the  lymph- 
atic glands,  it  is  concluded  that  the  lymph-globules  originate,  in  great 
part,  in  the  interior  of  the  glands,  and  that  they  are  brought  thence 
by  the  current  traversing  the  lymph-paths  in  the  substance  of  these 
organs. 

Movement  of  the  Lymph  in  the  Lymphatic  Vessels. — The  move- 
ment of  the  fluid  in  the  lymphatic  system  differs  from  that  of  the 
blood,  in  the  important  particular  that  its  course  is  always  in  one 
direction,  namely,  from  the  periphery  toward  the  centre.  It  is  ab- 
sorbed by  the  lymphatic  capillaries,  collected  into  the  lymphatic 
branches  and  trunks,  and  thence  conducted  to  the  great  veins  near 
the  right  side  of  the  heart. 


THE    LYMPHATIC    SYSTEM.  321 

The  cause  of  this  centripetal  movement  of  the  lymph  is  primarily 
the  force,  of  endosmosis  acting  at  the  confines  of  the  lymphatic  svstem. 
As  the  volume  of  fluid  accumulates  in  an  endosmometer,  the  ingre- 
dients of  the  lymph  penetrate  by  absorption  into  the  lymphatic 
capillaries,  and  thence  into  the  larger  vessels  of  the  system.  It  is 
evident  that  the  pressure  of  a  fluid  from  endosmotic  action  may  be 
very  considerable,  since  it  can  sustain  a  column  of  mercury  at  the 
height  of  600  millimetres,  and  may  burst  the  shell  membrane  of  a 
fowl's  egg  placed  in  contact  with  water.  As  this  pressure,  in  the 
lymphatic  system,  is  always  from  without  inward,  and  as  the  main 
lymphatic  trunks  terminate  in  the  veins,  the  result  is  a  uniform  move- 
ment of  the  lymph,  from  the  peripheral  parts  toward  the  centre  of  the 
circulation. 

As  the  lymphatic  vessels,  like  the  veins,  are  provided  with  valves, 
opening  toward  the  centre  and  closing  toward  the  periphery,  the  con- 
traction and  relaxation  of  the  voluntary  muscles  in  the  limbs  and 
trunk  must  facilitate  the  passage  of  the  fluids  in  an  inward  direction. 
The  pulsations  of  the  heart  and  aorta  also  contribute  to  this  result. 
As  the  thoracic  duct  passes  obliquely  through  the  chest,  between  the 
spinal  column  and  the  aorta,  at  each  aortic  pulsation  it  is  compressed, 
and  its  contents  propelled  upward.  This  effect  is  often  visible  in  the 
experiment  of  collecting  lymph  from  the  thoracic  duct  at  the  root  of 
the  neck ;  the  lymph  being  often  projected  from  the  extremity  of  the 
canula  in  a  distinct  jet  at  each  cardiac  pulsation. 

Lastly,  the  respiratory  movements  of  the  chest  take  part  in  main- 
taining the  flow  of  lymph.  At  each  inspiration  the  resistance  in  the 
thorax  is  diminished,  and  the  lymph  passes  more  readily  from  below 
into  the  thoracic  duct ;  at  each  expiration  the  duct  is  subjected  to  com- 
pression and  thus  emptied  toward  the  veins.  When  artificial  respira- 
tion is  kept  up  through  the  trachea  after  the  chest  has  been  opened, 
the  influence  of  the  respiratory  movement  is  reversed.  The  flow  of 
lymph  from  the  thoracic  duct  is  then  perceptibly  increased  at  each 
insufflation  of  the  lung,  since  this  produces  a  momentary  pressure 
within  the  chest. 

Of  the  forces  above  enumerated  for  the  production  of  the  lymph- 
current,  the  most  important  and  continuous  is  endosmotic  action.  The 
remainder  are  more  or  less  irregular  or  intermittent,  but  they  con- 
tribute by  mechanical  aids  to  the  same  result ;  and  the  effect  of  the 
whole  is  an  incessant  transportation  of  the  lymph  from  the  periphery 
to  the  centre,  where  it  is  mingled  with  the  returning  current  of  venous 
blood. 

Daily  Quantity  of  the  Lymph  and  Chyle.— The  quantity  of  fluid 
passing  through  the  thoracic  duct  varies  according  to  the  condition  of 
abstinence  or  digestion.  In  the  fasting  condition  it  is  comparatively 
moderate,  but  becomes  more  abundant  soon  after  the  commencement 
of  digestion,  to  diminish  again  during  its  later  stages.  We  have  found, 
at  various  periods  after  feeding,  in  the  dog,  the  following  quantities 

V 


322  FUNCTIONS    OF    NUTRITION. 

discharged  from  the  thoracic  duct  per  hour,  for  every  thousand  parts 
of  bodily  weight : 

HOUELY  QUANTITIES  OF  LYMPH  AND  CHYLE  IN  THE  DOG, 
PER  THOUSAND  PARTS  OF  BODILY  WEIGHT. 

3J  hours  after  feeding 2.45 

7        "        "          "              2.20 

13                             "               0.99 

18        "         "          "               1.15 

18J      "                                    1.99 

It  would  thus  appear  that  the  hourly  quantity  of  these  fluids,  after 
increasing  with  digestion  and  diminishing  during  its  latter  stages, 
again  increases  somewhat  about  the  eighteenth  hour.  It  is  probable 
that  this  double  increase  is  owing  to  two  causes.  The  fluid  obtained 
in  greatest  abundance  in  the  dog,  from  3  to  7  hours  after  feeding, 
is  white  and  very  opaque,  and  its  quantity  is  largely  due  to  the 
admixture  of  chyle  absorbed  from  the  intestine.  That  drawn  about 
the  eighteenth  hour  is  opaline,  or  nearly  transparent,  and  consists  of 
lymph  alone.  The  absorption  of  chyle,  therefore,  takes  place  while 
digestion  is  in  progress ;  but  the  production  of  lymph  occurs  most 
abundantly  some  hours  later,  after  the  materials  of  nutrition  have 
reached  and  permeated  the  tissues. 

The  daily  quantity  of  lymph  and  chyle  has  been  found,  by  direct 
observation,  much  larger  than  would  be  anticipated.  In  two  experi- 
ments on  the  horse,  extending  over  a  period  of  twelve  hours  each, 
Colin  *  obtained  from  the  thoracic  duct,  on  the  average,  893  grammes 
of  fluid  per  hour,  which,  if  continued  for  the  remaining  twelve  hours, 
would  amount  to  rather  more  than  20  kilogrammes  per  day.  In  the 
ruminating  animals,  according  to  the  same  observer,  the  quantity  is 
still  greater.  In  a  cow  of  ordinary  size,  the  smallest  amount  obtained, 
in  an  experiment  extending  over  twelve  hours,  was  625  grammes  in 
fifteen  minutes ;  that  is,  2500  grammes  per  hour,  or  60  kilogrammes 
per  day.  In  another  experiment  with  a  young  bull  weighing  185 
kilogrammes,  he  withdrew  from  the  thoracic  duct  in  twenty-four  hours, 
15  kilogrammes  of  lymph  and  chyle,  representing  a  little  more  than 
8  per  cent,  of  the  entire  bodily  weight. 

We  have  obtained  similar  results  in  the  dog  and  the  goat.  In  a 
young  kid  weighing  6.36  kilogrammes,  122.5  grammes  of  lymph  were 
collected  from  the  thoracic  duct  in  three  hours  and  a  half.  This  rep- 
resents 35  grammes  per  hour,  and,  if  continued  throughout  the  day, 
would  amount  to  640  grammes,  or  fully  10  per  cent,  of  the  bodily 
weight.  In  the  dog  the  fluids  from  the  thoracic  duct  were  less  abun- 
dant; the  total  daily  quantity  in  this  animal,  according  to  the  aver:iir«' 
of  observations  at  various  periods  after  feeding,  being  very  nearly 
four  and  a  half  per  cent,  of  the  bodily  weight.  This  is  substan- 

*  Physiologic  compare'e  des  Animaux  domestiques.     Paris,  1856,  tome  ii.,  p.  106. 


THE    LYMPHATIC    SYSTEM.  323 

tially  the  same  result  as  that  obtained  by  Colin  in  the  horse ;  and 
for  a  man  weighing  65  kilogrammes,  it  would  be  equivalent  to  about 
3000  grammes  of  lymph  and  chyle  per  day.  This  represents  both  the 
products  of  lymphatic  transudation  and  those  of  intestinal  absorption. 
An  estimate  of  the  lymph  alone  must  be  based  upon  the  quantity  of 
fluids  passing  through  the  thoracic  duct  in  the  intervals  of  digestion, 
when  no  chyle  is  absorbed  from  the  intestine.  In  the  dog,  the  aver- 
age quantity  obtained,  from  the  thirteenth  to  the  nineteenth  hour 
after  feeding,  was  about  1.30  per  thousand  parts  of  the  bodily  weight ; 
or,  for  the  whole  twenty-four  hours,  a  little  over  3  per  cent,  of  the 
bodily  weight.  For  a  man  of  medium  size,  this  would  give  not  far 
from  2000  grammes  as  the  average  daily  quantity  of  lymph  alone. 

Internal  Renovation  of  the  Animal  Fluids. — The  combined  opera- 
tion of  secretion,  transudation,  and  reabsorption  produces  a  continual 
interchange  of  the  animal  fluids,  which  is  dependent  for  its  materials 
upon  the  blood,  and  which  may  be  considered  as  a  kind  of  secondary 
circulation  through  the  substance  of  the  tissues.  All  the  fluids  dis- 
charged into  the  small  intestine  are  reabsorbed  and  again  enter  the 
current  of  the  circulation.  They  pass  and  repass  through  the  mucous 
membrane  of  the  alimentary  canal  and  adjacent  glands,  becoming  more 
or  less  altered,  but  still  serving  to  renovate  alternately  the  blood  and 
the  secretions.  The  elements  of  the  blood  transude  in  part  from  the 
capillary  vessels,  and  are  taken  up  from  the  tissues  by  the  lymphatics, 
to  be  again  restored  to  the  circulation  at  its  venous  extremity. 

The  quantity  of  fluids  thus  transuded  and  reabsorbed  will  serve  to 
indicate  the  activity  of  endosmosis  and  exosmosis  in  the  living  body. 
In  the  following  table,  the  amounts  are  estimated,  from  the  preceding 
data,  for  a  man  of  average  size : 

FLUIDS  TRANSUDED  AND  REABSORBED  DURING  TWENTY-FOUR  HOURS. 

Saliva 1280  grammes. 

Gastric  juice 3000 

Pancreatic  juice 800        " 

Bile 1000        " 

Lymph 2000         lt 

8080         " 

Not  less  than  8000  grammes  therefore  of  the  animal  fluids,  a  quantity 
equal  to  that  of  the  entire  blood  and  amounting  to  more  than  12  per 
cent,  of  the  bodily  weight,  transude  through  the  membranes  and  are 
restored  to  the  blood  by  reabsorption,  in  the  course  of  a  day.  By  this 
process  the  natural  constitution  of  the  parts,  though  constantly  changing, 
is  maintained  in  its  normal  condition,  through  the  movement  and  reno- 
vation of  the  circulating  fluids. 


CHAPTER  VIII. 
THE    HEINE. 

urine  is  distinguished  from  other  animal  fluids  by  the  fact 
J-  that  it  represents  the  product  of  physiological  disintegration.  The 
various  manifestations  of  force  in  the  living  body,  such  as  heat,  sen- 
sibility, and  motion,  are  produced  at  the  expense  of  its  materials,  by 
their  metamorphosis  in  the  process  of  nutrition.  The  transformation 
and  renewal  of  its  constituents  are  accordingly  essential  conditions  of 
its  vital  activity.  Every  living  being  absorbs  from  without  nutritive 
materials,  which  are  modified  by  assimilation  and  converted  into  the 
ingredients  of  its  tissues ;  and  at  the  same  time  its  elements  pass  into 
new  forms  of  combination,  to  be  expelled  as  the  products  of  disinte- 
gration. 

Certain  substances,  therefore,  are  constantly  making  their  appearance 
in  the  body,  which  were  not  introduced  with  the  food,  but  which  have 
been  produced  by  retrograde  metamorphosis.  They  are  derived  from 
materials  which  once  formed  part  of  the  animal  tissues,  but  which  have 
become  altered  by  internal  transformation,  and  are  no  longer  capable  of 
aiding  in  the  performance  of  the  functions.  The  elimination  and  re- 
moval of  these  materials  is  the  process  of  excretion,  and  the  materials 
themselves  are  known  as  excrementitious  substances. 

The  excrerilentitious  substances  are  formed  for  the  most  part  in  the 
tissues,  from  which  they  are  absorbed  by  the  blood  and  conveyed  to 
excretory  organs  by  which  they  are  discharged.  If  their  elimination 
be  impeded,  their  accumulation  in  the  system  produces  a  disturbance, 
which  is  more  or  less  severe  according  to  their  special  character  and 
the  rapidity  of  their  production.  This  disturbing  influence  is  especially 
manifested  in  its  action  upon  the  nervous  system,  causing  abnormal 
irritability,  derangement  of  the  senses,  and,  in  extreme  cases,  delirium, 
insensibility,  and  death. 

In  the  normal  condition  and  in  normal  quantities,  the  exoremcnti- 
tious  matters  are  not  poisonous,  nor  even  deleterious;  they  are  the 
natural  products  of  functional  activity,  and  therefore  as  essential  to 
the  manifestation  of  life  as  the  nutritious  material  supplied  by  the 
food.  It  is  only  when  their  elimination  is  retarded  that  they  interfere 
with  the  performance  of  the  functions,  by  deranging  the  constitution 
of  the  tissues. 

Some  of  the  excrementitious  matters  produced  in  the  body  are  prob- 
ably eliminated,  in  small  proportion,  with  the  perspiration  or  the  frees; 
and  carbonic  acid  is  abundantly  exhaled  from  the  lungs.  But  among 

324 


THE    URINE.  325 

the  most  important  of  these  substances  are  those  which  contain  nitrogen. 
This  element  indicates  their  derivation  from  the  albumenoid  ingredients 
of  the  body,  and  they  present  in  other  respects  a  mutual  analogy  in 
chemical  properties  and  composition.  They  accordingly  form  a  group 
of  organic  substances,  resembling  each  other  in  origin,  constitution, 
and  physiological  destination.  They  are  eliminated  from  the  body  by 
the  urine,  of  which  they  form  the  characteristic  ingredients. 

The  urine  is  therefore  solely  an  excretion.  It  is  a  solution  of  the 
nitrogenous  excrementitious  matters  of  the  body ;  and  by  its  abundance 
and  composition  it  indicates  the  activity  of  metamorphosis  in  the  nitro- 
genous ingredients  of  the  tissues  and  fluids.  It  also  contains  most  of 
the  mineral  salts  discharged  from  the  body ;  and  by  the  water  which 
holds  these  matters  in  solution  it  represents  a  large  proportion  of  the 
fluids  passing  through  the  system.  Furthermore,  accidental  or  abnor- 
mal ingredients,  introduced  into  the  blood,  are  usually  eliminated  by 
this  channel,  and  appear  as  temporary  ingredients  of  the  urine.  The 
constitution  and  variations  of  the  urine  during  health,  and  its  altera- 
tion in  disease,  are  regulated  by  the  corresponding  changes  of  nutrition 
in  the  body  at  large.  It  is  therefore  one  of  the  most  essential  products 
of  the  animal  system,  and  its  formation  is  second  in  importance  only  to 
the  function  of  respiration. 

Physical  Properties  of  the  Urine. 

The  urine  is  a  clear,  amber-colored  fluid,  of  a  watery  consistency 
and  distinctly  acid  reaction.  It  is  usually  so  nearly  transparent,  that 
no  turbidity  is  perceptible  by  ordinary  diffused  light.  It  contains, 
however,  a  small  quantity  of  mucus  from  the  urinary  bladder,  which 
becomes  visible  as  a  faint  opalescence  when  a  sunbeam  is,  made  to  pass 
through  it  in  a  lateral  direction.  After  remaining  for  some  hours  at 
rest  in  a  cylindrical  vessel,  the  mucus  subsides,  forming  a  light  cloud 
at  the  bottom  and  leaving  the  supernatant  fluid  clear.  The  average 
specific  gravity  of  healthy  urine,  in  the  adult,  is  from  1020  to  1025 ; 
and  its  daily  quantity  about  1200  cubic  centimetres. 

Variations  in  Quantity,  Acidity,  and  Specific  Gravity. — The  urine 
is  habitually  discharged  from  the  bladder  five  or  six  times  in  the  twenty- 
four  hours,  each  specimen  showing  more  or  less  variation  in  its  physical 
properties.  This  depends  on  the  changing  conditions  of  the  body,  as 
to  rest,  exercise,  food,  drink,  sleep,  and  wakefulness.  In  the  same 
person,  leading  a  uniform  mode  of  life,  the  diurnal  variations  of  the 
urine  follow  each  other  with  considerable  regularity ;  though  they  may 
not  be  altogether  the  same  in  different  individuals.  As  a  rule,  the 
urine  which  collects  during  the  night  and  is  first  discharged  in  the 
morning  is  strongly  colored,  of  high  specific  gravity,  with  a  very  dis- 
tinct acid  reaction.  During  the  forenoon  it  is  pale  and  of  diminished 
density  ;  its  specific  gravity  often  falling  so  low  as  1018  or  1015.  At 
the  same  time,  its  acidity  diminishes  or  disappears ;  so  that  it  may  be 
either  faintly  acid,  neutral,  or  slightly  alkaline.  Its  density  and  depth 


326  FUNCTIONS    OF    NUTRITION. 

of  color  then  increase,  and  its  acidity  returns ;  all  these  properties 
becoming  more  strongly  marked  during  the  afternoon  and  evening. 
Toward  night  it  is  again  deeply  colored  and  strongly  acid,  and  its 
specific  gravity  often  1028  or  1030. 

These  variations  are  liable  to  modification  from  temporary  causes. 
The  color,  acidity,  and  specific  gravity  of  the  urine  may  be  diminished 
at  any  time  by  large  draughts  of  liquid  or  the  use  of  diuretic  mineral 
waters;  or  they  may  be  increased  by  abstinence  from  drink  or  by 
copious  perspiration.  Its  acidity  is  also  liable  to  vary  from  the  use 
of  food,  such  as  summer  fruits  or  vegetables,  containing  salts  of  the 
organic  acids,  namely,  lactates,  acetates,  malates,  and  tartrates.  These 
salts,  when  introduced  into  the  system,  are  replaced  by  carbonates  of 
the  same  bases  and  appear  under  that  form  in  the  urine,  reducing  for 
the  time  its  acidity,  or  even  causing  its  alkalescence. 

It  is  evident,  therefore,  that  when  the  specific  gravity  and  acidity 
of  the  urine  are  to  be  tested,  it  will  not  be  sufficient  to  rely  upon  the 
examination  of  a  single  specimen.  Its  normal  variation  in  specific 
gravity  may  reach  the  limits  of  1015  as  a  minimum  and  1030  as  a 
maximum ;  but  either  of  these  would  be  unnatural  if  continued  for 
twenty-four  hours.  All  the  specimens  of  urine  passed  during  the  day 
should  therefore  be  collected  and  examined  together.  The  mean  specific 
gravity  thus  obtained  will  represent  its  normal  daily  density. 

Its  daily  volume  is  also  to  be  taken  into  account.  The  total  amount 
of  solids  discharged  by  the  urine  in  health  is  from  50  to  GO  grammes 
per  day;  and  this  quantity  is  dissolved  in  about  1200  cubic  centimetres 
of  water.  This  gives  an  average  daily  quantity  and  an  average  specific 
gravity  of  the  urine,  as  the  measure  of  the  excretory  process  during 
twenty-four  hours. 

Both  the  quantity  of  the  urine  and  its  mean  specific  gravity  are 
liable  to  vary  in  the  same  individual  from  day  to  day ;  but  when  this 
is  due  to  physiological  or  temporary  causes,  the  variations  of  quantity 
and  specific  gravity  are  in  inverse  ratio  to  each  other.  Usually  the 
water  of  the  urine  is  more  than  sufficient  to  hold  all  its  solid  matters 
in  solution;  and  its  proportion  may  therefore  be  lessened  without 
the  production  of  turbidity  or  the  formation  of  a  deposit,  the  urine 
merely  becoming  deeper  in  color,  and  of  higher  specific  gravity.  If 
the  quantity  of  drink  be  diminished,  or  if  the  exhalation  from  the 
lungs  and  skin,  or  the  intestinal  discharges,  be  increased,  a  smaller 
quantity  of  water  will  pass  off  by  the  kidneys ;  and  the  urine  will  be 
diminished  in  quantity,  while  its  specific  gravity  is  increased.  The 
urine  is  sometimes  reduced  in  this  way  to  500  or  600  cubic  centi- 
metres per  day,  its  mean  specific  gravity  rising  at  the  same  time  to 
1030.  On  the  other  hand,  if  the  fluid  ingesta  be  unusually  abundant, 
or  if  the  perspiration  be  diminished,  the  surplus  water  will  pass  off  by 
the  kidneys;  the  amount  of  urine  in  twenty-four  hours  being  increased 
to  1500  or  1GOO  cubic  centimetres,  and  its  mean  specific  gravity  reduced 
to  1020  or  1015.  These  changes  depend  simply  on  the  fluctuating 


THE    URINE. 


327 


quantity  of  water  in  the  urine ;  its  total  amount  of  solid  matter  re- 
maining about  the  same.  If,  however,  both  its  quantity  and  mean 
specific  gravity  be  increased  or  diminished  at  the  same  time,  or  if  either 
one  be  increased  or  diminished  while  the  other  remains '  stationary, 
this  would  show  an  actual  change  in  the  amount  of  solid  ingredients^ 
and  consequently  an  abnormal  condition. 

Ingredients  of  the  Urine. 

The  chemical  composition  of  the  urine,  as  derived  from  numerous 
analyses,  is  as  follows : 


COMPOSITION  OF  THE  URINE. 


Nitrogenous 

organic 
substances. 


Mineral  salts. 


Water 

Urea 

Creatinine      .... 
Sodium  and  potassium  nrates 
[  Sodium  and  potassium  hippurates  , 
Sodium  bi phosphate 
Sodium  and  potassium  phosphates 
Lime  and  magnesium  phosphates 
Sodium  and  potassium  chlorides     , 
Sodium  and  potassium  sulphates 
Mucus  and  coloring  matter 


950.00 
26.20 
0.87 
1.45 
0.70 
0.40 
3.35 
0.83 
12.55 
3.30 
0.35 

1000.00 


Urea. — This  is  the  most  important  constituent  of  the  urine,  both  in 
character  and  amount,  forming  more  than  one-half  its  solid  ingredients, 
and  over  80  per  cent,  of  all  those  of  an  organic  nature.  The  most 
important  fact  known  with  regard  to  the  origin  of  urea  is,  that  it  is 
not  formed  in  the  kidneys,  but  pre-exists  in  the  blood  and  is  drained 
away  from  the  circulating  fluid  during  its  passage  through  the  renal 
vessels.  It  has  been  found  in  the  blood  of  the  human  subject  in  cases 
of  renal  disease,  in  so  large  a  proportion  as  1.5  parts  per  thousand,* 
or  nearly  ten  times  its  normal  quantity. 

Urea  is  most  readily  obtained  from  urine  by  first  converting  it  into 
a  nitrate.  For  this  purpose  the  fresh  urine  is  evaporated  over  the 
water-bath  to  one-quarter  of  its  original  volume.  It  is  then  filtered, 
and  the  filtered  fluid  mixed  with  an  equal  quantity  of  nitric  acid.  The 
nitrate  of  urea  thus  produced,  being  less  soluble  than  urea,  is  deposited 
in  abundant  crystalline  scales.  The  deposit  is  separated  by  filtration 
from  the  mother  liquor,  mixed  with  water,  and  decomposed  by  the 
addition  of  barium  carbonate,  which  sets  free  the  urea,  with  the  forma- 
tion of  barium  nitrate.  This  process  is  continued  so  long  as  carbonic 
acid  is  given  off;  after  which  the  whole  is  evaporated  to  dryness,  and 
the  dry  residue  extracted  with  absolute  alcohol,  which  dissolves  the 


*  In  Milne  Edwards,  Le9ons  sur  la  Physiologic.     Paris,  1857,  tome  i.,  p.  298. 


328  FUNCTIONS    OF    NUTRITION. 

urea.  The  alcoholic  solution  is  then  filtered  and  evaporated  until  the 
urea  separates  in  a  crystalline  form.* 

The  quantity  of  urea  in  a  given  volume  of  urine  is  ascertained  by 
decomposing  it,  according  to  Davy's  method,  with  a  solution  of  sodium 
hypochlorite.  A  narrow  graduated  glass  tube,  open  at  one  extremity, 
with  a  capacity  of  about  50  cubic  centimetres,  is  filled  to  a  little  more 
than  one-third  its  height  with  mercury,  upon  which  are  poured  3  or  4 
cubic  centimetres  of  the  urine  to  be  examined.  The  remainder  of  the 
tube  is  then  filled  with  the  sodium  hypochlorite  solution,  its  mouth 
closed,  the  fluids  well  mixed  by  agitation,  and  the  tube  inverted  in 
a  shallow  dish  filled  with  a  saturated  solution  of  sodium  chloride. 
The  mixture  of  urine  and  hypochlorite  solution  remains  in  the  tube ; 
and  as  the  urea  is  decomposed,  its  nitrogen  collects  in  the  upper  end  of 
the  tube,  where  its  volume  may  be  read  off  on  the  scale,  after  the  action 
has  ceased.  Every  cubic  centimetre  of  nitrogen,  thus  disengaged,  rep- 
resents 2.5  milligrammes  of  urea. 

The  results  obtained  by  nearly  all  experimenters  led  to  the  conclu- 
sion that  the  quantity  of  urea  excreted  is  especially  increased  by  mus- 
cular exertion,  until  a  doubt  was  thrown  on  this  point  by  Fick  and 
Wislicenus  in  1866.  These  observers  ascended  a  mountain  on  foot,  the 
ascent  occupying  a  little  over  eight  hours ;  during  which  time,  and  for 
seventeen  hours  beforehand,  they  confined  themselves  to  a  diet  of  non- 
nitrogenous  food.  They  found  the  hourly  amount  of  urea  discharged 
less  during  the  ascent  than  it  was  before ;  but  it  increased  during  the 
following  night,  after  a  meal  of  animal  food. 

Subsequent  observers  have  obtained  various  results.  Parkes,*)*  in  a 
series  of  extended  observations,  found  that  the  discharge  of  urea  was 
increased  not  during,  but  after,  a  period  of  muscular  work.  This  was 
shown  even  in  a  man  confined  for  five  days  to  a  non-nitrogenous  diet, 
in  whom  the  discharge  of  urea  was  not  increased  on  the  day  of  unusual 
muscular  effort,  but  on  the  following  day  was  a  little  more  than  doubled. 

The  observations  of  Flint,  J  in  the  case  of  the  pedestrian  Weston, 
have  the  advantage  of  extending  over  comparatively  long  periods,  both 
of  exercise  and  rest,  the  diet  remaining  unchanged  in  general  character. 

The  pedestrian  was  under  observation  for  fifteen  days ;  namely,  five 
days  previous  to  the  walk,  five  days  during  its  continuance,  and  five 
days  immediately  afterward.  For  the  period  preceding  the  walk,  the 
average  exercise  was  about  eight  miles  per  day ;  during  the  walk  it 
was  nearly  sixty-four  miles  per  day,  and  for  the  subsequent  period  a 
little  over  two  miles  per  day.  The  results  obtained  represent  accord- 
ingly the  amount  of  urea  excreted  under  ordinary  conditions,  that  dis- 
charged during  unusual  muscular  exertion,  and  the  subsequent  effects 
of  the  exertion  on  the  general  system. 

*  Hoppe-Seyler,  IIandl>ueh  der  Physiologisch-  und  Pathologisch-Chemischen 
Analyse.  Berlin,  1870,  p.  120. 

f  Proceedings  of  the  Koval  Society  of  London,  vol.  xvi.,  p.  48,  and  March  2, 1871. 
t  New  York  Medical  -Journal,  June,  1871. 


THE    URINE. 


329 


The  nitrogenous  ingredients  of  the  food,  during  all  three  periods, 
were  also  recorded,  so  that  their  influence  could  be  estimated  at  the 
same  time  with  that  of  the  muscular  exertion. 

The  following  table  gives  the  main  result  of  these  experiments,  as 
connected  with  the  present  subject : 


Daily  Quantity  of 

First  Period. 
Five  days 
before  the  walk. 

Second  Period. 
Five  days 
during  the  walk. 

Urea       

Nitrogen  in  food     . 
Nitrogen  in  urea     . 
Total  nitrogen  in  urea  and  feces 
Nitrogen  in  urea  and  feces  per 
100  parts  of  nitrogen  in  food 

628.24  grains. 
339.46       " 
293.18       u 
315.09      " 

92.82 

722.16  grains. 
234.76       " 
337.01       " 
361.52       " 

153.99 

Third  Period. 

Five  days 
after  the  walk. 

726.79  grains. 
440.93      " 
339.17      " 
373.15      " 

84.63 


It  is  evident,  therefore,  that  during  unusual  muscular  exertion  the 
daily  quantity  of  urea  was  increased  by  nearly  fifteen  per  cent,  the 
nitrogenous  elements  of  the  food  being  at  the  same  time  diminished ; 
and  that  the  total  quantity  of  nitrogen  discharged  by  the  urea  and  feces 
combined  was  more  than  fifty  per  cent,  greater  than  that  introduced 
with  the  food,  while  in  both  the  previous  and  subsequent  periods  it 
was  from  seven  to  fifteen  per  cent.  less.  Five  years  later,  observations 
were  made  on  the  same  pedestrian  by  Pavy,*  during  a  six  days'  walk, 
averaging  75  miles  per  day,  with  similar  results ;  there  being  an 
increased  discharge  of  urea,  and  an  increased  elimination  of  nitrogen 
not  accounted  for  by  that  taken  with  the  food. 

Creatinine. — This  substance  is  closely  allied  to  urea  in  chemical  com- 
position, but  is  .produced  in  much  smaller  quantity ;  its  total  amount 
not  usually  exceeding  1  gramme  per  day.  It  is  probably,  like  urea,  a 
final  product  of  the  metamorphosis  of  albumenoid  matters,  but  it  is  no 
doubt  immediately  derived  from  the  creatine  of  muscular  tissue,  from 
which  it  may  be  artificially  produced  by  the  action  of  heat  and  dilute 
sulphuric  acid.  But  little  is  known  with  regard  to  the  conditions 
which  increase  or  diminish  its  production  in  the  body. 

Sodium  and  Potassium  Urates. — The  uric  acid  of  the  sodium  and 
potassium  urates  is  a  nitrogenous  organic  acid,  belonging  to  the  class 
of  excrementitious  matters.  Like  urea,  it  is  increased  in  quantity  by  a 
nitrogenous,  and  decreased  by  a  non-nitrogenous  diet ;  but  its  relations 
to  muscular  exercise  and  other  temporary  conditions  are  not  fully 
known.  The  urates  are  readily  soluble  in  water,  and  are  usually  ex- 
creted to  the  amount  of  about  1.75  gramme  per  day.  The  hippurates 
are  similar  in  their  general  physiological  relations  to  the  urates,  except- 
ing that  they  are  more  abundant  under  a  vegetable  diet,  and  disappear 
altogether  under  the  exclusive  use  of  animal  food.  In  man,  under  an 
ordinary  mixed  diet,  they  are  about  one-half  as  abundant  as  the  urates. 

Sodium  Biphosphate. —  This  is  the  ingredient  which  gives  to  the 

*  London  Lancet,  1876.    Vol.  ii.,  p.  848. 


330  FUNCTIONS    OF    NUTRITION. 

urine  its  acid  reaction.  It  is  regarded  as  derived  from  the  sodium 
phosphate  of  the  blood  (Na2H  P04)  by  the  action  of  uric  acid,  which 
unites  with  a  part  of  its  sodium,  forming  sodium  urate,  and  leaving  an 
acid  sodium  phosphate  (NaH2P04).  The  uric  acid  produced  in  the 
system,  though  not  eliminated  in  a  free  form,  causes,  therefore,  indi- 
rectly the  acid  reaction  of  the  urine ;  and  this  reaction  will  vary  in 
intensity  with  the  amount  of  its  production. 

The  Alkaline  Phosphates,  or  phosphates  of  sodium  and  potassium. — 
These  phosphates  exist  in  the  blood  as  well  as  in  the  urine,  and  in 
solution  have  a  mildly  alkaline  reaction.  Owing  to  their  ready  solu- 
bility, they  never  appear  as  a  precipitate,  nor  disturb  in  any  way  the 
transparency  of  the  urine.  It  is  as  a  constituent  of  these  salts  that 
most  of  the  phosphoric  acid  in  combination  is  discharged  with  the  urine. 
According  to  Yogel,  its  excretion  is  increased  by  food  containing  sol- 
uble phosphates  or  substances  capable  of  yielding  phosphoric  acid  in 
the  system.  It  is  accordingly  more  abundant  under  a  diet  of  animal 
food,  less  so  under  a  vegetable  regimen.  It  is  not,  however,  exclu- 
sively derived  from  the  food,  since  it  is  still  discharged,  though  in  dimin- 
ished quantity,  after  long-continued  abstinence.  Its  immediate  origin 
is,  therefore,  wholly  or  partly  from  the  constituents  of  the  body  itself. 
The  observations  of  Wood,*  as  well  as  those  of  Vogel,  show  a  diurnal 
variation  of  considerable  regularity  in  the  excretion  of  the  phosphatic 
salts.  It  is  at  a  minimum  during  the  forenoon,  increases  in  the  latter 
part  of  the  day  after  the  principal  meal,  and  reaches  a  maximum  in  the 
evening  or  during  the  night,  to  diminish  again  on  the  morning  of  the 
following  day.  The  average  quantity  of  the  alkaline  phosphates  dis- 
charged under  an  ordinary  diet  is  a  little  over  four  grammes  per  day. 

The  Earthy  Phosphates,  or  phosphates  of  lime  and  magnesia. — The 
earthy  phosphates  are  usually  excreted  in  much  smaller  quantity  than 
the  preceding.  They  are  held  in  solution  by  the  acid  reaction  of  the 
urine,  and  when  this  reaction  is  absent  or  much  diminished  they  are 
thrown  down  as  a  light  precipitate.  The  neutral  or  faintly  alkaline 
urine,  often  passed  in  the  forenoon,  may  therefore  be  turbid  with  a 
deposit  of  earthy  phosphates,  without  indicating  any  abnormal  increase 
in  their  amount.  According  to  the  observations  of  Wood,  the  alkaline 
and  earthy  phosphates  differ  in  the  conditions  influencing  their  excre- 
tion. During  continued  mental  application,  the  alkaline  phosphates  are 
increased,  while  the  earthy  phosphates  are  diminished ;  the  amount  of 
both  combined  being  not  materially  altered.  The  average  daily  quan- 
tity of  the  earthy  phosphates  is  about  one  gramme,  or  rather  less  than 
one-quarter  that  of  the  alkaline  phosphates. 

Sodium  and  Potassium  Chlorides. — Sodium  chloride,  which  rep- 
resents nearly  the  whole  of  these  salts,  is  by  far  the  most  abundant 
mineral  Ingredient  in  the  urine,  forming  over  one-half  of  its  inorganic 
constituents.  It  is  mainly  derived  from  the  food,  and  is  increased 

*  Proceedings  of  the  Connecticut  Medical  Society,  1869. 


THE    URINE.  331 

or  diminished  according  to  its  amount  in  various  articles  of  diet.  Its 
discharge  is  usually  least  during  the  night,  increases  in  the  forenoon, 
and  is  greatest  during  the  latter  part  of  the  day.  According  to  Vogel,* 
both  mental  and  bodily  exertion  perceptibly  augment  its  excretion; 
and  even  water,  when  taken  in  unusual  quantity,  by  increasing  the 
activity  of  the  kidneys,  causes  a  more  abundant  discharge  of  sodium 
chloride,  subsequently  followed  by  a  corresponding  diminution.  The 
average  amount  of  chlorides  eliminated  with  the  urine  is  about  fifteen 
grammes  per  day. 

Sodium  and  Potassium  Sulphates. — The  sulphates  in  the  urine  are 
derived  partly  from  those  introduced  with  the  food.  Their  quantity 
is  increased  by  the  administration  of  sulphuric  acid  or  of  sodium  sul- 
phate ;  and  the  administration  of  sulphur  or  a  sulphuret  produces  the 
same  effect.  They  are  most  abundant  under  a  diet  of  animal  food, 
owing  to  the  sulphur  contained  in  albuminous  matters,  which  is  finally 
eliminated  in  the  form  of  sulphates.  These  salts  are  freely  soluble  and 
never  appear  as  a  precipitate  in  the  urine.  Their  average  quantity  is 
about  3.96  grammes  per  day. 

Reactions  of  the  Urine  to  Chemical  Tests. 

The  reactions  of  the  urine  to  various  ordinary  tests  form  a  ready  cri- 
terion for  ascertaining  its  normal  or  abnormal  constitution.  The  exact 
quantitative  determination  of  its  ingredients  requires  the  skill  of  the 
professional  chemist ;  but  many  of  its  important  characters  may  be 
recognized  by  simple  means. 

Application  of  Heat. — If  healthy  urine,  of  a  distinctly  acid  reaction, 
be  heated  to  the  boiling  point,  no  change  in  its  appearance  is  produced ; 
but  if  its  acidity  be  very  slight,  it  may  become  turbid  on  boiling,  from 
a  precipitation  of  earthy  phosphates.  These  phosphates  are  less  soluble 
in  a  hot  than  in  a  cold  liquid ;  and  a  faintly  acid  reaction,  which  may 
hold  them  in  solution  at  ordinary  temperatures,  becomes  insufficient 
under  the  application  of  heat,  and  the  phosphates  are  precipitated.  The 
deposit  from  this  cause  is  never  very  abundant,  and  is  at  once  redis- 
solved  by  the  addition  of  any  acid  sufficient  to  restore  the  normal  reac- 
tion of  the  urine.  The  precipitation  of  the  earthy  phosphates  by  boiling 
is,  therefore,  due,  not  to  an  increased  quantity  of  these  salts,  but  to 
deficient  acidity  of  the  urine. 

Diseased  urine  may  become  turbid  on  boiling,  from  the  coagula- 
tion of  albumen.  This  is  distinguished  from  a  precipitation  of  the 
earthy  phosphates  by  two  facts — namely,  first,  that  it  may  take  place 
in  urine  which  is  distinctly  acid  ;  and  second,  that  the  addition  of  nitric 
acid,  which  redissolves  the  phosphatic  precipitate,  only  increases  the 
turbidity  due  to  albumen. 

Acids. — The  addition  of  mineral  acids  to  healthy  urine  produces  no 
immediate  visible  effect,  beyond  increasing  its  acidity  and  slightly  modi- 

*  Analyse  des  Harns.     Wiesbaden,  1872,  p.  350. 


332 


FUNCTIONS    OF    NUTRITION. 


fying  its  color.     They,  however,  decompose  its  urates ;  and  the  uric  acid 

thus  set  free  is  slowly  deposited 
in  the  crystalline  form.  If  ni- 
tric or  hydrochloric  acid  be  added 
to  fresh  filtered  urine,  in  the  pro- 
portion of  about  2  per  cent,  by 
volume,  and  the  mixture  al- 
lowed to  remain  at  rest  for 
twenty-four  hours,  the  sides  and 
bottom  of  the  vessel  become  cov- 
ered with  a  thin  deposit  of  uric 
acid  crystals.  These  crystals 
are  usually  transparent  rhom- 
boidal  plates,  with  their  obtuse 
angles  rounded  off,  and  tinged 
of  a  yellowish  hue  by  the  col- 
oring matter  of  the  urine.  They 

CRYSTALS  OF  URIC  ACID;  deposited  from  urine,  after  are  frequeiltlv  arranged  in  radi- 
the  addition  of  nitric  acid.  J 

ated  clusters,  or  small  spheroi- 
dal masses,  which  vary  in  size  and  regularity,  according  to  the  time 
occupied  in  their  formation. 

When  the  urine  is  scanty  and  concentrated,  with  a  specific  gravity  of 
1030  or  1035,  but  without  abnormal  ingredients,  if  mixed  with  half  its 
volume  of  nitric  acid  and  exposed  to  a  low  temperature,  it  will  soon 
become  filled  with  an  abundant  crystallization  of  nitrate  of  urea.  In 
urine  of  this  specific  gravity,  the  water  is  still  sufficient  to  hold  the  urea 
in  solution,  but  allows  a  separation  of  nitrate  of  urea  on  the  addition  of 
nitric  acid.  This  never  takes  place  in  urine  of  normal  specific  gravity. 

Alkalies. — The  addition  of  an  alkali  or  alkaline  carbonate  to  normal 
urine  diminishes  its  acid  reaction,  and,  when  the  point  of  saturation  is 
reached,  produces  a  turbidity,  owing  to  precipitation  of  the  earthy  phos- 
phates. These  are  the  only  ingredients  of  the  urine  liable  to  be  thrown 
down  by  an  alkali. 

Mineral  Salts. — Solutions  of  barium  chloride,  barium  nitrate,  or  tri- 
basic  lead  acetate,  added  to  healthy  urine,  decompose  its  sulphates,  pro- 
ducing a  dense  precipitate  of  the  corresponding  metallic  salts.  Solu- 
tions of  silver  nitrate  produce  a  precipitate  with  the  sodium  and 
potassium  chlorides,  forming  the  insoluble  silver  chloride.  Tribasic 
lead  acetate  and  silver  nitrate  also  throw  down  mucus  and  coloring 
matters. 

Abnormal  Ingredients  of  the  Urine. 

The  abnormal  ingredients  which  appear  in  the  urine  are  either :  1st. 
Foreign  substances  accidentally  present  in  the  blood  and  eliminated  by 
the  kidneys,  such  ;is  diico.se,  biliary  matters,  medicinal  and  poisonous 
substances;  or  2d.  The  albuminous  constituents  of  the  blood,  discharged 
with  the-  urine  owing  to  disturbance  of  the  renal  circulation. 

Glucose. — The  presence  of  glucose  in  the  urine  is  characteristic  of 


THE    URINE. 


333 


FIG.  81. 


diabetes  mellitus.  In  this  disease  the  urine  is  generally  increased  in 
quantity  and  of  unusually  high  specific  gravity,  namely,  from  1035  to 
1050.  It  is  of  a  light  straw  color,  and  so  transparent  that  it  has  the 
appearance  of  being  dilute,  though 
really  denser  than  usual,  owing  to  the 
glucose  which  it  holds  in  solution.  The 
glucose  may  be  detected  by  Trommer's 
or  Fehling's  test,  or  by  fermentation. 
For  the  latter  purpose  a  little  yeast  is 
mixed  with  15  or  20  times  its  volume 
of  water,  and  the  mixture  allowed  to 
remain  at  rest  in  an  upright  cylindrical 
vessel  until  the  yeast  globules  have 
subsided  to  the  bottom.  The  super- 
natant fluid,  containing  the  soluble 
impurities  of  the  yeast,  is  poured  off, 
and  a  small  quantity  of  the  moist 
deposit  added  to  the  urine.  The  mix- 
ture is  then  placed  in  a  ferment-appa- 
ratus and  kept  at  a  temperature  of 
about  25°  C.,  for  forty-eight  hours, 
when  the  gaseous  products  of  fermen- 
tation will  have  been  completely  dis- 
engaged. The  most  convenient  form 

Of  apparatus    is  a  graduated  test-tube,    FERMENT-APPARATUS,  containing  saccha- 

supported  by  a  foot  and  provided  with 
an  India-rubber  stopper,  through  which 
passes  a  narrow  glass  tube,  open  at 
both  ends.  Its  inner  extremity,  reach- 
ing to  the  bottom  of  the  test-tube,  is 
bent  upward,  to  prevent  the  escape  of  gas,  while  its  outer  portion  is 
bent  downward,  to  allow  the  liquid  expelled  through  it  to  drop  freely 
from  its  orifice.  The  test-tube  being  filled  with  the  fermenting  urine, 
the  disengaged  gas  rises  to  its  upper  part  and  collects  there,  while  the 
urine  is  forced  out  through  the  bent  tube.  Every  cubic  centimetre  of 
carbonic  acid  produced  corresponds  to  0.26  milligrammes  of  sugar 
decomposed.  A  similar  apparatus,  containing  the  same  quantity  of 
healthy  urine  and  yeast,  should  be  kept  at  the  same  temperature  for 
an  equal  time,  as  a  comparative  test;  since  a  small  quantity  of  gas 
might  be  produced  from  the  yeast,  owing  to  its  imperfect  purification. 
But  in  this  case  the  disengagement  of  gas  soon  ceases ;  while  in  the 
fermenting  solution  it  continues  until  all  the  sugar  has  been  decom- 
posed. This  method  does  not  give  the  precise  quantity  of  glucose 
contained  in  any  single  specimen,  since  some  of  the  urine  escapes 
before  fermentation  is  complete  ;  but  it  is  at  the  same  time  the  surest 
indication  of  the  presence  of  sugar,  and  a  ready  means  of  ascertaining 
its  comparative  amount  in  different  specimens. 


rine  urine  in  fermentation.  —  a.  Upper 
part  of  the  test-tube  containing  carbonic 
acid.  b.  Lower  part  of  the  test-tube  con- 
taining the  fermenting  liquid,  c.  Bent 
glass  tube,  to  allow  the  escape  of  liquid. 
d.  Liquid  which  has  been  forced  out  from 
the  test-tube  by  the  accumulation  of  gas. 


334  FUNCTIONS    OF    NUTRITION. 

The  quantity  of  glucose  in  a  given  specimen  may  be  determined 
with  sufficient  accuracy  for  clinical  purposes  by  the  method  of  Rob- 
erts,* which  depends  upon  the  loss  of  specific  gravity  from  the  de- 
composition of  glucose  by  fermentation.  A  portion  of  the  urine  is 
taken  and  its  specific  gravity  ascertained  at  the  temperature  of  25°  C. 
A  little  yeast  is  then  added  and  the  mixture  kept  at  the  same  temper- 
ature until  fermentation  has  ceased ;  when  the  specific  gravity  is  again 
taken.  The  diminution  in  density  caused  by  the  decomposition  of 
glucose  is  such  that  the  loss  of  one  degree  in  specific  gravity  indicates 
the  disappearance  of  2.197  milligrammes  of  glucose  for  every  cubic 
centimetre  of  urine. 

Glucose  can  be  obtained  from  diabetic  urine,  according  to  the  method 
of  Hoppe-Seyler,  by  evaporating  the  urine  over  the  water-bath  to  the 
consistency  of  a  syrup,  and  allowing  it  to  remain  at  rest  until  com- 
pletely crystallized.  The  crystalline  mass  is  triturated  and  washed 
with  a  small  quantity  of  cold  alcohol,  to  remove  the  urea.  The  resi- 
due is  then  extracted  with  boiling  alcohol,  and  the  alcoholic  solution 
filtered  while  hot,  after  which  the  glucose  is  deposited  in  a  crystalline 
form. 

The  glucose  of  diabetic  urine  is  derived  from  the  blood,  from  which 
it  is  eliminated  in  the  renal  circulation.  It  has  been  shown  by  Ber- 
nard^ that  when  glucose  is  injected  into  the  blood-vessels  or  the  sub- 
cutaneous connective  tissue,  the  time  within  which  it  appears  in  the 
urine  varies  with  the  quantity  injected  and  the  rapidity  of  its  absorp- 
tion. If  a  solution  of  one  gramme  of  glucose  in  25  cubic  centimetres 
of  water  be  injected  under  the  skin  of  a  rabbit  weighing  a  little  over 
one  kilogramme,  it  is  destroyed  in  the  circulation,  and  does  not  pass 
out  with  the  urine.  A  dose  of  1.5  gramme,  injected  in  the  same  way, 
appears  in  the  urine  at  the  end  of  two  hours,  2  grammes  in  an  hour 
and  a  half,  2.5  grammes  in  an  hour,  and  12.5  grammes  in  fifteen 
minutes.  When  glucose  accordingly  accumulates  in  the  circulation 
beyond  a  certain  proportion  to  the  volume  of  the  blood,  it  is  elimi- 
nated as  a  foreign  substance,  and  appears  in  the  urine. 

Biliary  Matters. — In  some  cases  of  jaundice,  the  coloring  matter  of 
the  bile  passes  into  the  urine  in  sufficient  abundance  to  give  it  a  deep 
yellow  or  yellowish-brown  tinge.  Sodium  glycocholate  and  tauro- 
cholate,  according  to  Lehmann,  have  also  been  detected  in  the  urine. 
In  these  instances,  the  biliary  matters  are  reabsorbed  from  the  hepatic 
ducts  and  conveyed  by  the  blood  to  the  kidneys. 

Potassium  ferrocyanide,  when  introduced  into  the  circulation,  ap- 
pears with  great  readiness  in  the  urine.  According  to  Bernard,  it  may 
begin  to  be  eliminated  within  twenty  minutes  after  its  injection  into 
the  duct  of  the  submaxillary  gland. 

Iodine,  in  all  its  combinations,  passes  out  by  the  same  channel. 

*  Urinary  and  Renal  Diseases.     Philadelphia  edition,  1872,  p.  198. 

f  Le9ons  de  Physiologic  ExpeVimentale.     Glycoge"nie.     Paris,  1855,  p.  216. 


THE    URINE.  335 

After  the  administration,  in  man,  of  192  milligrammes  of  iodine,  in 
the  form  of  syrup  of  the  iodide  of  iron,  we  have  found  it  in  the  urine 
at  the  end  of  thirty  minutes ;  its  elimination  continuing  for  nearly 
twenty-four  hours.  In  two  patients  who  had  been  taking  potassium 
iodide — one  for  six  weeks,  the  other  for  two  months — the  urine  still  con- 
tained iodine  three  days  after  the  last  dose ;  but  at  the  end  of  three 
days  and  a  half  it  was  no  longer  present.  Iodine,  as  discharged  by 
the  urine,  is  always  in  the  form  of  combination,  from  which  it  must 
be  set  free  by  the  addition  of  a  drop  of  nitric  acid,  after  which  it  pro- 
duces its  characteristic  blue  color  by  admixture  with  starch.  The  same 
is  true  of  other  animal  fluids,  such  as  saliva  and  the  perspiration,  by 
which  iodine  is  also  eliminated  after  its  introduction  into  the  system. 

Quinine,  when  administered  as  a  remedy,  has  been  detected  in  the 
urine.  Ether  passes  out  of  the  circulation  in  the  same  way,  and  its 
odor  is  sometimes  perceptible  in  the  urine,  after  being  inhaled  for  the 
production  of  anesthesia.  The  peculiar  odors  developed  in  the  urine 
after  the  use  of  Asparagus,  and  certain  other  vegetable  substances, 
are  produced  by  a  transformation  of  their  ingredients  while  passing 
through  the  system. 

Albumen. — Under  ordinary  conditions  the  albumen  of  the  blood  does 
not  pass  out  from  the  renal  vessels ;  but  when  the  local  pressure  is 
increased  beyond  a  certain  point,  owing  to  congestion,  compression  of 
the  renal  veins  by  abdominal  tumors,  pregnancy,  or  altered  nutrition  of 
the  kidneys  in  Bright's  disease,  the  albuminous  ingredients  of  the  blood 
transude  through  the  capillaries  and  make  their  appearance  in  the  urine. 

Albuminous  urine  is  usually  pale,  and  often  opalescent  from  the 
admixture  of  exfoliated  epithelium  cells  or  of  fibrinous  casts  from  the 
uriniferous  tubules.  In  these  cases,  it  should  be  rendered  transparent 
by  filtration  before  applying  the  tests,  since  the  turbidity  already  exist- 
ing might  mask  the  reaction  of  albumen,  if  present  in  small  proportion. 

In  albuminous  urine  with  an  acid  reaction,  the  application  of  heat 
produces  a  turbidity  which  is  in  proportion  to  the  quantity  of  albumen 
present.  In  extreme  cases  it  may  solidify,  like  the  serum  of  blood, 
before  reaching  the  boiling  point ;  but  more  frequently  the  albumen  is 
thrown  down  in  loose  whitish  flakes.  When  the  turbidity  produced  by 
boiling  is  moderate  in  amount,  it  may  resemble  that  due  to  precipitation 
of  the  earthy  phosphates.  It  can,  however,  be  distinguished  by  the 
addition  of  a  drop  of  free  acid,  which  at  once  redissolves  the  phosphates, 
but  does  not  affect  a  turbidity  caused  by  albumen.  An  albuminous 
precipitate,  on  the  other  hand,  however  abundant,  is  redissolved  by  the 
addition  of  a  caustic  alkali. 

If  the  urine  be  alkaline  in  reaction,  boiling  may  not  throw  down  its 
albumen,  this  substance  being  soluble  in  an  alkali.  Alkaline  urine, 
accordingly,  if  suspected  of  being  albuminous,  should  be  rendered  dis- 
tinctly acid  before  boiling,  by  the  addition  of  a  small  quantity  of  a  free 
acid. 

Nitric  acid,  added  in  moderate  quantity  to  albuminous  urine,  produces 


336  FUNCTIONS    OF    NUTRITION. 

a  turbidity  by  coagulating  the  albumen.  Alcohol,  in  equal  volume, 
will  have  the  same  effect;  and  a  solution  of  potassium  ferrocyanide, 
acidulated  with  acetic  acid,  will  also  produce  coagulation.  When  all 
these  tests  have  been  applied,  no  doubt  will  remain  as  to  the  presence 
or  absence  of  albumen. 

Deposits  in  the  Urine, 

The  deposits  which  appear  spontaneously  in  the  urine  consist  either : 
1st,  of  some  of  its  normal  ingredients,  thrown  down  in  consequence  of 
a  change  in  its  composition ;  or  2d,  of  exudations  from  the  urinary 
passages,  owing  to  diseased  local  conditions.  Those  belonging  to  the 
first  class  are  the  earthy  phosphates  and  the  urates.  The  most  common 
of  those  belonging  to  the  second  are  blood,  mucus,  and  pus. 

Deposits  of  the  Earthy  Phosphates. — These  deposits  are  always  of  a 
white  color,  and  are  seldom  abundant.  When  the  urine  is  first  passed, 
they  are  disseminated  through  its  mass  in  the  form  of  a  light  cloudiness, 
which  settles  slowly  to  the  bottom  of  the  vessel.  The  urine  is  alkaline 
or  neutral  in  reaction,  and  is  usually  of  less  than  the  average  specific 
gravity.  The  precipitate  is  amorphous,  presenting  no  crystalline  forms 
under  the  microscope.  It  is  at  once  redissolved  on  the  addition  of  an 
acid,  and  presents  all  the  chemical  reactions  belonging  to  the  earthy 
phosphates.  The  alkaline  condition  of  the  urine,  causing  this  deposit, 
may  be  due  to  temporary  diminution  in  the  quantity  of  uric  acid  pro- 
duced in  the  system,  or  to  a  formation  of  alkaline  carbonates  from  the 
use  of  fruits  or  vegetables  containing  salts  of  the  vegetable  acids. 

Deposits  of  the  Urates.  —  The  urates  appear  as  a  deposit  when  their 
formation  in  the  system  is  unusually  abundant  in  proportion  to  the 
urine,  so  that  they  are  no  longer  held  in  solution.  The  urine  is  nearly 
always  concentrated,  highly  colored,  above  the  average  specific  gravity, 
and  of  a  strongly  acid  reaction.  The  deposit  is  sometimes  nearly  white, 
but  usually  of  a  light  pink  or  even  red  color,  according  to  the  concen- 
tration of  the  urine.  If  allowed  to  settle  in  a  white  porcelain  vessel, 
and  the  supernatant  fluid  poured  off,  the  deposit  is  sometimes  left  as  a 
brick-red  stain  on  the  inner  surface  of  the  vessel,  forming  what  is  known 
as  the  "brick-dust"  sediment. 

Deposits  of  the  urates  are  recognized  by  the  two  following  characters, 
First,  they  never  appear  while  the  urine  is  still  warm,  but  only  after  it 
has  cooled  ;  the  urine,  when  first  passed,  being  always  perfectly  clear, 
and  becoming  turbid  on  repose.  Secondly,  the  urine,  however  turbid, 
if  heated  in  a  test-tube,  becomes  again  clear,  usually  before  reaching  the 
boiling  point.  Both  these  characters  depend  on  the  solubility  of  the 
urates  at  high  temperatures. 

In  rare  cases,  when  urine  is  turbid  with  the  urates  and  also  contains 
albumen,  a  double  effect  may  be  produced  by  the  application  of  heat. 
When  the  specimen  is  first  heated,  it  clears  up,  owing  to  the  solution 
of  the  urates;  but,  on  approaching  the  boiling  point,  it  again  becomes 
t  iirl)i(l  from  precipitation  of  the  albumen. 


THE    URINE. 


337 


FIG.  82. 


The  urates  are  also  soluble  in  caustic  alkalies,  and  the  addition  of 
a  few  drops  of  a  solution  of  sodium  or  potassium  hydrate  redissolves 
the  precipitate.  Free  acids,  on  the  other  hand,  decompose  it,  with  the 
formation  of  a  corresponding  sodium  or  potassium  salt,  which  remains 
in  solution,  and  the  separation  of  uric  acid,  which  slowly  crystallizes. 
But  the  volume  of  uric  acid  produced  is  so  much  smaller  than  that 
of  the  urates  previously  disseminated  through  the  urine,  that  the  only 
effect  immediately  apparent  is 
that  of  solution  of  the  precipi- 
tate. A  deposit  of  the  urates  is 
accordingly  the  only  one  liable 
to  occur  in  the  urine,  which  is 
cleared  up  by  both  alkalies  and 
acids. 

Deposits  of  the  urates,  when 
first  thrown  down,  are  pulveru- 
lent in  form,  presenting  under 
the  microscope  the  appearance 
of  minute  granules.  After  a  day 
or  two  they  sometimes  crystal- 
lize in  globular  masses  of  radi- 
ating needles,  often  with  straight 
or  curved  projections  from  the 
outer  surface.  If  a  free  acid  be 
added  to  this  deposit,  the  crys- 
talline masses  grow  transparent,  and  slowly  dissolve  from  without 
inward,  while  rhomboidal  tabular  crystals  of  uric  acid  appear  in  the 
adjacent  fluid. 

Crystals  of  uric  acid  sometimes  appear  in  a  deposit  of  the  urates 
after  a  few  hours,  owing  to  the  development  of  a  free  acid  in  the  urine  ; 
and  they  are  sometimes  formed  within  the  urinary  passages,  so  as  to  be 
present  in  the  urine  when  passed.  Owing  to  their  density  and  angu- 
larity they  cause  an  irritation  to  the  mucous  membrane  of  the  bladder 
and  urethra,  and  are  known  as  the  "gravel"  of  the  urine.  In  a 
mingled  precipitate  of  the  urates  and  uric  acid,  the  uric  acid  is  a  scanty, 
dense,  deeply  colored,  crystalline  deposit  which  sinks  rapidly  and  accu- 
mulates at  the  bottom  of  the  vessel,  while  the  comparatively  light  and 
pulverulent  urates  are  more  slowly  deposited  above  it. 

Blood. — Urine  containing  blood  is  more  or  less  tinged  throughout 
with  a  dull  reddish  color.  After  one  or  two  hours  of  repose  in  a  cylin- 
drical vessel,  the  blood-globules  are  slowly  deposited ;  and  the  minute 
filamentous  coagula  with  which  they  are  frequently  entangled  form  a 
strongly  colored  red  layer  at  the  bottom  of  the  vessel.  The  nature  of 
the  deposit  is  recognized  by  two  well-marked  characters,  namely :  1st. 
The  blood-globules  are  distinguished  by  microscopic  examination,  their 
form  not  being  entirely  lost  even  after  remaining  in  the  urine  for  sev- 

W 


CRYSTALLINE  MASSES  OF  SODIUM  URATE,  from 
a  urinary  deposit. 


FUNCTIONS    OF    NUTRITION. 


hours;  and  2d.  The  supernatant  fluid,  when  decanted,  is  found  to 
contain  albumen. 

Mucus.  —  The  slight  quantity  of  vesical  mucus,  normally  contained 
in  the  urine,  is  at  first  uniformly  disseminated  throughout  its  mass,  and 
even  after  being  left  in  repose  is  insufficient  to  produce  any  well-marked 
or  consistent  deposit.  The  light  cloudy  opalescence,  which  it  forms  at 
the  bottom  of  the  vessel,  is  visible  only  on  close  inspection,  and  is  read- 
ily disseminated  airain  by  agitation.  But  in  inflammation  of  the  uri- 
nary bladder,  the  mucus  is  increased  in  quantity  and  altered  in  quality. 
It  then  appears  as  a  consistent  mass,  which  does  not  mix  uniformly 
with  the  urine,  but  subsides  to  the  bottom  as  a  semifluid  deposit,  Mucus 
by  itself  is  transparent  and  colorless,  but  it  frequently  contains  epithe- 
lium cells  from  the  bladder  ;  and  when  crystalline  or  pulverulent  deposits 
take  place  in  the  urine,  they  first  appear  in  contact  with  the  mucus,  90 
that  its  surface  is  often  sprinkled  with  the  urates  or  phosphates.  A 
deposit  of  mucus  is  distinguished  by  its  viscid  and  semifluid  consistency. 
It  is  not  affected  by  heat,  but  is  coagulated  and  shrivelled  by  alcohol 
and  by  nitric  or  acetic  acid.  Urine  containing  mucus  is  liable  to  rapid 
decomposition,  and  often  has  a  peculiarly  offensive  odor  from  this  cause. 

Pus.  —  When  pus  is  contained  in  the  urine  it  gradually  subsides  if 
allowed  to  remain  at  rest,  forming  a  dense,  creamy-white  deposit,  per- 
fectly fluid  in  consistency  and  easily  disseminated  by  agitation.  Micro- 
scopic examination  shows  it  to  be  composed  of  colorless,  granular,  nucle- 
ated "pus-globules,"  identical  in  appearance  with  the  white  globules  of 
the  blood,  but  distinguishable  from  those  belonging  to  a  deposit  of  blood 
by  their  abundance  and  by  the  absence  of  red  globules.  If  the  super- 
natant fluid  be  poured  off,  and  a  few  drops  of  a  solution  of  caustic  alkali 
added  to  the  deposit,  it  loses  its  white  color  and  opacity,  owing  to  the 
solution  of  its  granular  cells,  and  swells  up  into  a  transparent,  colorless 
gelatinous  substance,  which  can  no  longer  be  poured  off  in  drops,  but 
slides  out  of  the  vessel  in  a  single  semi-solid  mass.  This  character  will 
serve  to  distinguish  a  purulent  deposit  from  any  other  liable  to  occur 
in  the  urine.  The  supernatant  urine,  when  filtered,  is  found  to  contain 
a  small  quantity  of  albumen,  the  interstitial  fluid  of  pus  being  itself 
albuminous. 

Decomposition  of  the  Urine. 

After  its  discharge  from  the  body,  the  urine  undergoes  spontaneous 
changes,  by  which  its  organic  ingredients  are  altered  and  finally  disap- 
pear. This  decomposition  is  closely  dependent  on  the  mucus  in  the 
urine,  bring  much  retarded  if  this  be  separated  by  immediate  filtrntioii, 
and  hastened  in  a  corresponding  degree  when  the  mucus  is  abnormally 
abundant.  It  is  characterized  by  two  different  stages,  distinguished  by 
the  successive  development  of  acid  and  alkaline  products.  They  are 
known  respectively  as  the  acid  and  the  alkaline  fermentations. 

Acid  Fermentation  of  the  Urine.  —  This  process  takes  place  for  t  In- 
most part  within  twelve,  twenty-lour,  or  forty-eiirht  hours  after  the  dis- 
charge of  the  urine.  It  consists  in  the  product  ion  of  a  free  acid,  usually 


THE    URINE. 


339 


lactic  acid,  from  some  undetermined  organic  ingredients  of  the  excretion. 
The  urine  when  fresh  contains  no  free  acid,  its  reaction  being  due  to  the 
presence  of  sodium  biphosphate.  But  lactic  acid  has  so  often  been  found 
in  urine  as  to  be  sometimes  regarded  as  one  of  its  normal  constituents. 
Observation,  however,  has  shown  that  urine,  though  free  from  lactic  acid 
when  first  passed,  may  present  distinct  traces  of  this  substance  after 
some  hours  of  exposure  to  the  air.  Its  production  in  this  way,  though 
not  constant,  appears  sufficiently  frequent  to  be  regarded  as  a  normal 
process. 

There  is  reason  to  believe  that  oxalic  acid  is  sometimes  produced  in  a 
similar  manner.  A  deposit  of  lime  oxalate  is  frequently  present  in  the 
urine  a  day  or  two  after  its  discharge,  without  the  existence  of  any  per- 
ceptible morbid  symptom.  Whenever  oxalic  acid  is  formed  in  the  urine 
it  unites  with  lime  in  preference  to  any  other  of  the  bases  present,  and 
is  consequently  deposited  under  the  form  of  lime  oxalate,  which  is 
quite  insoluble  in  urine,  even  at  the  boiling  point.  In  these  cases,  the 
lime  oxalate  crystals  gradually  appear  in  the  light  cloud  of  mucus  at 
the  bottom  of  the  vessel.  They  are  of  minute  size,  for  the  most  part 
just  visible  to  the  naked  eye,  scanty  in  amount,  transparent,  and  color- 
less. They  have  the  form  of  regular  octohedra,  or  double  quadrangular 
pyramids,  united  base  to  base.  They  usually  show  themselves  about 
the  second  day,  the  urine  continuing  clear  and  retaining  its  acid  reac- 
tion ;  and  they  frequently  appear  as  a  deposit  when  no  substance  con- 
taining oxalic  acid  or  oxalates  has  been  taken  with  the  food.  The  precise 
source  of  the  oxalic  acid,  under 
these  circumstances,  has  not 
been  determined,  but  it  is  prob- 
ably derived  from  a  partial  meta- 
morphosis of  the  uric  acid.  If 
uric  acid  be  boiled  in  two  parts 
of  water  with  lead  peroxide,  it 
is  decomposed,  with  the  produc- 
tion, among  other  substances, 
of  oxalic  acid ;  and  it  is  supposed 
that  some  similar  change  may 
take  place  in  the  urine,  causing 
the  appearance  of  oxalic  acid  in 
minute  quantity.  This  decom- 
poses a  portion  of  the  lime  salts, 
and  consequently  appears  as  a 

Crystalline    deposit   Of    lime    OX-  CRYSTALS  OF  LIME  OXALATE,  deposited  from  healthy 

urine,  during  the  acid  fermentation. 

alate. 

Alkaline  Fermentation  of  the  Urine. — After  a  few  days  the  changes 
above  described  come  to  an  end,  and  are  succeeded  by  the  transformation 
of  urea  into  ammonium  carbonate.  This  change,  which  may  be  artifi- 
cially produced  in  a  watery  solution  of  urea  by  continued  boiling,  takes 
place  in  the  urine  slowly  at  low  temperatures,  more  rapidly  during  warm 


FIG.  83. 


340 


FUNCTIONS    OF    NUTRITION. 


weather.     The  elements  of  two  molecules  of  water  unite  with  those  of 
urea  to  produce  ammonium  carbonate,  as  follows : 


Urea. 
CH4N20  + 


Ammonium  carbonate. 


iMLO         = 


Fro.  84. 


The  ammoniacal  salt  when  first  produced  neutralizes  a  corresponding 
quantity  of  sodium  biphosphate,  diminishing  the  acid  reaction  of  the 
urine.  This  diminution  continues,  as  the  fermentation  proceeds,  until 
the  acidity  disappears  altogether.  The  urine  then  becomes  neutral, 

and  subsequently  alkaline  ;  its 
alkalescence  growing  more  pro- 
nounced with  the  accumulation 
of  the  ammoniacal  salt. 

The  time  at  which  the  urine 
becomes  alkaline  varies  with  its 
original  degree  of  acidity  and 
the  rapidity  of  its  decomposi- 
tion. Urine  which  is  neutral 
at  the  time  of  its  discharge, 
becomes  alkaline  more  rapidly 
than  that  which  has  at  first  a 
strongly  acid  reaction.  In  sum- 
mer, it  is  often  alkaline  on  the 
third,  fourth,  or  fifth  day;  while 
in  winter,  if  kept  in  a  cool  place, 

CRYSTALS  OF  AMMONIO-MAUNESIAN    PHOSPHATE,    it    may   still    be    neutral    at    the 

healtby  Ur"'C'  dU"°g  ""  a'kalil 


end  of  fifteen  days.  In  paraly- 
sis  of  the  bladder  with  cystitis, 

where  the  vesical  mucus  is  increased  in  quantity  and  altered  in  quality, 
and  the  urine  remains  in  the  bladder  for  ten  or  twelve  hours  at  the 
temperature  of  the  body,  it  may  be  distinctly  alkaline  and  ammoniacal 
at  the  time  of  its  discharge.  In  these  cases  it  is  acid  when  secreted, 
but  becomes  alkaline  while  retained  in  the  bladder. 

The  first  effect  of  the  alkaline  condition  of  the  urine,  thus  produced, 
is  a  precipitation  of  the  earthy  phosphates.  This  deposit  slowly  settles 
on  the  sides  and  bottom  of  the  vessel,  or  is  partly  entangled  with  certain 
animal  matters,  forming  a  thin,  opaline  scum  on  the  surface.  There  an- 
no crystals  at  this  time,  the  deposit  being  entirely  amorphous  and  gran- 
ular. 

The  next  change  is  the  production  of  a  new  salt,  the  ammonio-mag- 
nesian  phosphate,  by  the  combination  of  ammonia,  formed  from  urea, 
with  the  magnesium  phosphate  already  present  in  the  urine.  This 
change  is  represented  as  follows  : 


Magnesium  phosphate.  Ammonia. 

M-IIP04  +  Ml., 


Anmioiiii.-niairnrsian  phosphate. 

MgNH«PO« 


The  crystals  of  tins  salt  show  themselves  throughout  all  parts  of 
the  mixture,  entanirled    in    the   mucus  at    the   bottom,  adhering  to  the 


THE    URINE. 


341 


sides  of  the  vessel,  and  scattered  over  the  film  on  the  surface  of  the 
urine.  By  their  refractive  power  they  give  to  this  film  a  glistening 
and  iridescent  appearance,  nearly  always  visible  at  the  end  of  six  or 
seven  days.  They  are  colorless,  transparent,  triangular  prisms,  gener- 
ally with  bevelled  extremities,  their  edges  and  angles  frequently  re- 
placed by  secondary  facets.  They  are  insoluble  in  alkalies,  but  are 
easily  dissolved  by  acids,  oven  very  dilute.  At  first  they  are  of 
minute  size,  but  gradually  increase,  so  that  after  seven  or  eight  days 
they  may  be  recognized  by  the  naked  eye. 

As  decomposition  proceeds,  the  ammonium  carbonate,  after  saturating 
all  the  other  ingredients  with  which  it  is  capable  of  uniting,  begins  to 
be  given  off  in  a  free  form.  The  urine  then  acquires  an  ammoniacal 
odor ;  and  a  piece  of  moistened  test-paper,  held  above  its  surface,  will 
be  turned  by  the  escaping  alkaline  gas.  This  is  the  source  of  the 
ammoniacal  vapor  given  off  wherever  urine  is  allowed  to  remain  and 
decompose.  The  change  continues  until  all  the  urea  has  disappeared. 


SECTION  III. 

THE  NERVOUS   SYSTEM. 


CHAPTER    I. 

GENERAL    STRUCTURE   AND    FUNCTIONS    OF 
THE   NERVOUS   SYSTEM. 

THE  nervous  system  is  an  apparatus  of  communication,  by  which 
the  various  parts  of  the  body  are  brought  into  relation  with  each 
other,  and  different  organs  excited  to  harmonious  or  alternating  action. 
Its  effects  are  produced  by  an  influence  transmitted  from  one  region  to 
another,  stimulating  or  modifying  the  animal  functions  according  to 
the  requirements  of  the  system  at  large.  It  differs  in  its  properties 
and  mode  of  action  from  the  other  anatomical  structures  of  the  body, 
to  which  it  is  superadded  for  their  regulation  and  control. 

The  specific  physiological  properties  or  modes  of  activity,  belonging 
to  a  bodily  organ,  may  often  be  called  into  operation  by  a  direct 
stimulus  or  exciting  cause.  The  poles  of  a  galvanic  battery,  applied 
to  the  muscles  of  a  frog's  amputated  leg,  produce  contraction  and  move- 
ment ;  a  solution  of  atropine  dropped  on  the  cornea  of  a  living  animal, 
when  absorbed  and  brought  in  contact  with  the  iris,  causes  a  change 
in  the  condition  of  its  fibres  and  a  dilatation  of  the  pupil ;  and  if  the 
heart  of  a  frog,  after  removal  from  the  body,  be  touched  with  the  point 
of  a  needle,  it  repeats  the  movement  of  an  ordinary  pulsation.  In 
these  instances,  the  physiological  act  is  in  response  to  a  stimulus  oper- 
ating directly  on  the  tissues  of  the  organ. 

But  this  is  not  the  mode  in  which  the  animal  functions  are  excited 
during  life.  The  stimulus  which  calls  into  action  the  living  organs 
is  not  direct,  but  indirect,  in  its  operation.  In  the  normal  condition, 
the  muscles  are  never  made  to  contract  by  an  external  stimulus  applied 
to  their  own  fibres,  but  by  one  which  operates  on  some  other  organ, 
adjacent  or  remote.  The  functional  activity  of  the  glands  is  increased 
or  diminished  by  causes  acting  on  other  parts;  as  where  a  flow  of 
saliva  from  the  parotid  is  produced  by  food  introduced  into  the  mouth, 
or  where  the  cutaneous  perspiration  is  modified  by  mental  conditions. 
Tim  various  organs  are  thus  connected  with  each  other  by  a  mutual 
sympathy  which  regulates  their  physiological  action  ;  and  this  eonnec- 
tion  is  established  by  inniiis  of  (lie  nervous  system. 

342 


GENERAL    STRUCTURE    OF    THE    NERVOUS    SYSTEM.     343 

The  function  of  the  nervous  system  is  therefore  to  associate  the  dif- 
ferent parts  of  the  body  in  such  a  manner,  that  stimulus  applied  to 
one  organ  may  excite  the  activity  of  another. 

The  instances  of  this  action  are  almost  as  numerous  as  the  vital 
phenomena.  The  light  falling  upon  the  retina  produces  contraction 
of  the  pupil.  Introduction  of  food  into  the  stomach  causes  a  discharge 
of  bile  from  the  gall-bladder.  Alimentary  substances,  in  contact  with 
the  mucous  membrane  of  the  intestine,  excite  the  peristaltic  action 
of  its  muscular  coat ;  and  the  presence  of  a  foetus  in  the  uterus  is 
accompanied  by  increased  growth  of  the  mammary  glands.  Every 
organ  is  subservient,  in  the  manifestation  of  its  activity,  to  influences 
derived  from  other  parts  through  the  nervous  system. 

In  the  nervous  system  there  are  two  kinds  of  anatomical  elements ; 
namely,  nerve  fibres  and  nerve  cells.  The  nerve  fibres  are  the  charac- 
teristic constituents  of  the  "  white  substance,"  forming  the  mass  of 
the  nerves  and  their  ramifications,  the  external  portion  of  the  spinal 
cord,  and  much  of  the  internal  parts  of  the  brain.  The  nerve  cells  are 
found  in  the  "  gray  substance,"  which  constitutes  the  external  or  con- 
voluted layer  of  the  brain,  as  well  as  various  internal  deposits  near  its 
base,  the  central  portions  of  the  spinal  cord,  and  many  small  detached 
masses,  or  ganglia,  in  different  parts  of  the  body. 

Nerve  Fibres. 

The  nerve  fibres  are  cylindrical  filaments,  arranged  in  bundles  or 
tracts,  for  the  most  part  parallel  with  each  other.  Their  diameter 
varies  considerably,  even  in  the  same  locality ;  some  of  the  fibres  in  a 
single  bundle  being  10,  15,  or  18  micro-millimetres  in  diameter,  while 
others  are  not  more  than  2.5  mmm.  Their  average  size  also  varies  in 
different  parts  of  the  nervous  system.  The  larger  fibres  -are  found  in 
the  peripheral  trunks  and  branches  of  the  nerves,  where  they  have  an 
average  diameter  of  12.5  mmm. ;  in  the  white  substance  of  the  brain 
and  spinal  cord  their  average  diameter  is  5  mmm.,  and  in  the  gray 
substance  it  is  reduced  to  2  mmm.  Certain  portions  of  the  nervous 
system  are  distinguished  by  the  comparative  abundance  of  their  larger 
or  smaller  fibres.  Thus  in  the  cutaneous  nerves  of  man,  according  to 
Bidder,  Volkmann,  and  Kolliker,  the  larger  and  smaller  fibres  are  in 
about  equal  quantity,  while  in  the  muscular  nerves  the  larger  fibres  are 
three  times  as  abundant  as  the  smaller.  In  the  nerves  of  bony  tissue 
the  number  of  small  fibres  is  double  that  of  the  large  ones;  and  in  the 
gray  substance  of  the  cerebral  hemispheres  they  all  belong  to  the 
smaller  variety,  none  being  larger  than  6  or  7  mmm.  in  diameter. 
The  nerve  fibres  in  the  same  bundle  or  tract  may  increase  or  diminish 
in  size  at  different  parts  of  their  course ;  as  Kolliker  has  shown  that 
the  fibres  of  the  posterior  roots  of  the  spinal  nerves,  in  passing  to  the 
gray  substance  of  the  cord,  are  reduced  in  average  diameter  from  1 0 
to  5  mmm.,  and  those  of  the  white  substance  of  the  cerebral  hemi- 


344  THE    NERVOUS    SYSTEM. 

spheres,  on  entering  the  gray  matter  of  the  convolutions,  are  reduced 
from  5  to  2  mmm.  in  diameter. 

The  nerve  fibre,  in  its  most  complete  form,  presents  three  distinct 
structural  elements,  namely :  an  external  tubular  sheath,  an  interme- 
diate medullary  layer,  and  a  central  axis  cylinder. 

The  Tubular  Sheath. — The  nerve  fibre  consists  externally  of  a  col- 
orless, transparent,  tubular  membrane,  known  as  the  "  sheath  of 
Schwann,"  which  closely  invests  its  remaining  portions.  This  mem- 
brane may  often  be  distinguished  at  points  where  the  fibre  has  been 
accidentally  compressed  or  indented ;  or  it  may  be  brought  into  view 
according  to  the  method  of  Kolliker,  by  treating  the  fibres  with  a  cold 
solution  of  sodium  hydrate,  and  afterward  boiling  them  for  an  instant 
in  the  same  fluid.  This  extracts  the  greater  part  of  their  contents,  and 
leaves  the  sheath  in  the  form  of  an  empty  cylindrical  canal.  In  its 
general  character,  the  tubular  sheath  resembles  the  sarcolemma  of 
muscular  fibre,  its  principal  physical  properties  being  its  cohesion  and 
elasticity.  .  Its  office  is  no  doubt  that  of  a  protecting  envelope,  by 
which  the  internal  portions  are  maintained  in  the  cylindrical  form. 

The  Medullary  Layer. — Immediately  within  the  tubular  sheath  is 
a  layer  of  transparent,  highly  refractive  material,  nearly  oleaginous  in 
consistency,  termed  the  "medullary  layer,"  or  myeline,  which  gives 
to  the  nerve  fibres,  and  the  tracts  composed  of  them,  their  white 
glistening  aspect.  Owing  to  the  presence  of  this  substance,  the  nerve 
fibre  has,  under  the  microscope,  a  characteristic  double  contour,  pre- 
senting two  parallel  outlines  on  each  border ;  indicating  the  external 
and  internal  limits  of  the  medullary  layer.  The  fibres  containing  a 
medullary  layer,  and  exhibiting  its  characteristic  double  contour,  arc 
called  "medullated  nerve  fibres." 

The  medullary  layer  is  readily  altered  by  the  imbibition  of  water. 
It  swells  up  and  exudes  from  the  divided  extremities  of  the  ner\<> 
fibres,  in  filamentous  tufts  and  masses  of  irregular  outline,  which  from 
their  peculiar  appearance  are  known  as  " myeline  forms."  These  m, 
become  mingled  with  each  other  when  a  number  of  divided  or  lacerated 
nerve  fibres  have  been  placed  in  water;  and  the  myeline  is  after  a  time 
so  much  altered  and  distorted,  by  the  imbibition  extending  to  the  in- 
terior of  the  fibre,  as  to  obscure  all  its  remaining  anatomical  characters. 
Owing  to  this  alterability  of  the  nerve  fibres  it  has  hern  found  of 
advantage  to  study  them  with  the  aid  of  various  staining  and  harden- 
ing liquids;  one  of  the  most  useful  of  which  is  perosmic  acid.  Dilute 
solutions  of  this  substance  fix  the  nerve  fibres  in  their  natural  form 
and  position,  so  that  they  can  afterward  be  manipulated  with  less 
danger  of  injury;  and  it  moreover  stains  the  medullary  layer  of  a 
blackish  hue,  without  coloring  the  remain  ing  elements.  When  a  group 
of  nerve  fibres,  stained  by  perosmic  acid,  are  viewed  in  trans\ 
section,  each  fibre  appears  as  a  dark  zone  enclosing  a  transparent,  col- 
orless space  near  its  centre;  the  dark  exterior  zone  being  the  blackened 
medullary  layer,  while  the  central  spare  represents  the  nneoloivd  axis 


GENERAL   STRUCTURE    OF    THE    NERVOUS    SYSTEM.     345 


FIG.  85. 


cylinder.  When  viewed  in  profile,  such  fibres  exhibit  a  dark  colored 
double  border,  formed  by  the  medullary  layer,  surrounding  the  longi- 
tudinal axis  cylinder. 

In  regard  to  its  physiological  function,  the 
medullary  layer  is  considered  by  some  writers 
as  an  isolating  substance,  like  the  gutta-percha 
envelope  of  a  submarine  telegraph  wire,  to  con- 
fine the  transmission  of  nerve  force  within  proper 
limits,  and  prevent  its  diffusion  to  neighboring 
parts.  It  certainly  does  not  act  directly  in  this 
transmission ;  since,  as  hereafter  shown,  it  is 
interrupted  at  numerous  points  in  the  course  of 
the  fibres ;  and  it  is  always  wanting  for  some 
distance  in  the  neighborhood  of  both  their 
origin  and  their  termination.  These  facts  are 
also  at  variance  with  its  supposed  character  as 
an  isolating  material ;  since  any  discontinuity  of 
its  substance  would  seem  to  destroy  its  efficiency 
for  that  purpose.  It  is  sometimes  regarded,  with 
perhaps  greater  plausibility,  as  affording,  by  its 
consistency,  a  physical  protection  to  the  axis 
cylinder;  securing  it  from  local  injury,  in  flexions 
or  indentations,  by  the  uniform  support  which  a 
fluid  envelope  would  give.  Its  interruptions 
during  the  course  of  the  nerve  fibres  are  not 
sufficient  to  interfere  with  its  usefulness  in  this 
respect. 

The  A.ris  Cylinder. — The  central  part  of  the 
nerve  fibre  consists  of  a  pale,  homogeneous,  or  finely  granular  cord,  of 
nearly  cylindrical  form,  situated  in  its  longitudinal  axis.  From  these 
characters  it  has  received  the  name  of  the  "  axis  cylinder."  In  consist- 
ency the  axis  cylinder  is  a  soft  solid,  and,  though  very  delicate,  it  has 
a  certain  degree  of  elasticity.  By  some  observers  (Schultze,  Gerlach) 
it  is  regarded  as  composed  of  minute  fibrilla3,  united  into  a  uniform 
bundle ;  by  others  of  equal  authority  (Kolliker)  the  indications  of  its 
fibrillated  constitution  are  considered  as  uncertain. 

The  axis  cylinder  consists  of  an  albumenoid  substance,  insoluble  in 
water,  alcohol,  and  ether.  It  becomes  pale  and  swollen  by  the  action 
of  concentrated  acetic  acid,  and  is  readily  dissolved  by  a  boiling  solution 
of  sodium  hydrate.  It  is  stained  red  by  solutions  of  carmine,  which,  on 
the  other  hand,  produce  no  effect  on  the  medullary  layer ;  and  after  the 
use  of  this  agent,  the  transverse  section  of  a  nerve  shows  in  the  interior 
of  each  fibre  a  red  or  pinkish  spot  in  the  place  of  the  axis  cylinder, 
surrounded  by  a  colorless  zone  representing  the  medullary  layer.  In 
nerve  fibres  treated  with  a  solution  of  gold  chloride  and  subsequently 
exposed  to  light,  the  axis  cylinder  is  stained  of  a  dark  purple,  nearly 
black  color ;  and  by  this  mode  of  preparation  nerve  fibres  of  extreme 


NERVE  FLBRKS,  fixed  and 
stained  by  perosmic  acid ; 
from  the  posterior  wall  of 
dorsal  lymph-sac  of  Frog. 
—1,  1,  Medullary  layer. 
2,  Axis  Cylinder.  3, 3,  Con- 
strictions of  Ranvier.  4, 4, 
Incisions  of  Schmidt. 


346  THE    NERVOUS    SYSTEM. 

delicacy  may  be  traced  where  they  would  otherwise  escape  observa- 
tion. 

In  its  physiological  properties,  the  axis  cylinder  is  beyond  question 
the  essential  element  of  the  nerve  fibre.  By  its  abundant  albumenoid 
ingredients  it  is  distinguished  from  the  medullary  layer,  and  it  forms 
exclusively  the  whole  of  the  fibre  both  at  its  origin  and  its  termina- 
tion. It  is  no  doubt  through  the  axis  cylinder  that  the  nerve  current 
is  transmitted,  the  remaining  portions  of  the  fibre  being  of  secondary 
importance. 

Of  the  three  constituent  parts  of  the  nerve  fibre,  the  axis  cylinder  is 
the  only  one  uniformly  continuous  throughout.  At  frequent  intervals 
in  its  course  the  fibre  presents  a  remarkable  diminution  in  size,  caused 
by  an  annular  constriction  of  the  sheath  of  Schwann  and  an  interruption 
at  the  same  point  of  the  medullary  layer  (Fig.  85:,.3).  These  constric- 
tions, which,  from  the  name  of  their  discoverer,  are  known  as  the 
"  constrictions  of  Ranvier,"  recur  in  general  at  distances  of  about  75  or 
80  times  the  diameter  of  the  nerve  fibre.  At  each  of  these  points  the 
sheath  of  Schwann  contracts  to  about  one-half  its  ordinary  calibre, 
leaving  a  diminished  orifice  through  which  the  axis  cylinder  passes, 
while  the  medullary  layer  terminates  on  each  side  by  a  rounded 
extremity.  The  portion  of  a  nerve  fibre  included  between  two  con- 
secutive annular  constrictions,  is  called  an  "  inter-annular  segment.'1 

The  annular  constrictions  visible  in  nerve  fibres  have  been  often 
attributed  to  mechanical  injury,  or  to  the  action  of  fluids  used  in  their 
preparation ;  but,  as  Ranvier  has  shown,  they  may  be  seen,  without 
the  addition  of  any  reagent,  in  the  uninjured  nerve  fibres  of  the  frog's 
lung,  while  the  circulation  of  the  blood  is  still  going  on.  They  are 
consequently  a  normal  anatomical  feature  of  the  nerve  fibre. 

Beside  the  annular  constrictions,  there  are  other  partial  or  complete 
interruptions  of  the  medullary  layer,  of  more  frequent  occurrence,  situ- 
ated at  irregular  intervals  in  the  length  of  each  inter-annular  segment. 
These  are  the  ''incisions  of  Schmidt"  (Fig.  854f4).  In  a  profile  view 
of  the  nerve  fibre  they  present  the  appearance  of  narrow  oblique  cuts 
in  the  medullary  layer,  extending  from  its  outer  surface  nearly  or  quite 
to  its  internal  border.  Both  the  annular  constrictions  and  the  incisions 
of  Schmidt  are  most  distinctly  recognized  after  partial  staining  of  the 
medullary  layer  with  perosmic  acid. 

Non-medullated  Nerve  Fibres.  —  Beside  the  nerve  fibres  above 
described,  there  is  a  second  variety,  distinguished  by  the  absence  of 
a  medullary  layer,  and  termed  "non-me<lnllated  nerve  fibres."  Tiny 
are  the  only  nerve  fibres  to  be  found  in  invertebrate  animals;  and 
in  man  and  the  vertebrate  animals  they  are  mingled  in  various 
proportions  with  inediillated  fibres  in  different  nerves.  The  olfac- 
tory nerve  consists  exclusively  of  non-inednllated  fibres;  there  are 
none,  on  the  other  hand,  in  the  optic  nerve,  which  is  composed  alto- 
gether of  the  medullaled  variety.  Among  the  peripheral  nerves, 
non-inednllated  fibres  are  most  abundant  in  those  of  the  sympathetic 


GENERAL   STRUCTURE    OF    THE    NERVOUS    SYSTEM.     347 


FIG.  86. 


system,  where  they  were  first  discovered,  and  where  they  often  consti- 
tute a  majority  of  all  the  nerve  fibres  present.  In  the  trunks  and 
branches  of  the  cerebro-spinal  system  they  are  much  less  numerous, 
but  vary  in  proportion  in  different  nerves  and  in  different  species  of 
animals.  In  all  cases,  nerves  consisting  mainly  or  exclusively  of  medul- 
lated  fibres  have  an  opaque,  white,  glistening  aspect,  due  to  their  mye- 
line ;  while  those  containing  non-medullated  fibres  are  grayish  or  semi- 
transparent,  according  to  the  proportion  of  these  fibres  in  their  tissue. 

All  the  medullated  nerve  fibres  lose  their  myeline  and  become  non- 
medullated  shortly  before  their  termination  in  the  muscular  tissue  or 
the  organs  of  sensibility ;  and  they  are  also  non-medullated  at  and  near 
their  termination  in  the  gray  matter  of  the  brain  and  spinal  cord.  In 
these  situations  the  nerve  fibre  is  reduced  to  a  simple  axis  cylinder,  by 
which  it  is  connected  with  the  peripheral  and  central  organs  of  the 
nervous  system. 

Course  and  Mutual  Relation  of  the  Nerve  Fibres. — In  the  white 
substance  of  the  brain  and  spinal  cord  the  nerve  fibres  form  continuous 
tracts,  lying  in  close  apposition  with 
each  other,  enveloped  only  by  a  deli- 
cate granular  and  finely  fibrillated 
intervening  material.  But  on  emerg- 
ing from  the  bony  cavities  of  the 
cranium  and  vertebral  canal,  they 
arc  collected  into  distinct  bundles, 
each  invested  by  a  lamellated  sheath 
of  fibrous  connective  tissue,  and  en- 
closed in  a  larger  compound  mass  by 
a  common  fibrous  sheath  or  "  neuri- 
lemma."  Such  a  compound  bundle 
is  called  a  nerve,  and  the  fibres  which 
it  contains  are  distributed,  after  a 
longer  or  shorter  transit,  usually  to 
associated  organs  or  adjacent  regions 
of  the  body. 

So  far  as  our  observation  extends, 
the  individual  nerve  fibres,  as  a  rule, 
are  continuous  and  independent,  from 
their  origin  in  the  nervous  centres  to 
'within  a  short  distance  of  their  pe- 
ripheral termination.  When  a  nerve 
divides  into  several  branches,  or 
when  adjacent  nerves  communicate 
by  inosculation,  as  in  the  cervical, 
brachial,  or  lumbar  plexuses,  it  is  because  certain  fibres  leave  those 
with  which  they  were  associated  and  pursue  a  different  course.  A 
nerve  which  originates,  for  example,  from  the  spinal  cord,  and  passes 
do\vn  the  arm  to  the  muscles  and  integument  of  the  hand,  contains  at 


DIVISION  OF  A  NERVOUS  BRANCH  (a),  into  its 
ultimate  fibres,  b,  c,  d,  e. 


348  THE    NERVOUS    SYSTEM. 

its  origin  all  or  nearly  all  the  fibres,  which  it  afterward  gives  off  in 
branches  and  ramifications ;  and  the  inosculation  of  two  nerves  is 
effected  by  some  of  the  fibres  from  one  passing  over  to  join  the  other, 
while  some  of  those  belonging  to  the  second  may  also  cross  and  join 
the  first.  In  whatever  way,  therefore,  the  nerve  fibres  are  associated 
in  the  trunks  and  branches,  each  may  still  preserve  its  specific  and  inde- 
pendent action. 

A  nerve  usually  consists  of  several  distinct  bundles  of  fibres,  each 
bundle  enveloped  in  its  lamellated  sheath ;  and  when  the  bundle,  after 
its  separation  from  the  trunk,  divides  into  secondary  branches,  each 
branch  is  covered  by  a  thinner  lamellated  sheath,  an  offshoot  from  that 
of  the  parent  bundle.  These  sheaths  are  lined  by  a  layer  of  flattened 
polygonal  endothelial  cells,  like  those  on  the  inner  surface  of  the  blood- 
vessels. As  the  branches  are  reduced  in  size  by  repeated  subdivision, 
their  sheaths  become  thinner  in  the  same  proportion,  by  a  diminution 
in  the  number  of  lamellae  of  which  they  are  composed ;  and  in  those 
containing  but  few  nerve  fibres,  the  sheath  consists  of  a  single  endo- 
thelial layer.  This  transparent  envelope,  surrounding  the  smallest  rami- 
fications of  the  nerves,  is  known,  from  the  name  of  its  discoverer,  as 
the  "sheath  of  Henle."  Each  individual  nerve  fibre,  after  separating 
from  the  rest,  to  run  an  independent  course,  is  also  accompanied  by 
such  a  sheath,  of  about  double  its  own  diameter,  in  which  it  lies,  sur- 
rounded by  lymph  or  a  lymph-like  fluid. 

An  isolated  nerve  fibre,  passing  through  the  tissues  toward  its  termi- 
nation, is  therefore  covered  by  two  envelopes,  quite  distinct  from  each 
other.  One  is  its  tubular  membrane,  or  "  sheath  of  Schwann,"  which 
is  part  of  the  fibre  and  closely  invests  its  surface;  the  other  is  the 
"sheath  of  Henle,"  which  is  an  adventitious  tube,  of  larger  size,  and 
separated  from  it  by  an  appreciable  space. 

Peripheral  Termination  of  the  Nerve  Fibres. — Near  their  peripheral 
termination,  the  nerve  fibres  present  certain  important  modifications 
both  in  structure  and  arrangement. 

First,  the  smaller  branches,  or  bundles  of  nerve  fibres,  after  penetra- 
ting the  tissues,  suddenly  divide  and  subdivide  with  unusual  rapidity ; 
and  these  subdivisions,  uniting  with  each  other  by  inosculation,  form 
plexuses,  from  which  are  given  off  individual  fibres  to  supply  the  ana- 
tomical elements  of  the  tissues.  In  the  skin  there  are  two  such  plex- 
uses, a  deeper  and  a  more  superficial,  of  which  the  latter  is  the  more 
closely  set  and  composed  of  smaller  bundles,  containing  only  one  or 
two  fibres  each.  As  a  rule,  in  all  tissues,  the  second  or  terminal  plexus 
is  the  finest,  inclosing  between  its  meshes  the  narrowest  interspaces. 
The  nerve  fibres,  on  reaching  the  terminal  plexus,  are  also  reduced  in 
si/e,  being  diminished  both  in  the  skin  and  in  tin-  muscles  from  10  or 
15  mmm.  to  4  or  5  mmm.  in  diameter.  According  to  Kollikcr  it  is 
sometimes  possible  to  observe  a  diminution  in  size  of  single  nerve 
fibres  in  different  parts  of  the  muscular  tissue. 

Secondly,  both  in  the  terminal  plexus  and  in  the  launches  given  off 


GENERAL    STRUCTURE    OF   THE    NERVOUS    SYSTEM.      349 


FIG.  87, 


from  them,  the  nerve  fibres  themselves  undergo  division ;  so  that  a 
single  fibre  in  this  situation  may  give  rise  to  two  or  more  branches, 
each  branch  retaining  all  the  original  anatomical  characters  of  the  nerve 
fibre.  Such  a  division  of  nerve  fibres,  according  to  Ranvier,*  is  occa- 
sionally visible  in  the  smaller  trunks  and  branches,  as  in  those  of  the 
spleen  and  even  sometimes  in  the  muscular  nerves ; 
but  in  general  it  only  occurs  in  the  immediate  neigh- 
borhood of  their  final  distribution.  Here,  on  the  other 
hand,  it  is  very  frequent.  The  division  always  takes 
place  at  an  annular  constriction.  The  axis  cylinder 
divides,  usually  at  an  acute  angle,  into  two  or  more 
secondary  axis  cylinders,  each  of  which  becomes  at 
once  enveloped  by  a  medullary  layer,  like  that  above 
the  constriction  ;  and  each  secondary  nerve  fibre  is  at 
first  nearly  or  quite  equal  in  diameter  to  that  from 
which  it  was  derived.  But  after  several  successive 
divisions  the  fibres  are  diminished  in  average  di- 
ameter ;  and  at  the  same  time  the  annular  constric- 
tions are  more  frequently  repeated.  In  the  small 
nerve  fibres,  accordingly,  near  their  peripheral  termi- 
nation, the  inter-annular  segments  are  shorter  and 
more  numerous  than  in  the  large  fibres  of  the  ner- 
vous trunks  and  branches. 

A  nerve  fibre  may  thus  pass  undivided  throughout 
the  roots,  trunk,  and  principal  branches  and  ramifica-  DIVISION  OF  A  NERV1, 
tions  of  the  nerve,  and  may  then,  shortly  before  its 
termination,  break  up  into  a  number  of  separate  but 
closely  adjacent  secondary  fibres.  It  has  been  esti- 
mated by  Reichert,  that,  in  the  subcutaneous  muscles  of  the  frog,  one 
primitive  fibre  may  give  rise  by  its  division  to  about  30  terminal 
extremities. 

Thirdly,  the  nerve  fibre,  near  its  peripheral  extremity,  loses  its  medul- 
lary layer,  and,  consequently,  its  double  contour.  As  the  sheath  of 
Schwann  also  disappears,  the  nerve  fibre  finally  consists  only  of  the 
axis  cylinder,  which  near  its  extreme  point  of  termination  sometimes 
exhibits  a  fine  longitudinal  striation,  indicating  the  existence  of  minute 
fibrillae  united  with  each  other. 

The  termination  of  nerves  in  the  sensitive  integument  has  been 
most  successfully  studied  in  the  "  Pacinian  bodies  "  of  the  skin  and 
mesentery,  and  in  the  "  end-bulbs "  of  the  conjunctiva.  In  these 
bodies,  both  in  man  and  animals,  there  is  a  general  resemblance  in 
the  arrangement  of  the  parts,  together  with  variations  of  detail  in  dif- 
ferent species  and  different  situations.  They  all  consist  of  an  ovoidal- 
shaped  mass,  surrounded  by  single  or  multiple  capsules,  which  are 
expansions  of  the  larnellated  sheath  of  the  nerve  branch  supplying  them, 
or  of  the  sheath  of  Henle  accompanying  its  finest  ramifications.  They 

*  Histologie  du  Systeme  Nerveux.     Paris,  1878,  tome  ii.,  pp.  109,  268. 


FIBRK;  from  pulmo- 
nary membrane  of 
frog's  lung. 


350  T  J I  K    NERVOUS    S  Y  S  T  E  M  . 

contain  a  fluid  or  semifluid  interstitial  substance,  in  which  the  terminal 
nerve  fibre  is  enclosed  and  in  which  it  ends,  either  by  expansion  into 
the  so-called  "  terminal  buds,"  or  by  the  indefinite  disappearance  of  its 
fibrillae. 

The  Pacinian  bodies  of  the  hands  and  feet  in  man,  and  in  correspond- 
ing situations  in  many  of  the  quadrupeds,  are  from  1  to  4.5  millimetres 
in  length.  Their  substance  is  enclosed  in  numerous  concentric  cap- 
sules, each  of  which,  according  to  Key  and  Retzius,*  is  a  continuation 
of  the  lamellated  sheath  of  the  nerve-branch,  and  is  furnished  with  a 
double  layer  of  polygonal  nucleated  endothelial  cells,  like  those  in  the 
lamellated  sheath  itself.  Afa  the  central  part  of  the  Pacinian  body  the 
j,  capsules  are  absent,  leaving  a  narrow  elon- 

gated space,  known  as  the  "  interior  bulb," 
surrounded  by  an  endothelial  layer  continuous 
R5^HHG9&       with  that  of  the  sheath  of  Henle.     Into  this 
jls||l|      interior  bulb  the  ultimate  nerve  fibre  pene- 
fl  trates,  often  after  repeated  division  of  its  parent 

*  i 

fibre,  and  at  the  same  time  becomes  divested 
of  its  medullary  layer.  The  cylinder  axis  then 
runs  longitudinally  through  the  central  part 
of  the  interior  bulb  toward  its  peripheral  ex- 

BBBH  H  RS  tremity,  where  it  exhibits  a  fibrillated  appear- 
'i  i:n-HKRAL  EXTRKMITY  OF  THE  ance,  and  ends  in  one  or  more  fungus-like  tufts, 
INTERIOR  BULB  OF  A  PACINIAN  or  "terminal  buds  "  which  appear  like  radiated 

BODY;  showing  the  fibrillated  .  . 

texture  of  the  axis  cylinder  and   expansions  of  its  Component  fibnllse. 

bUd8'  (Key  ^  The  end-bulbs  in  the  conjunctiva  are  similar 
in  form  to  the  Pacinian  bodies,  but  of  much 
smaller  size,  measuring  in  man  from  one-third  to  one-half  a  millimetre 
in  length.  They  have  only  a  single  capsule,  continuous  with  the  sheath 
of  Henle  accompanying  the  nerve  fibre.  The  nerve  fibre,  as  in  the  fore- 
going description,  loses  its  medullary  layer  after  reaching  the  base  of 
the  bulb,  and  enters  its  interior  as  a  pale,  slender  axis  cylinder.  In  the 
calf,  the  axis  cylinder  sometimes  runs  nearly  straight  through  the  bull) 
toward  its  farther  extremity,  where  it  terminates  in  a  fungus-like  tuft, 
like  those  of  a  Pacinian  body.  In  man,  it  makes  a  number  of  turns 
within  the  bulb,  where  it  finally  disappears,  apparently  by  dispersion 
of  its  fibrillaj. 

The  termination  of  nerve  fibres  in  muscular  tissue  has  boon  studied 
in  many  animals,  both  in  the  fresh  condition  and  with  the  aid  of  stain- 
ing and  hardening  preparations.  No  one  of  these  methods  has  been 
found  to  demonstrate  fully  the  anatomical  features  of  the  nervous  ter- 
mination; but  by  combining  the  results  obtained  from  all,  histologists 
have  acquired  a  certain  degree  of  knowledge  in  this  respect,  which  may 
lie  summed  up  as  follows.  In  general,  a  striped  muscular  fibre  is  sup- 
plied with  only  a  single  ultimate  nerve  fibre;  but  this  nerve  fibre,  on 

*  Anatomic  dt-s  Nc-rvunsystems  und  ik-s  Bindegewebes,  Stockholm,  1870.  Zweite 
Hiill'tu,  p.  17G. 


FIG.  89. 


OENERAT,    STRUCTURE    OF    THE    NERVOUS    SYSTEM.     351 

passing-  beneath  the  sarcolemma,  divides  into  a  terminal  arborization, 
which  lies  in  contact  with  the  striated  muscular  surface.  The  stimulus 
conveyed  through  a  single  nerve  fibre  is  thus 
communicated  to  the  contractile  substance  of 
the  muscle  at  many  different  points.  With  the 
exception  of  some  variations  of  form  in  differ- 
ent species,  the  details  of  the  muscular  termi- 
nation of  nerve  fibres  are  essentially  the  same 
in  reptiles,  birds,  and  mammalians.  As  the 
ultimate  nerve  fibre  reaches  the  point  of  its 
attachment  to  the  muscle,  the  sheath  of  Henle, 
with  which  it  was  surrounded,  leaves  it  and 
becomes  continuous  with  the  sarcolemma.  At 
the  same  time  its  medullary  layer  terminates, 
in  the  usual  way,  at  an  annular  constriction. 
That  portion  of  the  nerve  fibre  immediately 
outside  the  sarcolemma  is  its  last  inter-annu- 
lar segment ;  and  within  the  sarcolemma  the 
axis  cylinder  is  destitute  of  myeline.  At  this 
situation  the  axis  cylinder  breaks  up  into  its 
terminal  arborization ;  and  it  is  the  form, 
direction,  and  frequency  of  these  ramifications 
which  constitute  the  main  differences  in  this 
respect  between  different  animals.  Each  mem- 
ber of  the  terminal  arborization  is  surrounded 
by  a  light  zone  of  granular  matter,  in  which 
large  flat  oval  nuclei,  with  well-marked  nu- 
cleoli,  are  imbedded.  The  only  parts  of  the 
nerve  fibre  therefore  in  immediate  contact 
with  the  contractile  muscular  substance  are 
those  derived  from  the  ramification  of  its  axis 
cylinder. 

Physiological  Properties  of  the  Nerve  Fibres. 
— The  nerve  fibres  are  channels  of  communica- 
tion between  the  nervous  centres  on  the  one 
hand  and  the  peripheral  organs  on  the  other. 
For  this  purpose  they  are  endowed  with  a 
special  irritability  by  which,  when  excited  at 
one  end,  they  transmit  the  impulse  throughout 
their  entire  length,  and  produce  an  effect  at 
the  opposite  extremity.  Those  distributed  to  _ 

^\  .    *  SENSITIVE    NERVE   FIBRE   AND 

the  skin,  when  excited  at  the  periphery,  pro-     END-BULB;  from  the  conjunc- 
duce  in  the  brain  a  corresponding  sensation.     tivaofman-  The  turns  of  the 

axis  cylinder,  within  the  bulb, 

On  the  other  hand,  those  distributed  to  the     are  exhibited  in  various  trans- 
muscles,  When   excited    at   their   Oriffin   by  the      verse  and  oblique  sections.  (Key 

J  and  Retzius.) 

impulse  of  the  will,  cause  contraction  in  the 

muscular  fibres.     This  action  produces  no  visible  change  in  the  nerve 


352  THE    NERVOUS    SYSTEM. 

fibre,  its  effects  being  manifest  only  in  the  organs  where  it  terminates. 
Nevertheless,  it  is  evident  that  the  fibre  serves  to  communicate  in 
some  way  an  action  from  one  extremity  to  the  other ;  since,  if  it  be 
divided  in  any  part  of  its  course,  the  communication  ceases,  and  sensa- 
tion can  no  longer  be  perceived  from  iin- 
pressions  made  on  the  skin,  nor  voluntary 
contraction  excited  in  the  muscles. 

Owing  to  the  different  effects  thus  pro- 
duced at  their  extremities,  the  nerves  and 
nerve  fibres  are  distinguished  by  different 
names.  Those  which  transmit  the  stimu- 
lus of  sensation,  from  the  periphery  to 
the  centre,  are  called  sensitive  nerves  or 
nerve  fibres;  those  which  transmit  the 
stimulus  of  motion,  from  the  nervous 
centre  to  the  muscles,  are  called  motor 
nerves  or  nerve  fibres.  As  a  rule,  both 
sensitive  and  motor  fibres  are  associated 
in  the  same  bundle,  and  separate  from 
each  other  only  near  their  final  distribu- 
tion. But  in  some  situations,  near  the 
origin  of  the  nerves  as  well  as  near  their 
termination,  the  sensitive  and  motor  fibres 
run  in  distinct  bundles :  as,  for  example, 

NERVOUS  TERMINATION  IN  A  Muscu-    .      ,.  „  ,,       „„.,  „  .   , 

LAR  FIBRE  OF  THE  GREEN  LIZARD,  in  the  two  roots  of  the  fifth  pair  of  cranial 
—A,  sheath  of  Henie,  surrounding  nerves,  and  in  those  of  the  spinal  nerves 

the  nerve  fibre.  6,  Annular  constric-  .,,  „,        ,,,  ,     ,          .  ., 

tion,  and  division  of  the  nerve  fibre,  generally.     The  fibres  belonging  to  the 
m.  Last  interaunuiar  segment   r,  facial  nerve  are  all  motor  fibres,  making 

Terminal  arborization  of  axis  cylin-    , ,  .  ,      .      ,  m, 

der  beneath  the  sarcolemma.    (Ran-    this    exclusively   a    motor    nerve.       Those 

vier-)  branches  of  the  fifth  pair,  on  the  other 

hand,  which  are  distributed  to  the  integument  and  mucous  membranes 
of  the  face,  are  exclusively  sensitive;  while  the  branch  of  the  s;i un- 
nerve distributed  to  the  muscles  of  mastication  consists  principally  or 
entirely  of  motor  fibres. 

No  essential  distinction  is  perceptible,  in  anatomical  characters,  be- 
tween sensitive  and  motor  nerve  fibres.  In  nerves  which  perform  a 
motor  function,  the  fibres  are  for  the  most  part  of  comparatively  lar^-e 
size,  averaging  15  mmm.  in  diameter;  while  in  those  performing  u 
sensitive  function  they  are  smaller,  averaging  not  more  than  10  mm  m. 
in  diameter,  and  many  of  them  being  considerably  less.  But  this  is 
only  a  difference  of  numerical  proportion  between  the  larger  and  smaller 
fibres;  since  both  large  and  small  fibres  are  found  in  both  motor  and 
sensitive  nerves.  Even  the  motor  fibres  become  reduced  to  the  smaller 
size  before  terminating  in  the  muscular  tissue ;  and  the  nerve  fibres 
generally  are  diminished  or  increased  in  diameter  on  passing  into  or 
out  of  the  gray  substance  of  the  nervous  centres.  No  absolute  dis- 
tinction therefore  can  be  made  between  sensitive  and  motor  fibres  as 


GENERAL   STRUCTURE    OF   THE    NERVOUS   SYSTEM.     353 

regards  their  size;  and  in  the  essential  details  of  their  structure, 
namely,  the  tubular  sheath,  the  medullary  layer,  and  the  axis  cylinder, 
they  are  to  all  appearance  completely  identical. 

Degeneration  and  Regeneration  of  Divided  Nerves. — The  imme- 
diate effect  of  dividing  nerve  fibres  is  to  suspend  their  function.  The 
communication  between  their  extremities  being  cut  off,  the  sensitive 
fibres  can  no  longer  transmit  an  impression  from  the  skin  to  the 
nervous  centre,  and  the  motor  fibres  can  no  longer  convey  a  stimulus 
of  motion  from  the  nervous  centre  to  the  muscles.  This  paralysis  of 
motion  and  sensibility  follows  instantaneously  upon  the  division  of 
the  nerve  fibres. 

But  in  addition  to  this  result  there  also  takes  place,  in  the  separated 
portion  of  the  nerve,  a  structural  degeneration  of  its  fibres.  The  first 
indication  of  this  change  is  visible  in  the  medullary  layer.  It  divides, 
in  the  course  of  each  interannular  segment,  into  two,  three,  or  four 
distinct  masses,  the  intervals  between  which  are  occupied,  according 
to  Ranvier,*  by  a  new  growth  of  nearly  transparent,  finely  granular 
albuminous  matter  from  the  inner  surface  of  the  sheath  of  Schwann ; 
which  is  already  sufficient,  in  the  rabbit,  at  the  end  of  forty-eight 
hours,  to  fill  at  certain  points  the  whole  calibre  of  the  sheath.  The 
division  of  the  medullary  layer  goes  on  until  it  is  entirely  broken  up 
into  globular  masses  of  varying  size,  scattered  irregularly  through  the 
substance  of  the  fibre,  and  completely  obscuring  its  normal  structure. 
By  this  process,  the  continuity  of  the  medullary  layer  is  destroyed,  its 
myeline  being  reduced  to  the  condition  of  isolated  oily-looking  drops, 
and  gradually  transformed  into  a  diffused  granular  mixture.  Finally, 
the  granules  themselves  disappear,  and  the  tubular  sheath,  partially 
emptied  by  the  atrophy  of  the  medullary  layer,  becomes  collapsed  and 
wrinkled.  Owing  to  the  disappearance  of  the  myeline,  the  nerve  loses 
its  white  glistening  aspect  and  assumes  a  grayish  hue.  According  to 
the  testimony  of  all  recent  observers,  degeneration  goes  on  at  the 
same  time  in  the  axis  cylinder.  This  portion  of  the  fibre  is  enveloped 
and  encroached  upon  by  the  growth  of  new  matter,  its  continuity  is 
broken  at  various  points,  its  separated  fragments  are  bent  or  folded 
upon  themselves,  and  at  last  can  no  longer  be  made  visible  by  the 
staining  action  of  a  carmine  solution.  Thus  all  the  structural  elements 
of  the  nerve  fibre,  excepting  the  sheath  of  Schwann,  undergo  a  degen- 
eration which  results  in  complete  atrophy. 

The  rapidity  with  which  this  change  takes  place  varies  with  the 
species  and  age  of  the  animal.  It  is  less  rapid  in  the  cold-blooded, 
more  so  in  the  warm-blooded  species.  It  goes  on  more  quickly  in  the 
young,  more  slowly  in  full-grown  animals.  According  to  Vulpian,  in 
young  dogs,  as  a  rule,  the  disappearance  of  the  medullary  layer  is 
complete  in  six  weeks  or  two  months  from  the  date  of  the  injury. 

The  degeneration  of  the  fibres  of  a  divided  nerve,  whether  sensitive 


*  Histologie  du  Systeme  Nerveux.     Paris,  1878,  tome  L,  p.  315. 

X 


THE    NERVOUS    SYSTEM. 

or  motor,  extends  throughout  their  entire  length  beyond  the  point  of 
division  to  their  peripheral  terminations.  Vulpian*  found  that  in 
dogs,  six  weeks  after  division  of  the  sciatic  nerve,  no  unaltered  nerve 
fibres  could  be  discovered  in  the  muscles  of  the  corresponding  foot. 
According  to  the  same  observer,  the  alteration  is  simultaneous,  or 
nearly  so,  in  all  parts  of  the  nerve  beyond  its  division ;  being  no 
further  advanced  near  the  point  of  section  than  toward  the  periphery. 
If  there  be  any  difference  in  this  respect,  the  degeneration  appears  to 
be  more  rapid  at  the  terminal  extremity  of  the  nerve ;  since,  in  the 
experiments  of  Ranvier,  on  the  rabbit,  forty-eight  hours  after  division 
of  the  sciatic  nerve,  its  terminal  fibres  in  the  muscles  of  the  leg  con- 
tained only  separate  masses  of  myeline  in  the  form  of  oily  drops. 

The  degeneration  of  divided  nerve  fibres  involves  the  loss  of  their 
physiological  properties.  Immediately  after  the  division  of  a  motor 
nerve,  the  resulting  paralysis  is  due  only  to  its  local  discontinuity  at 
the  point  of  section,  which  arrests  the  passage  of  a  nervous  stimulus 
coming  from  the  brain ;  and  a  galvanic  current  applied  to  the  nerve 
below  its  division  will  still  produce  contraction  in  the  muscles  to  which 
it  is  distributed.  So  long  as  this  can  be  done,  it  shows  that  the  nerve, 
though  separated  from  the  central  parts,  still  retains  its  irritability, 
and  is  capable  of  responding  to  a  stimulus  by  muscular  action.  But 
after  a  time  this  property  disappears.  In  the  rabbit,  the  irritability 
of  a  divided  nerve  is  lost  in  forty-eight  hours,  in  the  pigeon  at  the  end 
of  three  days,  and  in  the  dog  at  the  end  of  four  days ;  while  in  the 
frog  it  persists  more  or  less  for  thirty  days.  These  variations  corre- 
spond with  the  rapidity  of  degeneration  in  the  nerve  fibres ;  and  by 
comparative  observations  on  different  animals,  Ranvier  has  shown  that 
in  all  cases  the  disappearance  of  irritability  of  the  nerve  corresponds 
in  time  with  the  loss  of  continuity  in  the  axis  cylinder.  This  cor- 
roborates a  conclusion  derived  from  other  sources,  namely,  that  the 
axis  cylinder  is  the  essential  element  of  the  nerve  fibre,  through  which 
its  physiological  action  is  transmitted. 

A  nerve,  accordingly,  some  days  after  its  division,  has  lost  both  its 
physiological  properties  and  its  anatomical  structure.  It  can  no  longer 
convey  sensitive  impressions  from  the  integument,  and  it  is  incapable 
of  exciting  muscular  contraction.  But  this  loss  of  function  is  not 
permanent.  After  a  time  the  divided  nerve  may  reunite,  and  its 
power  of  communication  may  be  restored.  This  is  shown,  not  only 
by  the  consolidation  of  its  divided  extremities  and  the  reappearance 
of  its  normal  physical  aspect,  but  also  by  the  reestablishment  of  its 
functions.  The  portions  of  integument  which  had  lost  their  sensi- 
bility again  become  sensitive  to  external  impressions,  and  the  power 
of  voluntary  motion  returns  in  the  paralyzed  muscles.  This  takes 
place  by  a  regeneration  of  nerve  fibres  in  the  affected  nerve  beyond 
the  point  of  division.  All  observers  are  now  agreed  that  the  nerve 

*  Le9ons  8ur  la  Physiologic  du  Syst&ne  Nerveux.     Paris,  1866,  p.  1M.J. 


GENERAL    STRUCTURE    OF    THE    NERVOUS    SYSTEM.     355 

fibres  thus  produced  are  fibres  of  new  formation.  The  old  fibres  have 
completely  disappeared  throughout  the  peripheral  ramifications  of  the 
nerve,  and  their  place  is  taken  by  others  of  subsequent  growth. 

The  details  of  this  regeneration  are  not  fully  known ;  but  its  essen- 
tial characters,  so  far  as  they  have  been  ascertained,  are  as  follows : 
The  new  fibres  begin  to  show  themselves  in  the  divided  nerve  before 
the  complete  disappearance  of  the  old  medullary  granules.  They  are 
always  smaller  than  the  average  size,  and  their  interannular  segments 
are  shorter  than  in  the  fully  developed  condition ;  but  in  other  respects 
their  structure  is  normal,  and  even  when  very  slender  they  exhibit 
annular  constrictions,  and  a  distinct  medullary  layer,  capable  of  being 
stained  by  perosmic  acid.  They  gradually  increase  in  diameter,  and 
in  the  thickness  of  their  medullary  layer ;  and  when  the  process  of 
regeneration  is  complete,  the  nerve  again  presents  its  normal  whiteness 
and  opacity. 

There  is  some  uncertainty  as  to  the  direction  in  which  the  growth 
of  new  fibres  takes  place.  By  several  histologists  it  is  maintained  that 
the  regenerated  axis  cylinders  are  offshoots  from  those  in  the  central 
undegenerated  extremity  of  the  nerve  ;  their  growth  extending  thence 
into  the  peripheral  portions.  But  this  opinion  is  based  only  on  analogy, 
from  a  similar  growth  of  embryonic  nerve  fibres  in  the  tail-membrane 
of  the  tadpole,  and  does  not  rest  on  any  certain  results  of  direct  obser- 
vation. It  is  possible  that  the  new  fibres  may  grow  simultaneously 
throughout  the  separated  portion  of  the  nerve,  increasing  everywhere 
in  development  until  their  normal  structure  is  attained.  From  numer- 
ous observations  on  this  subject,  it  was  the  conclusion  of  Vulpian* 
that  the  regeneration  of  the  fibres  at  any  given  time  is  the  same  at  all 
points  in  the  separated  portion  of  a  divided  nerve.  Vulpian  and  Philip- 
peaux  have  also  found  that  if  the  hypoglossal  or  the  lingual  nerve  be 
divided,  and  the  central  portion  extracted,  so  that  no  communication 
can  be  reestablished  with  the  nervous  centres,  the  peripheral  portion 
may  be  regenerated  in  the  usual  manner,  notwithstanding  its  perma- 
nent separation  from  the  central  extremity.  This  would  show  that  the 
power  of  regeneration  resides  in  the  nerve  itself,  the  materials  being 
supplied  by  the  nutritive  plasma  of  its  own  tissues. 

The  rapidity  of  regeneration  in  the  fibres  of  a  divided  nerve,  and 
the  length  of  an  excised  portion  which  may  be  restored,  vary  with  the 
age  and  species  of  the  animal.  According  to  Ranvier,  after  simple 
division  of  a  nerve,  in  the  rabbit,  regeneration  is  in  full  progress  at  the 
end  of  nine  or  ten  weeks,  though  many  of  the  new  fibres  are  of  less 
than  the  average  diameter.  Yulpian  found,  in  very  young  animals,  a 
loss  of  nerve  substance,  from  one  to  two  centimetres  in  length,  restored 
at  the  end  of  six  weeks ;  and  in  young  rats  a  portion  of  the  sciatic 
nerve  six  millimetres  long  was  reproduced  in  seventeen  days.  .In 
adult  animals,  and  especially  in  man,  the  restoration  of  divided  nerves 

*  Lefons  sur  la  Physiologic  du  Systeme  Nerveux.     Paris,  1866,  p.  258. 


356 


THE    NERVOUS    SYSTEM. 


FIG.  91. 


is  much  less  rapid.  When  small  nervous  branches  supplying  the  skin 
have  been  cut,  the  loss  of  tactile  sensibility  in  the  immediate  neighbor- 
hood often  persists  for  weeks  or  months  after  the  healing  of  the  wound. 
Restoration  may  sometimes  take  place  in  larger  nerves,  as  in  a  case 
reported  by  L'Etievant,*  where  the  median  nerve,  in  a  man  twenty-six 
years  of  age,  was  divided  at  the  upper  third  of  the  arm.  The  power  of 
motion  and  sensibility,  in  the  parts  supplied  by  this  nerve,  remained 
abolished  for  ten  months,  but  began  to  reappear  in  fourteen  months, 
and  were  nearly  restored  at  the  end  of  a  year  and  a  half.  But  accord- 
ing to  both  L'Etievant  and  Mitchell,  f  when  the  injured  nerves  in  man 
are  of  considerable  size,  the  restoration  of  function,  as  a  general  rule, 
is  either  very  imperfect  or  does  not  take  place  at  all. 

Nerve  Cells. 

The  nerve  cells,  the  characteristic  anatomical  element  of  the  gray 
substance,  are  irregularly  rounded  bodies,  consisting  of  a  soft,  nearly 
transparent,  finely  granular,  albuminous  matter,  with  a  large,  distinctly 
marked  nucleus  and  nucleolus.  They  often  contain  in  addition  yellow- 
ish-brown pigment  grains,  imbedded  in  the  substance  of  the  cell.  They 

vary  in  size  in  different  regions.  The 
smaller  cells,  from  10  to  20  mmm.  in 
diameter,  are  found  in  the  ganglia  of 
the  sympathetic  system,  parts  of  the 
cerebral  hemispheres,  and  the  posterior 
horns  of  gray  matter  in  the  spinal  cord. 
The  larger,  from  40  to  60  mmm.,  are  in 
the  cerebellum  and  the  medulla  oblon- 
gata ;  and  the  largest  of  all  are  in  the 
anterior  horns  of  gray  matter  of  the 
spinal  cord,  where  they  sometimes  reach 
the  diameter  of  130  or  135  mmm.,  or 
seventeen  times  the  size  of  the  red 
globules  of  the  blood. 

The  nerve  cells  are  especially  distin- 
guished by  their  processes.  These  are 
narrow  offshoots  from  the  body  of  the 
cell,  consisting  apparently  of  the  same 
finely  granular  albuminous  material. 
Their  number  varies  in  different  parts.  In  the  Gasserian  ganglion  and 
the  spinal  ganglia  of  man,  as  well  as  in  those  of  the  dog,  cat,  rabbit, 
and  frog,  the  nerve  cells  have  each  only  a  single  process.  In  the 
sympathetic  ganglia  in  man  they  have  several ;  and  in  the  gray  sub- 
stance of  the  brain,  medulla  oblongata,  and  spinal  cord  each  cell  presents 
from  three  or  four  to  seven  or  eight  processes,  running  in  various 


NSEVK  CELLS,  from  the  anterior  horn  of 
gray  substance  of  the  spinal  cord. 


*  Tr:iit6  des  Sections  Nervcuses.     Paris,  1873,  p.  ">4. 

f  Injuries  of  Nerves,  and  their  Consequences.     Philadelphia,  1874,  p.  84. 


GENERAL   STRUCTURE    OF    THE    NERVOUS    SYSTEM.     357 


FIG.  92. 


directions.  At  a  certain  distance  from  their  origin,  the  processes  are 
often  branched,  the  branches  again  dividing  and  subdividing  until 
reduced  to  a  ramification  of  slender  filaments.  But  in  many  instances, 
on  the  other  hand,  the  cell-process  extends  for  a  considerable  distance 
without  division,  as  a  nearly  cylindrical  or  flattened  filament,  similar 
in  appearance  to  the  axis  cylinder  of  a  nerve  fibre. 

Each  nerve  cell,  in  its  normal  situation,  is  contained  in  a  sheath  or 
capsule,  consisting  of  a  thin,  colorless,  homogeneous  membrane,  with 
oval  nuclei  on  its  inner  surface.  In  the  fresh  condition,  the  cell  nearly 
fills  the  cavity  of  its  capsule ;  but  in  preparations  obtained  with  hard- 
ening fluids  there  is  usually  more  or  less  shrinkage  or  condensation  of 
the  cell  substance,  so  that 
it  appears  surrounded  by 
a  vacant  space,  limited  by 
the  inner  surface  of  the 
capsule  (Fig.  92).  The 
cell-process,  as  it  emerges, 
is  accompanied  by  a  tubu- 
lar prolongation  of  the 
capsule,  in  which  it  lies 
enclosed. 

Connection  between 
Nerve  Fibres  and  Nerve 
Cells. —  In  all  cases  the 
nerve  fibres  are  connected 
at  their  central  origin  with 
deposits  of  gray  substance, 
into  which  they  penetrate 
and  in  which  they  pursue 
an  intricate  course  be- 
tween its  nerve  cells.  It 
is  very  difficult  to  distin- 
guish the  final  connection 
of  the  two ;  since  in  the 
dilaceration  of  fresh  speci- 
mens, both  the  fibres  and 
the  cell-processes  are  easily  torn  off;  and  in  transparent  sections  of 
hardened  specimens,  a  nerve  fibre  seldom  follows  the  exact  plane  of  the 
section  for  any  considerable  distance.  But  by  a  combination  of  both 
methods  it  has  been  shown  that  the  nerve  fibre  is  in  many  cases  a  con- 
tinuation of  the  cell-process,  and  this  continuity  is  so  frequently  visible 
that  it  may  be  regarded  as  the  normal  mode  of  connection  between 
nerve  fibres  and  nerve  cells. 

This  connection  is  often  extremely  probable,  in  the  spinal  ganglia 
of  man  and  mammalia,  from  the  appearance  of  the  cell-process,  which 
soon  after  its  origin  resembles  so  completely  an  ordinary  axis  cylinder 
that  there  is  no  perceptible  difference  between  them.  It  is  rendered 


NERVE  CELLS,  from  spinal  and  sympathetic  ganglia  of 
man,  enclosed  in  their  capsular  sheaths.  From  hardened 
preparations.  (Key  and  Eetzius.) 


358 


THE    NERVOUS    SYSTEM. 


FIG.  93. 


certain,  according  to  the  observations  of  Key  and  Retzius,*  in  the 
cerebro-spinal  ganglia  of  the  rabbit,  where  the  cell-process  follows  for 
a  time  a  winding  course  and  becomes  covered  with  a  layer  of  myeline, 
which  may  be  rendered  perfectly  distinct  by  staining  with  perosmic 

acid  (Fig.  93).    It  thus  forms  a  complete 
nerve  fibre,  often  exhibiting  its  charac- 
teristic annular  constrictions  and  inci- 
'.   \  sions,  and  sometimes  dividing  into  two 

secondary  fibres. 

Some  cell-processes,  on  the  other  hand, 
without  acquiring  a  medullary  layer, 
join  nervous  bundles  in  the  neighbor- 
hood, and  become  to  all  appearance  non- 
medullated  nerve  fibres.  In  all  these 
instances  the  tubular  prolongation,  from 
the  capsule  of  the  nerve  cell,  is  after  a 
time  closely  applied  to  the  exterior  of 
the  nerve  fibre,  becoming  continuous 
with  the  sheath  of  Schwann. 

A  transition  of  the  cell-process  into  a 
medullated  nerve  fibre  has  been  also 
found  in  the  spinal  ganglia  of  the  frog 
and  toad,  the  layer  of  myeiine  reaching 
nearly  to  its  junction  with  the  nerve 
cell.  But  it  is  most  distinctly  marked, 
and  has  been  most  frequently  seen  in 
the  ganglia  and  trunks  of  the  trigeminus 
and  vagus  nerves  of  fishes,  particularly 
the  pike  and  lamprey.  In  these  situa- 
tions there  are  scattered  nerve  cells  of 
peculiar  form  ;  namely,  elongated  or 
ovoidal,  with  a  nerve  process  at  each 

NERVE  CELL,  with  axis  cylinder  process  ..  m,  „     ,  ,,  ,  . 

and  medullated  nerve  fibre  attached;  extremity.     They  are  thence  called  "  bi- 

stained  with  perosraic  acid.    From  Gas-  polar"    Cells.       In    the    pike,    the    lliedul- 

RetLTgUODOfthCral'1MKerandla7   layer    ^rounds  the   nerve   fibre 

quite  to  its  origin  from  the  cell  ;  and  it 

sometimes  extends  over  the  cell  itself,  which,  as  well  as  the  nerve  fibre, 
is  thus  invested  with  a  layer  of  myeline.  These  bipolar  cells,  as  well 
as  similar  ones  observed  in  the  auditory  nerve-trunk  in  fishes,  some- 
times appear  hardly  more  than  nucleated  enlargements  of  the  axis 
cylinder  ;  and  they  are  generally  situated  about  midway  between  two 
annular  constrictions.  In  the  lamprey,  the  nerve  fibres  are  non-niedul- 
lated;  but  they  are  connected  with  bipolar  cells  in  the  i^mirlion  of  the 
trigeminus  and  in  the  trunk  of  the  auditory  nerve,  in  the  same  manner 
as  above  described. 


*  Anatomic  des  Nervensystems  und  des  Bindegewebes.   Stockholm,  1876.   Zwuite 
Iliilftc,  p.  39. 


GENERAL    STRUCTURE    OF    THE    NERVOUS    SYSTEM.     359 

These  facts  show  beyond  question  the  direct  anatomical  connection, 
in  many  instances,  of  the  axis  cylinder  of  nerve  fibres  with^the  processes 
of  nerve  cells.  In  the  gray  substance  of  the  brain,  medulla  oblongata, 
and  spinal  cord,  in  man  and  mammalians,  the  multipolar  nerve  cells 
often  present  certain  processes  which  assume  the  appearance  of  axis 
cylinders,  and  which  join  the  bundles  of  fibres  running  in  the  direction 
of  nerve  roots.  It  is  presumable,  therefore,  that  they  become  after 
a  time  nerve  fibres ;  although  none  of  them,  in  these  last  named  situ- 
ations, have  been  seen  invested  with  a  medullary  layer.  According  to 
Gerlach,  on  the  other  hand,  there  is  a  tract  of  gray  substance  in  the 
spinal  cord,  throughout  its  dorsal  portion,  where  the  nerve  cells,  though 
provided  with  branching  prolongations,  do  not  present  any  process 
resembling  an  axis  cylinder ;  and  in  the  sympathetic  ganglia  of  man, 
the  dog,  and  the  cat,  Key  and  Retzius  *  have  been  able  to  follow  the 
branched  cell-processes  for  considerable  distances  among  the  neighbor- 
ing tissues  without  ever  seeing  one  of  them  converted  into  a  inedullated 
nerve  fibre.  It  is  possible  that  this  may  still  have  taken  place  beyond 
the  point  of  observation  ;  but  it  must  also  be  considered  as  doubtful 
whether  some  nerve  cells  have  not  a  different  anatomical  connection 
than  that  by  cell-processes  and  axis  cylinders. 

Physiological  Properties  of  the  Nerve  Cells. — The  nerve  cells,  and 
the  gray  substance  of  which  they  form  part,  act  as  centres,  in  which 
nervous  impressions  are  received  through  the  sensitive  fibres  from  the 
periphery,  and  from  which  a  stimulus  is  sent  out  through  the  motor 
fibres  to  the  muscles.  Every  such  collection  of  gray  substance  is 
called  a  "nervous  centre."  While  the  nerve  fibres  accordingly  are 
organs  of  transmission,  the  gray  substance  and  its  nerve  cells  are  an 
apparatus  in  which  the  nervous  influence  is  changed  from  one  form  to 
another.  The  nervous  centre  receives  the  impressions  conveyed  to  it, 
and  converts  them  into  impulses  to  be  transmitted  elsewhere.  How 
this  change  is  effected  in  the  nerve  cells  is  unknown ;  but  it  is  evidently 
essential  to  the  physiological  operation  of  the  nervous  system,  since 
neither  sensation  nor  movement  is  ever  excited,  in  the  normal  condition, 
through  the  nerve  fibres,  unless  they  are  in  communication  with  a 
nervous  centre. 

In  the  action  of  the  nervous  system,  therefore,  the  communication 
established  between  different  parts  of  the  body  is  always  circuitous. 
It  passes  through  a  nervous  centre,  in  which  the  impression  coming 
from  one  organ  is  replaced  by  a  stimulus  which  excites  the  other.  This 
is  called  the  "  reflex  action  "  of  the  nervous  system,  because  it  is  first 
sent  inward  to  the  nervous  centre  and  then  returned  or  reflected  in  the 
opposite  direction.  In  this  process,  the  intermediate  act  between  the 
inward  and  outward  passage  of  the  nervous  current  is  accomplished  in 
the  gray  substance. 


*  Anatomie  des  Nervensystems  und  des  Bindegewebes.   Stockholm,  1876.   Zweite 
Halfte,  pp.  125,  137. 


CHAPTER  II. 
NERVOUS  IRRITABILITY  AND  ITS  MODE  OF  ACTION. 

THE  property  possessed  by  nerves  of  being  called  into  excitement 
by  a  stimulus  is  termed  their  "irritability."  Such  a  property 
exists  in  other  tissues  and  organs ;  and  each  one,  when  subjected  to 
a  stimulus  adapted  to  its  character,  reacts  in  a  way  peculiar  to  itself, 
and  produces  a  definite  effect.  Thus  a  gland,  when  excited,  exhibits 
the  phenomena  of  secretion ;  a  muscle,  those  of  contraction.  The 
visible  result  of  glandular  activity  is  the  accumulation  and  discharge 
of  the  secreted  fluids ;  that  of  muscular  contraction  is  a  change  of  form 
in  the  muscle,  and  a  movement  of  the  parts  to  which  it  is  attached. 
The  irritability  of  a  nerve,  on  the  other  hand,  is  not  manifested  by  any 
perceptible  change  in  its  own  tissue,  but  by  the  phenomena  of  sensation 
or  motion  in  the  organs  to  which  it  is  distributed. 

Irritability  of  Sensitive  Fibres. 

The  irritability  of  sensitive  nerve  fibres  is  manifested  by  sensation. 
This  sensation,  however,  is  not  felt  in  the  nerve,  but  in  the  nervous 
centre  where  it  terminates.  For  if  the  communication  between  a  sen- 
sitive nerve  and  the  brain  be  cut  off,  no  stimulus  subsequently  applied 
to  its  trunk  or  branches  will  give  rise  to  a  sensation.  But  if  this  con- 
nection be  retained,  while  that  with  the  external  integument  is  cut  off, 
stimulants  applied  to  the  attached  portion  of  the  nerve  will  cause  sen- 
sations more  or  less  acute,  according  to  the  stimulus  employed.  Pinch- 
ing or  pricking  the  nerve,  variations  of  temperature,  or  the  passage  of 
an  electric  current,  will  all  bring  into  action  its  irritability,  and  thus 
produce  a  sensation. 

For  this  result,  however,  two  conditions  are  essential.  First,  the 
nerve  must  be,  as  above  mentioned,  in  communication  with  its  nervous 
centre ;  and  secondly,  the  nerve  fibres  must  retain  their  irritability. 
The  irritability  of  a  sensitive  nerve  may  be  so  deadened  by  compres- 
sion, contusion,  or  cold,  that  no  stimulus  applied  to  the  part  will 
produce  a  perceptible  effect.  In  the  observations  of  Mitchell,*  the 
application  of  extreme  cold,  in  man,  to  the  region  of  the  ulnar  nerve 
at  the  elbow,  produced,  when  the  chilling  process  had  reached  a  certain 
stage,  complete  loss  of  sensibility  in  the  parts  to  which  the  nerve  is 
distributed.  The  irritability  of  a  sensitive  nerve  may  also  be  sus- 
pended by  injuries  not  involving  its  own  fibres.  Thus  division  of 
certain  parts  in  the  brain  or  spinal  cord  may  produce  a  loss  of  sen- 

*  Injuries  of  Nerves  and  their  Consequences.     Philadelphia,  1872,  p.  59. 

360 


NERVOUS    IRRITABILITY. 


361 


sibility  in  particular  regions  of  the  body,  which  disappears  after  a 
short  time,  while  other  symptoms,  immediately  dependent  on  the 
wound,  are  persistent;*  and  according  to  L'Etievant,f  section  of  one 
sensitive  nerve  may  suspend,  for  a  time,  the  sensibility  of  neighbor- 
ing fibres  derived  from  other  nerves. 

The  irritability  of  sensitive  nerve  fibres  may  also  be  abnormally 
increased  by  vascular  congestion  or  local  injuries.  The  application 
of  cold,  or  shutting  off  the  supply  of  blood  by  the  ligature  of  arteries, 
may  produce  in  the  nerve,  before  it  reaches  the  stage  of  insensibility,  a 
condition  of  unnatural  excitement,  indicated  by  pain  in  the  parts  cor- 
responding to  its  distribution. 

During  life  the  irritability  of  sensitive  nerves  is  manifested  by  con- 
scious sensation.  After  death  it  may  be  shown  to  exist,  for  a  certain 
time,  by  reflex  actions  taking  place  in  the  spinal  cord  and  other  parts 
of  the  nervous  system. 

Irritability  of  Motor  Fibres. 

The  motor  nerves  are  especially  adapted  for  the  study  of  nervous 
irritability,  because  their  excitement  produces  a  visible  muscular  con- 
traction ;  and  this  may  take  place,  after  both  the  nerve  and  its  muscle 
have  been  separated  from  the  body.  But  to  produce  this  result,  as  in 
the  case  of  the  sensitive  nerves,  two  conditions  are  requisite,  namely ; 
first,  the  nerve  fibres  must  preserve  their  irritability ;  and  secondly, 
the  muscle  must  be  capable  of  responding  to  the  nervous  stimulus. 
These  two  conditions  may  therefore  be  studied  in  con- 
nection with  each  other. 

Muscular  Irritability. — This  is  best  shown  in  the 
cold-blooded  animals,  in  which  it  continues  longer  than 
in  birds  or  mammalians.  If  a  frog's  leg  be  separated 
from  the  body,  the  skin  removed,  and  the  poles  of  a 
galvano-electric  apparatus  (Fig.  94,  a,  b)  applied  to  the 
denuded  muscles,  a  contraction  takes  place  each  time 
the  circuit  is  completed.  In  this  case,  the  electric 
stimulus  acts  directly  on  the  muscles,  and  thus  calls 
out  their  contractility.  A  single  muscular  fibre,  placed 
under  the  microscope,  may  sometimes  be  seen  to  con- 
tract for  a  certain  time  after  its  separation  from  the 
neighboring  parts.  The  muscles  may  also  be  excited 
by  pinching,  pricking,  the  contact  of  hot  or  cold  bodies, 

f,  T.VL-  *       •  i      11     i.  T  i    ,.  FROG'S  LEG,  with 

or  the  application  of  acid,  alkaline,  or  saline  solutions.  the  poies  Of  &  gai- 
But  the  most  efficient  and  manageable  stimulus  is  the  vanic  battery  ap- 
electric  discharge. 

Nervous  Irritability. — To  exhibit  the  irritability  of 
motor  nerve  fibres,  a  frog's  leg  is  prepared,  as  in  the  preceding  experi- 
ment, except  that  a  portion  of  the  sciatic  nerve  is  retained  in  connection 

*  Veyssi&re  Kecherches  sur  1'Hemianaesthesie.     Paris,  1874,  p.  78. 
f  Trait6  des  Sections  Nerveuses.     Paris,  1873,  pp.  171,  192. 


FIG.  94. 


362 


THE    NERVOUS    SYSTEM. 


FIG.  95. 


FROG'S  LEG  with 
the  sciatic  nerve 


with  the  amputated  limb  (Fig.  95).  If  the  electrodes  be  now  applied 
to  the  exposed  nerve,  and  a  current  allowed  to  pass  between  them, 
at  the  moment  of  its  passage  a  contraction  takes  place  in  the  muscles 
below.  In  this  case  the  electric  current  acts  on  the  nerve 
alone  :  and  the  nerve  excites  the  muscles  by  its  own 
special  agency.  A  muscular  contraction,  therefore,  under 
the  influence  of  a  stimulus  applied  to  the  nerve,  demon- 
strates the  nervous  irritability,  and  may  be  used  as  a 
convenient  measure  of  its  intensity. 

The  irritability  of  a  motor  nerve  continues  after 
death.  This  follows  from  the  foregoing  experiment. 
The  irritability  of  the  nerve,  like  that  of  the  muscles, 
depends  upon  its  anatomical  structure  and  constitution  ; 
and  so  long  as  these  continue,  the  nerve  retains  its 
physiological  properties.  For  the  same  reason,  nervous 
irritability  lasts  longer  after  death  in  the  cold-blooded 
than  in  tlie  warm-blooded  animals.  Various  artificial  irri- 
tants may  be  employed  to  call  it  into  activity.  Pinching 
or  pricking  the  exposed  nerve  with  steel  instruments,  the 
application  of  caustic  liquids,  and  the  galvanic  current, 
all  have  this  effect.  Galvanism,  however,  is  the  best 
means  for  this  purpose,  as  it  is  more  delicate  in  its  opera- 
t^on  tnan  ^e  otners>  and  wiN  succeed  for  a  longer  time. 
Nervous  irritability,  like  that  of  the  muscles,  is  ex- 
hausted  by  repeated  excitement.  If  an  amputated  frog's 
battery  (a,  leg,  with  the  sciatic  nerve  attached,  be  kept  in  a  cool 
Placc»  protected  from  desiccation,  the  nerve  will  remain 
irritable  for  many  hours  ;  but  if  excited  by  repeated  stim- 
ulus, it  soon  begins  to  react  with  diminished  energy,  and  at  last  ceases 
to  exhibit  any  further  irritability.  If  now  allowed  to  remain  at  rest,  its 
irritability  will  partially  return  ;  and  muscular  contraction  will  again 
ensue  on  the  application  of  a  stimulus  to  the  nerve.  Exhausted  a  second 
time,  and  a  second  time  allowed  to  repose,  the  nerve  will  again  recover 
itself  ;  and  this  may  be  repeated  several  times  in  succession.  At  each 
repetition,  however,  the  recovery  of  nervous  irritability  is  less  complete, 
until  finally  it  can  no  longer  be  recalled. 

Various  circumstances  tend  to  diminish  or  suspend  the  irritability 
of  motor  nerve  fibres.  As  in  the  case  of  the  sensitive  fibres,  compres- 
sion, cold,  or  other  similar  agencies  will  depress  the  power  of  the 
muscular  nerves,  so  that  they  can  no  longer  excite  contraction  when 
subjected  to  the  galvanic  current.  Severe  and  sudden  mechanical 
injuries  often  have  the  same  effect  ;  as  where  general  relaxation,  or 
diminished  power  of  voluntary  motion,  is  produced,  in  man,  by  exten- 
sive contusion  or  laceration  of  the  limbs.  Such  an  injury  produces 
a  disturbance  or  shock,  which  affects  the  entire  nervous  system, 
and  suspends  its  irritability;  diminishing  for  the  time  both  mus- 
cular power  and  sensibility.  It  is  only  after  nervous  irritability 


*  ' 


NERVOUS    IRRITABILITY.  363 

has  been  restored  by  repose,  that  voluntary  motion  and  sensation  are 
reestablished. 

Different  Action  of  the  Direct  and  Inverse  Currents. — A  galvanic 
current  which  traverses  the  nerve  in  the  direction  of  its  motor  fibres, 
namely,  from  the  centre  toward  the  periphery,  as  from  a  to  b  (Fig.  95), 
is  called  a  direct  current.  If  made  to  pass  in  the  contrary  direction, 
from  b  to  a,  it  is  called  an  inverse  current.  When  the  nerve  is  exceed- 
ingly irritable,  or  with  a  galvanic  current  of  considerable  intensity, 
muscular  contraction  takes  place  at  both  the  commencement  and 
termination  of  the  current,  whether  direct  or  inverse.  But  when  the 
activity  of  the  nerve  has  become  somewhat  diminished,  or  when  the 
current  employed  is  of  feeble  intensity,  contraction  takes  place  only  at 
the  commencement  of  the  direct  and  at  the  termination  of  the  inverse 
current.  If  both  hind  legs  of  a  frog  be  prepared  in  such  a  way  that 
they  remain  connected  with  each  other  by  the  sciatic  nerves  and  a 
portion  of  the  spinal  column,  when  the  positive  pole  of  a  battery  is 
applied  to  the  right  foot  and  the  negative  pole  to  the  left,  the  current 
passing  through  the  sciatic  nerves  will  be  an  inverse  current  for  the 
right  nerve,  and  a  direct  current  for  the  left  nerve.  At  the  moment 
of  completing  the  circuit,  a  contraction  will  take  place  in  the  left 
leg,  but  not  in  the  right ;  and  when  the  current  is  broken,  the  right 
leg  contracts,  while  the  left  remains  at  rest.  If  the  position  of  the  poles 
be  reversed,  the  effects  of  the  current  will  be  changed  in  a  corresponding 
manner. 

After  a  nerve  has  become  exhausted  by  the  direct  current,  it  is  still 
sensitive  to  the  inverse ;  and  after  exhaustion  by  the  inverse,  it  is  still 
sensitive  to  the  direct.  It  was  even  found  by  Matteucci  that  when  a 
nerve  has  been  temporarily  exhausted  by  the  direct  current,  the  return 
of  its  irritability  is  hastened  by  the  subsequent  passage  of  the  inverse 
current ;  so  that  it  will  become  again  sensitive  to  the  direct  current 
sooner  than  if  allowed  to  remain  at  rest.  Nothing,  accordingly,  is  so 
exciting  to  a  nerve  as  the  passage  of  direct  and  inverse  currents,  follow- 
ing each  other  in  quick  succession.  Such  a  form  of  galvanism  is  that 
afforded  by  the  Faradic  apparatus,  in  which  rapidly  alternating  currents 
of  induced  electricity  traverse  the  circuit  in  opposite  directions. 

The  irritability  of  motor  nerves  is  distinct  from  that  of  the  muscles. 
This  is  shown  by  the  fact  that  the  two  properties  may  be  suspended 
independently  of  each  other.  In  the  experiment  above  described,  the 
irritability  of  the  nerve  is  manifested  only  through  that  of  the  muscle, 
and  that  of  the  muscle  is  called  into  action  only  through  that  of  the 
nerve.  But  under  the  influence  of  woorara,  the  action  of  the  motor 
nerve,  as  shown  by  Bernard,*  may  be  suspended  without  affecting 
the  irritability  of  the  muscles.  In  a  frog,  poisoned  by  this  substance, 
the  poles  of  a  galvanic  battery  applied  to  the  sciatic  nerve  will  produce 
no  effect.  But  if  the  galvanic  current  be  passed  directly  through  the 


Le9ons  sur  la  Physiologie  du  Systeme  Nerveux.     Paris,  1858,  tome  i.,  p.  199. 


364  THE    NERVOUS    SYSTEM. 

muscles  of  the  leg-,  contraction  takes  place.  The  muscular  irrita- 
bility survives  that  of  the  nerves,  and  is  therefore  essentially  dis- 
tinct from  ii. 

The  independence  of  muscular  and  nervous  irritability  is  also  indicated 
by  the  effects  following  degeneration  of  divided  nerve  fibres  (page  353). 
When  a  motor  nerve  is  divided,  the  separated  portion  after  a  few  days 
loses  its  irritability,  so  that  no  stimulus  applied  to  it  will  excite  con- 
traction in  the  corresponding  muscles.  But  if  a  galvanic  current  be 
applied  to  the  muscles  themselves,  they  contract.  Longet*  has  demon- 
strated this  fact  upon  the  dog,  from  five  days  to  twelve  weeks  after 
section  of  the  facial  nerve ;  and  a  similar  result  has  been  found  by 
Yulpianf  in  the  rabbit  thirty  days  after  section  of  the  same  nerve. 
The  contraction  in  these  cases  cannot  be  attributed  to  the  irritability 
of  small  nerve  branches  included  in  the  muscular  tissue,  since  the 
degeneration  of  a  divided  nerve  takes  place  throughout  its  peripheral 
portion  ;  and  according  to  Ranvier|,  from  forty-eight  hours  to  five  days 
after  division  of  the  sciatic  nerve  in  the  rabbit,  the  terminal  nerve  fibres 
in  the  muscles  of  the  leg  are  as  fully  degenerated  as  those  in  the 
trunk  of  the  nerve  near  its  point  of  section.  The  irritability  of  the 
muscles  must  therefore  be  regarded  as  a  property  belonging  to  their 
own  tissue,  but  capable  of  responding  to  a  stimulus  communicated  by 
the  nerves. 

Identity  of  Action  in  Sensitive  and  Motor  Fibres. 

The  results  of  nervous  action  are  different  in  the  two  kinds  of 
nerve  fibres.  The  stimulation  of  sensitive  fibres  produces  a  sensation, 
or  sensitive  impression  in  the  nervous  centre ;  that  of  motor  fibres 
causes  muscular  contraction  at  the  periphery.  Moreover,  if  a  sensitive 
nerve  be  divided,  stimulus  applied  to  its  central  extremity  still  excites 
a  sensation,  while  the  same  stimulus,  applied  to  its  peripheral  portion, 
produces  no  apparent  result.  On  the  other  hand,  if  a  motor  nerve 
be  divided,  irritation  of  its  attached  extremity,  which  is  still  in  con- 
nection with  the  nervous  centre,  has  no  effect;  but  irritation  of  its 
peripheral  portion  causes  muscular  contraction  as  before.  In  other 
words,  the  nervous  force,  in  a  sensitive  nerve,  appears  to  move  in  a 
centripetal  direction,  that  is  from  without  inward;  and  in  a  motor  nerve, 
in  a  centrifugal  direction,  or  from  within  outward.  The  excitement  of 
a  sensitive  nerve,  furthermore,  never  produces  any  other  immediate 
effect  than  a  sensation ;  that  of  a  motor  nerve  only  gives  rise  to  the 
phenomena  of  movement. 

The  above  facts  suggest  the  idea  that  the  two  kinds  of  nerve  fibres 
may  be  distinct  in  their  properties  and  modes  of  action ;  that  the  sensi- 
tive fibres  may  be  capable  of  acting  only  in  a  centripetal  direction  and 
of  exciting  sensibility ;  and  that  the  motor  fibres  can  only  act  from 

*  TraitS  de  Physiologic.     Paris,  1850,  tome  ii.,  p.  51. 

f  Lefons  sur  la  Physiologic  due  SystSme  Nerveux.     Paris,  1866,  p.  245. 

t  Lefons  sur  1'Histologie  du  Systeme  Nerveux.     Paris,  1878,  tome  ii.,  p.  349. 


NERVOUS    IRRITABILITY.  365 

within  outward,  transmitting  a  special  nerve  force,  adapted  to  excite 
muscular  contraction. 

It  is  evident,  however,  that  these  reasons  do  not  indicate  a  real  differ- 
ence in  the  activity  of  the  nerve  fibres,  but  only  in  the  sensible  results 
of  its  operation.  In  neither  case  is  there  any  perceptible  effect  produced 
in  the  nerve,  but  only  in  the  organ  with  which  it  is  connected.  When 
a  sensitive  nerve  is  excited,  the  sensation  is  perceived  in  the  nervous 
centre ;  when  a  motor  nerve  is  called  into  activity,  contraction  takes 
place  in  the  muscle.  It  is  possible  that  the  condition  of  the  nerve 
under  excitement  may  be  the  same  in  both  cases,  and  that  the  differ- 
ence in  effect  may  be  due  only  to  the  organ  in  which  it  terminates ; 
just  as  the  conducting  wire  of  a  galvanic  battery  may  be  made  to  ring 
a  bell  or  move  an  index,  according  to  the  mechanism  with  which  it  is 
connected.  There  are  some  facts  which  can  hardly  bear  any  other 
interpretation  than  this,  and  which  lead  to  the  conclusion  that  the 
physiological  action  in  the  two  kinds  of  nerve  fibres  is  not  essentially 
different. 

1.  The  stimulus  applied  to  a  nerve,  either  sensitive  or  motor,  pro- 
duces the  same  effect  throughout  its  entire  length. 

Impressions  made  upon  the  integument,  which  give  rise  to  sensation, 
are  transmitted  by  the  sensitive  nerve  through  its  whole  course  to  the 
nervous  centre ;  and  the  sensation  thus  produced  is  referred,  not  to  the 
brain  or  to  any  part  of  the  nerve  trunk,  but  to  its  point  of  distribution 
in  the  integument.  An  irritation  applied  to  the  same  nerve  in  the  mid- 
dle of  its  course  produces  a  sensation  which  still  seems  to  come  from 
the  integument.  After  the  amputation  of  a  limb  in  man,  if  the  severed 
extremity  of  a  nerve  be  compressed  or  irritated  in  the  cicatrix,  the 
sensations  excited  are  referred  to  the  amputated  limb ;  and  patients 
often  assert  that  they  can  feel  the  separated  parts  as  distinctly  as 
before.  The  impression  conveyed  through  the  remaining  portion  of 
the  nerve  is  the  same  as  if  the  whole  of  it  were  still  in  existence. 

The  motor  nerves  act  in  a  similar  way.  A  voluntary  stimulus  orig- 
inating in  the  brain  passes  through  the  entire  length  of  a  motor  nerve 
to  reach  the  muscles  and  excite  their  contraction.  If  the  nerve  be 
divided  at  any  intermediate  point,  and  a  galvanic  stimulus  applied  to 
the  peripheral  portion,  contraction  follows  in  the  muscles  as  before.  In 
each  case,  the  physiological  effect  is  produced  at  the  extremity  of  the 
nerve  fibres ;  and  is  apparently  of  the  same  character,  from  whatever 
distance  it  has  been  transmitted. 

It  appears  accordingly  that  the  nerve  fibre,  whether  sensitive  or 
motor,  when  excited,  is  thrown  into  a  condition  of  activity  throughout 
its  length;  the  nerve  assuming  a  state  of  " polarity,"  analogous  to 
that  of  a  magnetized  bar,  in  which  the  visible  phenomena  of  attrac- 
tion or  repulsion  are  manifested  only  at  its  extremities,  although  the 
intermediate  portions  of  the  bar  participate  in  its  molecular  action. 
When  the  exciting  stimulus,  in  a  sensitive  nerve,  is  applied  at  the 
peripheral  extremity,  it  must  necessarily  be  transmitted  from  without 


366  THE    NERVOUS    SYSTEM. 

inward ;  and  when  it  commences  at  the  inner  extremity,  as  in  a  motor 
nerve,  it  must  move  from  within  outward.  But  under  other  conditions 
it  may  be  capable  of  moving  in  either  direction.  The  following  experi- 
ment shows  that  this  is  possible,  so  far  as  regards  the  sensitive  nerves. 

2.  Sensitive  impressions  may  pass,  in  the  fibres  of  a  sensitive  nerve, 
either  from  without  inward  or  from  within  outward. 

This  of  course  never  takes  place  in  the  normal  condition  ;  but  its  pos- 
sibility has  been  demonstrated,  in  the  experiments  of  Paul  Bert,*  by 
dividing  a  sensitive  nerve  and  then  reversing  its  position,  so  that  its 
peripheral  extremity  is  in  connection  with  the  nerve  centres.  The 
end  of  the  tail,  in  a  young  rat,  was  deprived  of  integument  for  a 
length  of  five  centimetres,  and  the  denuded  portion  inserted  beneath 
the  skin  of  the  back  of  the  same  animal.  At  the  end  of  eight  days, 
when  the  ingrafted  portion  had  become  adherent  to  the  subcutaneous 
tissues,  and  had  contracted  sufficient  vascular  connection  for  its  support, 
the  tail  was  amputated  at  its  base,  and  thenceforward  remained  attached 
to  the  body  of  the  animal  only  by  what  was  previously  its  peripheral 
extremity.  In  three  months  sensibility  again  began  to  be  manifest  e<  I 
in  the  end  of  the  tail,  thus  reversed;  and  in  six  months  it  was 
reestablished  to  an  unmistakable  degree.  The  nerves  of  the  tail, 
which  before  the  operation  transmitted  sensitive  impressions  from  its 
point  toward  its  base,  afterward  transmitted  the  same  impressions  from 
its  base  toward  its  point.  In  this  instance  the  nerve  fibres  which  thus 
acted  in  a  reverse  direction  were  fibres  of  new  formation,  like  those 
which  generally  replace  the  degenerated  fibres  of  divided  nerves  (page 
355) ;  but  there  is  no  evidence  that  such  regenerated  fibres  are  in  any 
way  different  from  those  originally  existing  in  the  same  parts. 

Although  the  nerve  fibres  therefore  may  excite  two  different  forms 
of  action,  their  own  condition  may  be  the  same  for  both.  If  they  com- 
municate their  stimulus  to  a  perceptive  nervous  centre  the  effect  is  a 
sensation  ;  if  to  a  muscle,  it  is  contraction.  These  acts  cannot  be  inter- 
changed with  each  other,  because  the  muscle  is  not  sensitive  and  the 
nervous  centre  is  not  contractile ;  but  they  are  both  indirect  effects  of 
the  nervous  influence,  and  do  not  necessarily  indicate  any  difference  in 
its  nature. 

Rapidity  of  Transmission  of  the  Nerve  Force. 

It  is  a  matter  of  conscious  experience  that  the  operations  of  the 
nervous  system  require  a  certain  time  for  their  accomplishment.  The 
action  both  of  the  senses  and  of  the  will,  though  exceedingly  rapid, 
is  not  instantaneous.  Between  the  mental  decision  to  perform  a 
movement  and  its  actual  execution,  there  is  a  short  but  real  interval  of 
time,  during  which  the  nervous  mechanism  is  called  into  play.  A  cer- 
tain period  also  intervenes  between  the  contact  of  a  foreign  body  with 
the  skin,  and  our  perception  of  its  existence  and  qualities.  There  is 
even  more  or  l«-ss  difference  between  individuals  in  the  time  required 

*  La  Vitality  propre  des  Tissues  aniraaux.    Paris,  1866,  p.  12. 


NBBVOUfl    IRRITABILITY.  367 

for  nervous  action ;  the  quickness  of  the  senses  and  the  promptitude 
of  the  will  frequently  varying  to  a  perceptible  degree.  In  the  case  of 
a  voluntary  movement,  the  period  consumed  is  occupied  by  three  dif- 
ferent processes,  namely  :  1.  The  act  of  volition,  in  the  brain ;  2.  The 
transmission  of  the  motor  impulse,  through  the  spinal  cord  and  nerves, 
to  its  destination ;  and  3.  The  excitement  of  the  muscle  to  contrac- 
tion. In  the  case  of  a  sensation,  there  are  three  analogous  successive 
acts,  namely:  1.  Reception  of  the  impression  by  the  sensitive  mem- 
brane; 2.  Transmission  of  the  stimulus  through  the  nerve  toward  the 
brain  ;  and  3.  Its  perception  in  the  brain  as  a  conscious  sensation.  It 
is  important  to  determine  the  rapidity  of  nervous  communication  in  each 
direction. 

Methods  of  Determining  the  Rate  of  Transmission  of  the  Nerve  Force. 
— The  rate  of  transmission  of  the  nerve  force,  first  measured  by 
Helmholtz,*  has  since  been  investigated  by  different  observers  with 
essentially  similar  results.  The  principle  adopted  is  in  all  cases  the 
same.  Muscular  contraction  is  excited  by  a  stimulus  which  passes 
through  two  nerves  of  different  length,  or  through  two  different  lengths 
of  the  same  nerve ;  the  delay  in  contraction,  when  the  stimulus  passes 
through  the  longer  of  these  routes,  gives  the  time  required  to  traverse 
the  additional  distance. 

These  experiments  were  first  performed  on  separated  nerves  and 
muscles  of  the  cold-blooded  animals.  The  gastrocnemius  muscle  of  a 
frog  is  prepared,  with  a  portion  of  the  sciatic  nerve  attached.  A  gal- 
vanic battery  with  an  induction  apparatus  is  also  provided,  so  that  the 
closure  of  the  battery  circuit  will  produce  an  instantaneous  current  in 
the  induction  coil.  This  induced  current  is  first  applied  to  the  muscle, 
and  the  time  noted  which  intervenes  between  the  closure  of  the  circuit 
and  the  muscular  contraction.  This  represents  the  period  required  for 
the  excitement  of  the  muscular  fibres,  and  was  found  by  Helmholtz  to 
be  about  yj^  of  a  second.  If  the  stimulus  be  now  applied  to  the  nerve 
near  its  termination  in  the  muscle,  the  interval  is  not  perceptibly 
changed.  But  if  it  be  applied  at  a  point  one,  two,  or  three  centimetres 
distant,  a  retardation  is  manifested  in  the  muscular  contraction ;  and 
this  retardation  becomes  greater  as  the  distance  between  the  muscle 
and  the  point  of  stimulation  is  increased. 

The  intervals  of  time  in  these  experiments  have  been  measured  by 
various  contrivances,  the  most  successful  of  which  is  an  automatic 
registering  apparatus  like  that  of  Marey  (page  284).  Upon  the  surface 
of  the  revolving  cylinder  the  extremity  of  a  tuning-fork,  vibrating  500 
times  per  second,  traces  an  undulating  line  (Fig.  96,  a)  which  records 
the  time  occupied  in  moving  from  one  point  to  another.  A  straight 
horizontal  line  (b)  is  also  traced  upon  the  same  surface  by  the  extremity 
of  a  slender  lever,  the  other  end  of  which  forms  part  of  the  galvanic 
circuit.  The  closure  of  the  circuit  is  accomplished  by  a  movement 

*  Comptes  Eendus  de  1' Academic  des  Sciences.    Paris,  1851,  tome  xxxiii.,  p.  262. 


368  THE    NERVOUS    SYSTEM. 

which  pushes  aside  the  lever,  causing  in  the  traced  line  a  momentary 
deviation  (d),  which  thus  registers  the  instant  of  the  stimulation  of 
the  nerve.  The  muscle  used  for  experiment  is  attached  by  its  tendon 

FIG.  96. 


DIAGRAM  OF  THE  REGISTERING  APPARATUS,  according  to  the  plan  of  Marey.  a.  Undulating  line 
traced  by  the  tuning-fork,  which  marks  the  time  consumed  by  the  card  in  moving  from  one  point  to 
another.  6.  Line  traced  by  the  first  lever,  forming  part  of  the  galvanic  circuit,  c.  Line  traced  by 
the  second  lever,  which  is  moved  by  the  contraction  of  the  muscle,  d.  Deviation  of  the  line  b, 
indicating  the  closure  of  the  galvanic  circuit  and  the  stimulation  of  the  nerve,  e.  Deviation  of 
the  line  c,  indicating  the  muscular  contraction. 

to  a  second  lever  in  such  a  way  that  any  muscular  contraction  will 
draw  aside  its  free  extremity.  This  lever,  while  at  rest,  traces  a  second 
horizontal  line  (c)  below  the  first ;  and  when  the  muscle  contracts,  the 
line  is  deviated,  as  at  (e),  by  the  movement  of  the  lever. 

There  are  thus  left  upon  the  registering  surface  two  deviations,  d  and 
e,  one  of  which  records  the  stimulation  of  the  nerve,  the  other  the 
muscular  contraction ;  and  between  the  two  there  is  a  certain  interval. 
The  number  of  undulations  in  the  trace  a,  corresponding  to  this  interval, 
indicates  the  time  which  has  elapsed  between  the  stimulation  of  the 
nerve  and  the  muscular  contraction.  In  the  example  shown  at  Fig.  96, 
as  the  interval  between  the  deviations  includes  13  simple  vibrations,  of 
which  500  would  represent  one  second,  the  time  occupied  is  0.026  of  a! 
second.  By  this  means,  intervals  of  very  short  duration  may  be  accu- 
rately registered. 

Subsequently  investigations  of  a  similar  kind  were  applied  to  the 
man  during  life.  In  the  experiments  of  Baxt,*  this  was  done  by 
applying  electrodes  to  the  skin  over  the  median  nerve,  at  varying 
distances  from  its  muscular  distribution.  The  nerve  was  thus  stimu- 
lated at  the  Vrist,  at  the  elbow,  and  at  the  upper  arm  ;  the  effect  being 
marked  by  the  swelling  of  the  muscles  at  the  ball  of  the  thumb.  The 
time  intervening  between  the  application  of  the  electrodes  and  the 
muscular  contraction  was  greater  with  the  stimulus  applied  at  the  upper 
arm,  than  at  the  wrist ;  the  difference  being  evidently  the  time  required 
to  transmit  of  the  nervous  impulse  from  the  first  point  to  the  second. 
The  rate  of  transmission,  as  ascertained  by  these  experiments,  varied 
according  to  the  conditions  of  cold  or  warmth;  being  less  rapid  ;it  a 
low  than  at  a  high  temperature. 


* Monatsbericht  der  koniglichen  Preussischen  Akadenrie,  1867  and 


NERVOUS    IRRITABILITY.  369 

Finally,  the  rate  of  transmission  of  the  nerve-force,  in  man,  for  both 
voluntary  motion  and  conscious  sensation,  has  been  investigated  by 
Burckhardt,*  with  a  registering  apparatus  in  which  the  beginning  and 
end  of  the  nervous  transmission  were  marked,  as  above,  by  the  devia- 
tions of  a  traced  line. 

Rate  of  Transmission  in  the  Motor  Nerves. — The  transmission  of 
the  voluntary  impulse  was  measured  by  Burckhardt  as  follows :  The 
apparatus  being  attached  to  the  person  serving  for  experiment,  the 
signal  for  voluntary  motion  was  given  by  a  bell  connected  with  the 
battery.  Thus  the  entire  interval  registered  was  that  between  the 
sound  of  the  bell  and  the  muscular  contraction.  A  part  of  this  time 
was  consumed  in  hearing  the  sound  and  producing  the  volitional 
impulse.  Another  part  was  taken  up  by  the  process  of  muscular  con- 
traction ;  and  only  the  remainder  was  occupied  by  nervous  transmission. 
But  when,  in  different  observations,  the  same  signal  was  used  for 
the  contraction  of  muscles  supplied  by  different  lengths  of  nerve,  the 
processes  taking  place  in  the  brain  and  in  the  muscle  would  be  alike 
in  all ;  and  any  difference  in  the  time  observed  must  be  due  to  the 
different  lengths  of  nerve  traversed  by  the  motor  impulse.  The 
muscles  employed  for  this  purpose  were,  in  the  lower  limb,  the 
extensor  digitorum  communis  brevis,  tibialis  anticus,  and  semimem- 
branosus,  supplied  by  branches  of  the  sciatic  nerve,  and  the  quadriceps 
extensor  cruris,  supplied  by  the  anterior  crural  nerve ;  in  the  upper 
limb,  the  interosseus  externus  primus,  extensor  digitorum  communis, 
flexor  digitorum  and  deltoid,  all  supplied  by  branches  of  the  brachial 
plexus.  The  mean  result  of  these  observations,  on  eight  healthy 
persons,  gave  a  velocity  of  transmission,  in  the  nerves  of  the  upper 
and  lower  limbs,  of  a  little  over  27  metres  per  second.  The  minimum 
velocity  was  20  metres,  and  the  maximum  36  metres ;  but  of  all  the 
observations,  thirty  in  number,  twenty-three,  or  nearly  four-fifths,  gave 
results  between  26  and  28  metres. 

In  one  instance  the  rate  of  movement  for  the  voluntary  impulse  and 
for  that  excited  by  galvanism  was  tested  in  the  same  nerve,  with  but 
little  difference  in  the  results. 

According  to  Burckhardt,  furthermore,  the  rate  of  transmission  does 
not  vary  essentially  for  weak  or  strong  motor  impulses ;  that  for  a  mus- 
cular contraction  of  moderate  force  passing  as  rapidly  through  the 
nerve  as  that  for  contractions  of  greater  power. 

Rate  of  Transmission  in  the  Sensitive  Nerves. — The  rate  of  trans- 
mission for  impressions  of  conscious  sensibility  is  determined  by  a  simi- 
lar method.  A  tactile  impression  is  made  upon  the  skin  at  varying 
distances  from  the  nervous  centre — as,  for  instance,  upon  the  foot,  the 
thigh,  and  the  loins ;  the  instant  at  which  the  sensation  is  perceived 
being  indicated  by  a  movement  of  the  finger.  As  the  time  required 
for  conscious  perception  in  the  brain  and  for  voluntary  movement  of 


*  Die  Fhysiologische  Diagnostik  der  Nervenkranheiten.     Leipzig,  1875,  p.  32. 

Y 


370  THE    NERVOUS    SYSTEM. 

the  finger  is  the  same  in  all  cases,  the  difference  between  successive 
observations  is  due  to  the  different  lengths  of  nerve  transmitting  the 
impression. 

In  the  experiments  of  Burckhardt,  made  on  thirteen  different  per- 
sons, the  mean  rate  of  transmission  for  sensitive  impressions  through 
the  nerves  was  a  little  less  than  4T  metres  per  second ;  that  is,  more 
than  one  and  a  half  times  as  rapid  as  that  for  voluntary  motion. 
The  variations  were  from  a  minimum  of  20  to  a  maximum  of  73 
metres;  but  in  nearly  three-fourths  of  all  the  observations,  tin-  results 
were  confined  within  the  limits  of  40  and  56  metres.  The  rapidity 
of  transmission  varied  but  little  with  the  intensity  of  the  impres- 
sion ;  the  difference,  on  the  average,  being  but  little  over  one  per 
cent.  The  average  rate  for  different  kinds  of  nervous  action  is 
accordingly  as  follows : 

RATE  OF  TRANSMISSION  THROUGH  THE  NERVES. 
For  voluntary  motion        .        .         .         .27  metres  per  second. 
For  sensation 47       "       "        " 

Rate  of  Transmission  in  the  Spinal  Cord. — The  investigations  of 
Burckhardt  first  indicated  a  difference  between  the  rate  of  transmission 
in  the  spinal  cord  and  that  in  the  nerves.  This  rate  was  determined 
for  the  spinal  cord  by  comparing  the  passage  of  a  voluntary  impulse 
through  two  nerves,  like  the  sciatic  and  the  ulnar,  which  emerge 
from  the  spinal  cord  at  different  points.  In  this  case  the  impulse,  after 
leaving  the  brain,  traverses  different  lengths  of  the  spinal  cord ;  and  as 
its  rate  of  movement  in  the  peripheral  nerves  is  known,  the  difference 
in  time  of  its  entire  passage  gives  its  rate  of  movement  in  the  spinal 
cord.  Thus  a  motor  impulse,  which  calls  into  action  the  interosseous 
muscles  of  the  hand,  passes  through  the  cervical  portion  of  the  spinal 
cord,  the  lower  cervical  nerves,  the  brachial  plexus,  and  the  ulnar 
nerve.  An  impulse  which  excites  contraction  in  the  quadriceps  exten- 
sor cruris  passes  through  the  cervical  and  dorsal  portions  of  the  cord, 
and  thence  through  the  lumbar  plexus  and  the  anterior  crural  nerve  to 
the  thigh.  Consequently  its  transit  through  the  spinal  cord  is  about 
three  times  as  long  ui  the  second  case  as  in  the  first ;  and  the  amount 
of  its  retardation  must  correspond  with  this  difference. 

By  this  means  it  was  found  that  the  transmission  of  voluntary  motor 
impulses  in  the  spinal  cord  is  considerably  slower  than  in  the  nor 
Its  average  rapidity  was  a  little  over  10  metres  per  second;  the  mini- 
mum being  8,  the  maximum  14  metres.  Thus  the  difference  in  rnpid- 
ity  of  transmission  through  the  nerves  and  the  spinal  cord  is  very 
manifest. 

A  comparison  of  the  opposite  sides  of  the  body  <rave  a  difference 
in  the  rate  of  transmission,  for  the  ri^-Iit  and  left  halves  of  the  spinal 
cord,  of  from  one  to  three  metres  per  second,  always  in  favor  of  the 
left  side. 

The  transmission  of  sensitive  impression*  through  the  spinal  cord, 


NERVOUS    IRRITABILITY.  371 

on  the  other  hand,  was  found  to  be  nearly  as  rapid  as  through  the 
nerves,  the  average  rate  being  a  little  over  42  metres  per  second. 
There  was  a  remarkable  difference,  however,  in  this  respect,  between 
tactile  impressions  and  those  of  a  painful  character.  The  latter  are 
transmitted  at  a  much  slower  rate,  amounting  on  the  average  to  not 
more  than  13  metres  per  second.  Thus  the  transmission  of  motor 
impulses  and  of  tactile  and  painful  impressions  respectively,  through 
the  spinal  cord,  is  as  follows  : 

RATE  OF  TRANSMISSION  THROUGH  THE  SPINAL  COED. 
For  tactile  impressions      .        .         .        .42  metres  per  second. 

u    painful 13       u        "        " 

"    motor  impulses 10      u        "        " 

According  to  these  results  the  passage  of  a  motor  impulse,  from  the 
brain  to  the  muscles  of  the  foot,  would  occupy  0.088  of  a  second ;  of 
which  about  one-half  would  be  required  for  transmission  through  the 
spinal  cord,  and  one-half  for  transmission  through  the  nerves. 

Rapidity  of  Nervous  Action  in  the  Brain. — In  the  above  experi- 
ments, an  essential  part  of  the  nervous  operation  consists  in  hearing 
the  signal  for  a  voluntary  movement  and  in  the  volition  which  gen- 
erates the  motor  impulse.  The  time  thus  consumed  is  ascertained  by 
deducting,  from  the  whole  period  between  a  given  signal  and  a  vol- 
untary movement,  first,  the  time  requisite  for  muscular  contraction, 
namely,  0.01";  and,  secondly,  that  occupied  in  transmitting  the  impulse 
through  the  spinal  cord  and  nerves.  Thus  if  the  entire  period  be 
0.220",  and  the  time  required  for  transmission  through  the  spinal 
cord  and  nerves  be  0.088",  there  remains  0.132",  which  is  occupied  in 
muscular  contraction  and  in  the  acts  of  sensation  and  volition.  Burck- 
hardt's  experiments,  like  those  of  Helmholtz,  fix  the  time  required 
for  local  stimulation  of  the  muscle  at  0.01";  and  he  estimates  that 
about  an  equal  interval  is  necessary  for  the  mechanism  of  hearing. 
The  whole  process,  therefore,  of  executing  a  voluntary  movement  in 
the  foot,  at  the  signal  of  a  bell,  would  be  divided  as  follows : 

TIME  OCCUPIED  IN  EXECUTING  A  VOLUNTARY  MOVEMENT  AT  A  GIVEN  SIGNAL. 
Mechanism  of  hearing      .......     0.010" 

Acts  of  perception  and  volition  in  the  brain     .         .        .     0.112" 
Transmission  through  the  spinal  cord        ....     0.044" 

Transmission  through  the  sciatic  nerve  • .         .         .         .     0.044" 

Mechanism  of  muscular  contraction          ....     0.010" 

,   0.220" 

It  appears  that  the  action  in  the  brain,  representing  the  operation 
of  the  gray  substance  of  the  nervous  centres,  requires  a  consider- 
ably longer  time  than  the  transmission  of  impulses  through  the  nerve 
fibres. 

Personal  Error  and  Personal  Equation. — The  different  rapidity  of 
nervous  action,  in  different  individuals,  causes  a  variation  in  the  prompti- 


372  THE    NERVOUS    SYSTEM. 

tude  with  which  they  perceive  and  record  sensible  phenomena.  This 
was  first  noticed  in  astronomical  observatories,  where  it  was  found 
that  the  passage  of  a  star  across  the  thread  of  a  transit  instrument  was 
differently  recorded  by  different  observers ;  the  difference  sometimes 
amounting  to  as  much  as  one  second.  Subsequent  observations 
showed  that  in  no  case  was  the  time  recorded  with  absolute  accu- 
racy;  but  that  a  certain  delay  always  intervened,  due  to  the  time 
occupied  by  the  nervous  mechanism  of  the  observer.  This  fact  was 
established  by  imitating  the  transit  of  a  star  by  means  of  a  luminous 
point  moving  with  uniform  velocity  before  the  field  of  a  telescope.  I>v 
contrivances  like  those  above  described,  the  real  instant  of  the  passage 
of  the  luminous  point  across  the  thread  of  the  telescope  is  recorded 
upon  a  revolving  cylinder,  and  the  observer  also  marks  its  passage  by 
similar  means.  The  difference  between  the  real  and  the  observed  time 
represents  the  "personal  error"  of  the  observer.  As  it  is  important  to 
eliminate  this  error  from  the  record  of  astronomical  observations,  when 
its  amount  has  been  determined  for  any  particular  observer,  his  record 
is  corrected  by  a  corresponding  quantity.  This  is  termed  the  "personal 
equation  "  of  the  observer. 

The  error  of  any  particular  individual  remains  nearly  the  same,  as 
compared  with  that  of  other  persons;  that  is,  it  will  be  habitually 
greater  or  less  in  one  observer  than  in  another.  But,  like  all  physio- 
logical peculiarities,  it  varies  somewhat  in  the  same  individual;  and 
according  to  Kampf,*  it  may  change  perceptibly  even  in  one  night. 
The  following  table  shows  the  varying  personal  equation  of  two  differ- 
ent observers  in  fractions  of  a  second,  as  ascertained  on  three  successive 

days: 

ABSOLUTE  PERSONAL  EQUATION  01 

Lieut.  Tillman.  I>r.  Karapf. 

May  1 —0.125     .         .  —0.027 

May  2 —0.121     .        .         .       -0.021 

May  3 -0.110     .  -<>.<>2i; 

Where  extreme  accuracy  is  required,  as  in  observations  for  longitude, 
it  is  consequently  recommended  by  Dr.  Kampf  that  the  personal  error 
of  the  observer  be  determined  and  corrected  at  the  time  of  each  obser- 
vation. 


*  On  the  Determination  of  Personal  Equations.   Report  upon  Unhid  Stales  (J 
logical  Surveys  west  of  the  One  Hundndth  Meridian.     Washington,  1877,  p.  -17"). 


CHAPTER    III. 
GENERAL  ARRANGEMENT  OF  THE  NERVOUS  SYSTEM. 

THE  nervous  system,  in  man  and  the  higher  animals,  includes  two 
secondary  systems,  or  groups  of  nervous  centres,  with  their  com- 
missural  fibres  and  peripheral  nerves.  They  are :  first,  the  cerebro- 
spirial  system,  presiding  over  the  functions  of  animal  life ;  and,  sec- 
ondly, the  sympathetic  system,  connected  with  the  internal  acts  of 
nutrition. 

Cerebro- Spinal  System. — Of  the  two  groups  above  mentioned,  the 
cerebro-spinal  system  largely  preponderates  by  its  mass,  the  well- 
marked  distinction  of  its  parts,  and  the  striking  character  of  its  phe- 
nomena. Its  centres  are  also,  in  great  measure,  the  sources  of  func- 
tional activity  for  the  sympathetic  system,  and  thus  control,  directly 
or  indirectly,  the  nervous  relations  of  the  whole  body.  v-As_its  name 
indicates,  the  nervous  centres  belonging  to  it  are  the  brain  and  the 
spinal  cord ;  the  nerves  which  originate  from  them  being  distributed 
to  the  muscles  and  tegumentary  surfaces  of  the  head,  trunk,  and  limbs, 
to  the  organs  of  special  sense,  and  to  the  commencement  and  termina- 
tion of  the  internal  passages  of  the  body. 

In  its  general  form  the  cerebro-spinal  system  is  distinguished  by  a 
nearly  complete  bilateral  symmetry.  Like  the  organs  of  animal  life 
over  which  it  presides,  it  consists  of  a  double  series  of  corresponding 
structures,  united  with  each  other  upon  the  median  line.  This  union 
is  effected  by  transverse  commissures ;  that  is,  by  fibrous  tracts  pass- 
ing from  side  to  side  between  similar  parts  and  enabling  them  to  act 
in  harmony  with  each  other.  The  right  and  left  halves  of  the  brain 
and  spinal  cord,  thus  connected,  furnish  the  nerves  of  sensation  and 
motion  to  the  two  sides  of  the  body. 

Another  peculiarity  of  this  portion  of  the  nervous  system  is  the 
decussation  of  its  fibres.  By  this  term  is  meant  an  oblique  passage 
of  fibres  across  the  median  line,  forming  a  connection  between  dis- 
similar parts  on  the  two  sides;  and  as  this  oblique  crossing  takes 
place  simultaneously  from  right  to  left  and  from  left  to  right,  the  two 
tracts  of  decussating  fibres  are  interwoven  with  each  other  at  the 
median  line.  This  is  most  distinctly  shown  in  the  decussation  of  the 
optic  nerves  at  the  base  of  the  brain  and  in  that  of  the  anterior  pyra- 
mids at  the  medulla  oblongata ;  but  other  instances  occur  at  various 
points  in  the  interior,  and  it  may  be  said,  in  general,  that  the  nerves 
emerging  from  the  right  side  of  the  cerebro-spinal  mass  have  their 

373 


374  THE    NERVOUS    SYSTEM. 

origin  in  the  gray  substance  of  the  left  side,  and  those  emerging  from 
the  left  side  have  their  origin  on  the  right.  The  only  uncertainty  in 
this  respect  is  whether  the  decussation  be  complete  or  partial ;  that  is, 
whether  all  the  fibres  of  a  given  nerve  root  be  connected  with  the 
opposite  side  of  the  central  mass,  or  whether  a  part  of  them  originate 
from  the  same,  and  a  part  from  the  opposite  side.  In  a  large  number 
of  instances  the  decussation  is  anatomically  demonstrated;  in  others 
it  is  inferred  from  the  results  of  experiment.  But  there  can  be  no 
doubt  that  it  is  a  general  feature  in  the  arrangement  of  the  cerebro- 
spinal  system. 

The  spinal  cord  is  the  simplest  and  most  fundamental  part  of  this 
system.  It  is  a  nearly  cylindrical  nervous  mass,  extending  from  its 
junction  with  the  brain  above  to  its  inferior  termination  at  the  level 
of  the  second  lumbar  vertebra.  A  transver.se  section  shows  that  it 

is  incompletely    divided   into 

FlG-  97-  right  and  left   lateral   halves 

by  anterior  and  posterior  me- 
dian fissures ;  of  which  the 
anterior  is  the  wider  and  shal- 
lower, while  the  posterior  is 
narrower  and  deeper.  The 
interior  of  the  cord  consists 
of  gray  substance,  in  the  form 
of  a  double  crescentic-shaped 
mass,  with  the  concavities  of 

TRANSVERSE  SECTION  OF  THE  SPINAL  CORD.-^,  b.  the  Crescents  turned  outward. 

Spinal  nerves  of  right  and  left  sides,    d.  Origin  of  As  these   maSSCS   are   found  at 

anterior  root.    e.  Origin  of  posterior  root.    c.  Gan-  „  ™,rfe  nf  the   onrrl    thev  are 

glion  of  posterior  root.  a11  Par1                           rfl>  tj 

in  reality  elongated  bands  of 

gray  substance,  one  on  each  side  of  the  cord,  running  continuously 
throughout  its  length.  They  are  united  with  each  other  by  a  trans- 
verse band  of  gray  substance,  containing  nerve  fibres,  and  known  as 
the  "gray  commissure,"  in  the  centre  of  which  is  a  narrow  longi- 
tudinal canal,  the  "  central  canal,"  about  0.2  millimetre  in  diameter, 
lined  with  epithelium. 

The  anterior  and  posterior  portions  of  gray  substance,  in  each  lateral 
half  of  the  cord,  are  called  the  anterior  and  posterior  horns.  Imme- 
diately in  front  of  the  gray  commissure  is  a  band  of  white  substance, 
the  "  white  commissure  "  of  the  cord. 

The  spinal  nerves  are  given  off  from  the  cord  at  regular  intervals 
in  symmetrical  pairs  ;  and  are  distributed  to  the  integument  and  muscles 
of  the  corresponding  regions.  In  fish  and  serpents,  where  locomotion 
is  performed  by  lateral  flexion  of  the  spinal  column,  the  cord  is  nearly 
uniform  in  size,  or  tapers  gradually  to  its  posterior  extremity.  But 
in  birds  and  quadrupeds,  where  there  are  special  organs  of  locomo- 
tion, as  fore  and  hind  legs,  or  legs  and  wings,  the  cord  is  increased  in 
size  where  the  nerves  of  these  organs  are  given  off.  In  man,  the  lower 


ARRANGEMENT    OF    THE    NERVOUS    SYSTEM.        375 


cervical  nerves  which  supply  the  arms,  and  the  sacral  nerves  which 
supply  the  legs,  are  larger  than  those  given  off  in  other  regions ;  and 
the  cord  itself  presents  two  enlargements  corresponding  with  the 
origin  of  these  nerves,  namely,  the  cervical  enlargement,  which  is  the 
source  of  the  nerves  for  the  upper  limb,  and  the  lumbar  enlargement, 
which  gives  off  the  nerves  for  the  lower  limb. 

The  origin  of  the  spinal  nerves  on  each  side  of  the  cord  is  by  two 
sets  of  fibres,  forming  anterior  and  posterior  roots.  The  anterior 
root  (Fig.  97,  d)  emerges  from  the  cord  opposite  the  anterior  horn 
of  gray  matter.  The  posterior  root  (e)  originates  at  a  point  corre- 
sponding with  the  posterior  horn  of  gray  matter.  Both  roots  are 
composed  of  numerous  fibres,  united  in  parallel  bundles.  The  posterior 
root  is  distinguished  from  the  anterior  by  the  presence  of  a  small  rounded 
mass  of  gray  matter,  or  ganglion,  beyond  which  the  two  roots  unite 
in  a  common  trunk. 

The  white  substance  of  each  lateral  half  of  the  cord  is  thus  divided 
into  three  portions  or  "  columns ;"  so  called  because  the  nerve  fibres 
composing  them  run,  for  the  most  part,  in  a  longitudinal  direction.  The 
portion  included  between  the  anterior  median  fissure  and  the  anterior 
nerve  roots  is  the  anterior  column;  that  between  the  anterior  and 
posterior  nerve  roots  is  the  lateral  column ;  while  that  between  the 
posterior  nerve  roots  and  the  posterior  median  fissure  is  the  posterior 
column.  As  the  posterior  median  fissure  penetrates  the  cord  quite  to 
the  gray  commissure,  the  posterior  columns  appear  entirely  separated 
from  each  other  in  a  transverse  section ; 
while  the  anterior  columns  are  connected 
by  the  white  commissure  above  mentioned. 

The  brain,  or  "encephalon,"  is  that  por- 
tion of  the  cerebro-spinal  mass  contained 
in  the  cranial  cavity.  It  consists  of  various 
deposits  of  gray  substance,  connected  with 
each  other  and  with  the  spinal  cord  by 
transverse,  oblique,  and  longitudinal  tracts 
of  nerve  fibres.  The  number  and  size  of  its 
nervous  centres  vary  in  different  animals  ac- 
cording to  their  general  bodily  organization, 
and  the  special  development  of  their  ner- 
vous functions. 

In  fish  and  reptiles  the  nervous  centres 
of  the  brain  are  so  distinctly  separated,  and 
of  such  moderate  size,  that  they  are  often 
designated  as  "ganglia."  In  the  alligator 
(Fig.  98)  there  are  five  pairs  of  these  gan- 
glia, arranged  in  a  double  linear  series.  The 
first  are  the  olfactory  ganglia  (u)  which  distribute  their  nerves  to 
the  olfactory  membrane,  and  are  connected  with  the  rest  of  the  brain 
by  slender  longitudinal  tracts  of  white  substance.  The  next  pair  (2>2), 


FIG. 


BRAIN  OF  ALLIGATOR. — 1.  Olfacto- 
ry Ganglia.  2.  Hemispheres.  3. 
Optic  Tubercles.  4.  Cerebellum. 
5.  Medulla  Oblongata. 


376  THE    NERVOUS    SYSTEM. 

somewhat  larger  and  of  triangular  shape,  are  the  "  hemispherical  gan- 
glia," corresponding  to  the  hemispheres,  or  cerebrum  in  the  higher 
classes.  Immediately  following  them  are  two  quadrangular  masses 
(3>3)  which  give  origin  to  the  optic  nerves,  and  are  therefore  called 
the  optic  ganglia;  but  in  some  of  the  higher  animals,  where  they  are 
imperfectly  divided  into  four  nearly  equal  parts,  they  are  known  as  the 
"  tubercula  quadrigemina."  Behind  them  is  a  triangular  collection  of 
nervous  matter  (4),  the  cerebellum.  Finally,  the  upper  portion  of  the 
cord,  just  behind  and  beneath  the  cerebellum,  is  enlarged  into  a  double 
oblong  mass  (65),  the  medulla  oblongata. 

In  birds  the  cerebrum  is  comparatively  larger,  and  nearly  or  quite 
conceals  the  optic  tubercles  in  a  view  taken  from  above.    The  cerebellum 
is  well  developed,  and  presents  on  its  surface  a  num- 
FIG.  99.  ber  Of  transverse  foldings  or  convolutions  by  which 

its  gray  substance  is  increased  in  quantity;  and 
it  extends  so  far  backward  as  to  completely  cover  the 
medulla  oblongata. 

In  quadrupeds,  the  cerebrum  attains  a  still  greater 
size,  as  compared  with  remaining  parts  of  the  brain, 
and  in  the  more  highly  developed  orders  it  is  so  much 
BRAIN  OF  PIGEON.—    increased  as  partly  to  cover  the   olfactory  ganglia 
profile     view.—  i.    jn  front  and  the  cerebellum  behind :  its  surface  at 

Cerebrum.     2.  Optic 

Tubercle.    3.  Cere-    the  same  time  presenting  numerous  convolutions, 
beiium.     4.    Optic    it   also  contains  near  its   base,  on   each   side   the 

Nerve.      5.   Medulla  ,.         ,.  jj.^.         i         n      ,«  /• 

oblongata.  median  line,  two  additional  collections  of  gray  sub- 

stance; namely,  the  "corpora  striata"  and  "optic 
thalami."  These  bodies  are  often  designated  as  the  "  cerebral  ganglia," 
since  they  occupy  the  inferior  parts  of  the  cerebrum,  and  receive  the 
tracts  of  white  substance  entering  it  from  below.  The  cerebellum  in 
quadrupeds  is  enlarged  by  the  development  of  its  lateral  lobes,  and  is 
marked  by  abundant  transverse  convolutions. 

In  man  the  cerebrum  reaches  its  highest  development,  and  prepon- 
derates completely  over  all  the  remaining  nervous  centres.  In  the 
human  brain,  accordingly,  when  viewed  from  above,  there  is  nothing 
to  be  seen  but  the  convoluted  surface  of  the  hemispheres ;  and  even  in 
a  posterior  view  they  cover  everything  but  a  portion  of  the  cerebellum. 
The  remaining  parts,  however,  although  concealed  by  the  cerebrum 
and  cerebellum,  participate  in  the  structure  of  the  encephalon,  forming, 
as  in  the  lower  animals,  a  series  of  associated  nervous  centres,  with 
connecting  tracts  of  nerve  fibres. 

As*  the 'spinal  cord  enters  the  cranial  cavity,  it  enlarges  to  form  the 
medulla  oblongata.  This  portion  of  the  cerebro-spinal  axis  is  dis- 
tinguished from  the  cord  below,  not  only  by  its  form,  but  also  by  the 
arrangement  of  its  gray  and  white  substance.  The  gray  substance, 
which  in  the  cord  presents  on  each  side  the  projections  of  the  anterior 
and  posterior  horns,  recedes,  in  the  medulla  oblongata,  in  a  backward 
direction,  expanding  into  a  continuous  layer  at  its  posterior  surface. 


ARRANGEMENT    OF    THE    NERVOUS    SYSTEM.        877 

At  the  same  time,  the  posterior  columns  of  white  substance  diverge 
at  an  acute  angle,  leaving  between  them  the  fourth  ventricle,  and,  under 
the  name  of  the  restiform  bodies,  become  continuous  with  the  inferior 
peduncles  of  the  cerebellum. 

In  front,  the  medulla  oblongata  presents  two  longitudinal  eminences 
of  white  substance,  one  on  each  side  of  the  median  line,  the  anterior 
pyramids,  which  take  the  place  of  the  anterior  columns  of  the  cord. 
At  their  lower  portion  they  exhibit  the  well-known  decussation,  formed 
by  oblique  bundles  of  fibres  crossing  the  median  line  from  below  upward 
and  from  side  to  side.  Thus  the  right  anterior  pyramid  is  formed  of 
fibres  which  come  from  the  left  side  of  the  cord,  and  the  left  anterior 
pyramid  of  those  which  come  from  the  right  side  of  the  cord. 

FIG.  100. 


MEDULLA  OBLONGATA  AND  BASE  OP  THE  BRAIN  IN  MAN.— 1 .  Decussation  of  the  Optic  Nerves. 
2,  2.  Middle  Lobes  of  the  Cerebrum.  3,  3.  Crura  Cerebri.  4.  Tuber  Annulare.  5,  5.  Lateral  Lobes 
of  the  Cerebellum.  6.  Anterior  Pyramid.  7.  Olivary  Body.  8.  Restiform  Body.  (Hirschfeld.) 

Immediately  outside  the  pyramids  are  two  elongated  oval  masses, 
the  olivary  bodies,  which  consist  externally  of  white  substance,  but 
internally  contain  a  thin  convoluted  layer  of  gray  substance,  resembling 
in  miniature  the  convolutions  of  the  hemispheres.  They  are  special 
deposits  of  gray  substance  in  the  medulla  oblongata,  superadded  to  the 
rest,  and  not  continuous  with  that  of  the  spinal  cord. 

At  the  upper  limit  of  the  medulla  oblongata  is  the  tuber  annulare,  so 
called  because  it  forms  a  ring-like  protuberance  at  the  base  of  the  brain. 
Superficially,  it  consists  of  transverse  bundles  of  fibres  passing  over, 
in  an  arched  form,  from  one  side  of  the  cerebellum  to  the  other.  Where 
they  cross  the  tuber  annulare  these  fibres  constitute  the  "  pons  Yarolii ;" 


378  THE    NERVOUS    SYSTEM. 

at  the  sides,  where  they  turn  backward,  they  form  the  "middle  peduncles 
of  the  cerebellum." 

In  its  deeper  parts,  the  tuber  annulare  contains  longitudinal  tracts  of 
white  substance,  passing  upward  from  the  medulla  oblongata  toward 
the  cerebrum.  The  continuation  of  the  anterior  pyramids  in  front,  and 
the  remaining  longitudinal  bundles  of  the  medulla  oblongata  behind, 
pass  into  and  through  the  tuber  annulare,  between  various  irregularly 
diffused  deposits  of  gray  substance.  From  the  upper  border  of  the 
tuber  annulare,  they  emerge  in  the  form  of  two  obliquely  diverging 
bundles  of  nerve  fibres,  the  crura  cerebri,  or  peduncles  of  the  brain. 
They  are  joined  posteriorly  by  other  longitudinal  bundles  coming  from 
the  cerebellum,  known  as  the  " anterior  peduncles  of  the  cerebellum," 
and  forming  the  tracts  of  communication  between  the  cerebellum  and 
the  cerebrum.  The  crura  cerebri  then  pass  into  the  base  of  the  brain, 
thus  completing  its  connection  with  the  spinal  cord. 

The  structure  of  the  cerebro-spinal  axis,  as  a  whole,  may  be  described 
as  follows :  There  is  a  continuous  tract  of  gray  substance,  surrounding 
the  central  canal  of  the  spinal  cord,  expanding  into  a  superficial  layer 
on  the  floor  of  the  fourth  ventricle,  and  thence  extending  forward 
around  the  aqueduct  of  Sylvius  and  on  the  vertical  sides  of  the  third 
ventricle,  until  it  terminates  at  the  infundibulum.  This  is  the  "  gray 
substance  of  the  medullary  canal,"  and  from  it  all  the  nerves  of  volun- 
tary motion  and  general  sensibility  take  their  origin.  Near  its  upper 
part  there  are  various  additional  deposits  of  gray  substance,  the  largest 
of  which  is  the  cerebellum ;  and  beyond  its  upper  extremity  is  the 
cerebrum,  containing  the  cerebral  ganglia  at  its  base,  and  expanding 
above  into  the  convolutions  of  the  hemispheres.  The  two  hemi- 
spheres are  connected  with  each  other  by  a  broad  transverse  commis- 
sure of  white  substance,  the  "corpus  callosum,"  covering  the  lateral 
ventricles  and  the  cerebral  ganglia;  and  the  two  lateral  halves  of 
the  cerebellum  are  united  in  a  similar  way  by  the  pons  Yarolii. 

The  longitudinal  connections  of  the  cerebro-spinal  axis  are  the  con- 
tinuations of  the  columns  of  the  cord.  On  emerging  from  the  tuber 
annulare,  under  the  form  of  the  crura  cerebri,  they  enter  the  base  of  the 
brain,  and  meet  at  once  with  the  gray  substance  of  the  cerebral  ganglia. 
They  pass  through  and  between  these  ganglia,  forming  in  this  situation 
the  so-called  "  internal  capsule;"  and  from  its  upper  border  they  spread 
out  on  each  side  into  an  expanding  crown  of  divergent  fibres,  known 
as  the  "corona  radiata."  The  fibres  of  the  corona  radiata  thence  dis- 
perse in  every  direction,  to  reach,  at  last,  the  gray  matter  of  the  cere- 
bral convolutions. 

It  is  by  no  means  certain  that  the  individual  nerve  fibres  are  con- 
tinuous throughout  these  longitudinal  connections.  On  the  contrary, 
the  study  of  succes>i\  e  microscopic  sections,  by  the  best  observers,  has 
failed  to  show  such  a  direct  continuity;  and  it  is  considered  more  prob- 
able that  the  fibres  coming  from  one  portion  of  the  cerebro-spinal  axis 
terminate  in  certain  deposits  of  gray  substance,  and  that  the  connec- 


ARRANGEMENT  OF  THE  NERVOUS  SYSTEM.    379 

tion  is  continued  by  new  fibres  originating  from  the  same  or  adjacent 
cells.     According  to  this  view,  the  longitudinal  tracts  consist  of  fibres 

FIG.  101. 


IGRAM  OP  HUMAN  BRAIN  IN  TRANSVERSE  VERTICAL  SECTION.— 1.  Tuber  Annulare;  2,2. 
Crura  Cerebri.  3,  3.  Internal  Capsule.  4,  4.  Corona  Radiata.  5,  6.  Cerebral  Ganglia.  7.  Corpus 
Callosum. 

which  are  interrupted  in  their  course  by  different  deposits  of  gray  sub- 
stance ;  so  that  an  impression  or  impulse  conveyed  from  one  region  to 
another  is  not  the  same  throughout,  but  is  modified  in  character  by  the 
nervous  centres  which  successively  receive  and  transmit  it.  How  many 
such  interruptions  there  may  be  in  the  transmission  of  nervous  impulses 
is  not  known  ;  but  it  must  be  considered  that,  for  ordinary  motor  and 
sensitive  acts,  there  are,  counting  from  without  inward,  three  successive 
nervous  centres  through  which  they  pass ;  namely, 

1st.  The  gray  substance  of  the  medullary  canal ; 

2d.  The  cerebral  ganglia  at  the  base  of  the  brain  ;  and 

3d.  The  convolutions  of  the  hemispheres. 

There  are  also  three  sets  of  fibres  in  the  longitudinal  connecting 
tracts : 

1st.  The  nerves  and  nerve  roots,  connecting  the  peripheral  organs 
with  the  gray  substance  of  the  medullary  canal ; 

2d.  The  columns  of  the  cord  and  the  crura  cerebri,  connecting  the 
gray  substance  of  the  medullary  canal  with  the  cerebral  ganglia ;  and 

3d.  The  fibres  of  the  corona  radiata,  connecting  the  cerebral  ganglia 
with  the  convolutions  of  the  hemispheres. 

Thus  between  the  cerebral  convolutions  and  the  peripheral  organs 
are  two  intermediate  stations  of  nervous  matter ;  namely,  the  cerebral 
ganglia  and  the  gray  substance  of  the  medullary  canal ;  and  when  a 
nervous  impulse  passes  from  the  cerebral  convolutions  to  the  peripheral 


380  THE    NERVOUS    SYSTEM. 

organs,  or  vice  versa,  three  successive  sets  of  nerve  fibres  take  part  in 
its  transmission. 

In  each  separate  region  of  the  cerebro-spinal  system,  furthermore, 
the  gray  substance  may  act  as  a  nervous  centre,  to  transform  sensitive 
impressions  into  a  motor  impulse,  and  thus  give  rise  to  reflex  action. 
Such  a  reflex  action  may  take  place  in  the  nervous  centre  nearest  the 
periphery,  without  calling  into  operation  any  other  than  its  own  special 
endowments,  and  without  presenting  any  character  of  consciousness 
or  volition.  But  the  sensitive  impression  may  also  be  transmitted 
through  the  whole  series  of  longitudinal  connections  to  the  cortex 
of  the  brain ;  and  the  motor  impulse  thus  excited  may  pass  in  the 
reverse  direction  through  its  entire  route  to  the  muscles  of  the  limbs. 
The  convoluted  layer  of  gray  substance  in  the  cerebral  hemispheres 
serves  therefore  as  a  great  concave  mirror,  by  which  impressions 
coming  from  without  are  received  as  conscious  sensations  and  ideas, 
and  reflected  in  the  form  of  intelligent,  voluntary  acts.  To  produce 
this  result,  the  whole  mechanism  of  the  cerebro-spinal  system  is  called 
into  operation,  each  part  acting  in  succession,  to  modify  or  transmit  the 
nervous  impulse. 


CHAPTER  IV. 
THE  SPINAL  COED. 

THE  spinal  cord  is  that  part  of  the  cerebro-spinal  system  contained 
in  the  spinal  canal,  and  which  sends  its  nerves  to  the  muscles  and 
integument  of  the  trunk  and  limbs.  It  consists  externally  of  white 
substance,  forming  longitudinal  tracts  of  nerve  fibres,  the  continuations 
of  which  make  connection  with  the  brain  above  ;  and  internally  of  gray 
substance  surrounding  its  central  canal,  and  occupying  the  interior  of 
its  lateral  halves.  It  is  therefore  constituted  to  act  in  a  double  capac- 
ity :  First,  as  a  medium  of  communication  between  the  brain  and  the 
peripheral  organs ;  and  secondly,  as  an  independent  nervous  centre, 
with  special  endowments  of  its  own. 

Arrangement  of  Gray  and  White  Substance  in  the  Spinal  Cord. 

The  relations  of  the  gray  and  white  substance  form  the  necessary 
basis  for  a  physiological  anatomy  of  this  part  of  the  nervous  system. 
The  connections  of  the  nerve  fibres  with  the  gray  substance,  and  their 
course  in  the  longitudinal  columns,  are  the  most  important  for  this 
purpose.  These  relations  are  not  fully  known ;  but  much  has  been 
accomplished  in  this  respect  by  the  examination  of  transverse  and  lon- 
gitudinal sections  of  the  cord,  either  in  the  fresh  condition  or  after 
the  use  of  hardening  and  staining  preparations.  The  size  and  form 
of  the  cord,  as  well  the  quantity  and  configuration  of  its  white  and 
gray  substance,  vary  much  in  its  different  parts.  In  the  upper  cervical 
region,  it  is  nearly  cylindrical ;  at  the  cervical  enlargement,  it  is 
widened  laterally,  and  flattened  in  an  antero-posterior  direction ;  in 
the  dorsal  region,  it  again  approximates  the  cylindrical  form,  but  is 
reduced  in  size ;  its  second  enlargement  is  at  the  beginning  of  the 
lumbar  region  ;  after  which  it  diminishes  rapidly  to  its  termination. 
It  is  evident  from  an  inspection  of  its  section  surfaces  at  different 
levels,  that  the  cervical  and  lumbar  enlargements  are  mainly  due  to 
an  increased  quantity  of  gray  substance  in  these  regions  ;  and  that  the 
white  substance,  on  the  whole,  diminishes  gradually  from  above  down- 
ward. This  agrees  with  the  double  physiological  character  of  the  cord ; 
its  gray  substance  acting  as  a  nervous  centre  for  the  corresponding 
regions  of  the  body,  while  its  white  substance,  at  any  one  point,  rep- 
resents the  tracts  of  communication  for  nerves  given  off  below. 

The  Gray  Substance. — The  gray  substance  in  the  spinal  cord,  as 
elsewhere,  is  a  mixture  of  nerve  cells  and  nerve  fibres,  of  which  the 
nerve  cells  are  the  distinctive  element.  They  are  all  provided  with 

381 


382 


THE    NERVOUS    SYSTEM. 


nr 


cell  processes  running  in  various  directions,  most  of  them  exhibiting 
abundant  ramifications,  while  some  continue  their  course  for  a  con- 
siderable distance  undivided,  and  assume  at  last  the  appearance  of 
axis  cylinders.  The  largest  and  most  remarkable  are  situated  in  the 
anterior  horns,  where  they  reach  the  size  of"  from 
07  to  135  mmm.  in  diameter;  many  of  them 
being  the  largest  known  cells  in  the  nervous 
system.  They  are  mainly  arranged  on  each  side 
in  three  groups,  namely,  at  the  point,  and  at  the 
external  and  internal  borders  of  the  anterior  horn. 
Throughout  the  dorsal  region  there  is  a  group  of 
similar  cells  at  the  base  of  each  posterior  horn,  known 
as  the  "  column  of  Clarke,"  extending  from  the 
lower  cervical  region  nearly  to  the  lumbar  enlarge- 
ment. Here  these  cells  disappear  as  a  distinct 
group,  while  those  of  the  anterior  horns  increase 
considerably  both  in  numbers  and  size.  Elsewhere 
throughout  the  gray  substance,  but  especially  in 
the  posterior  horns,  the  nerve  cells  are  much 
smaller,  but  similar  in  form,  and  provided  with 
branching  prolongations.  The  anterior  and  pos- 
terior horns  are  not  therefore  absolutely  distin- 
guished from  each  other  by  the  size  of  their  nerve 
cells,  but  only  by  the  relative  abundance  of  the 
larger  and  smaller  varieties  ;  since  a  few  large  cells 
are  found  in  the  posterior  horns,  and  the  smaller 
cells  exist  in  both  regions. 

The  nerve  fibres  of  the  gray  substance  are,  in 
general,  much  smaller  than  those  of  the  white 
substance,  but  otherwise  present  the  same  ana- 
tomical characters.  Most  of  them  run  horizon- 
tally, in  a  transverse,  antero-posterior,  or  radi- 
ating direction.  They  consist,  first,  of  fibres  which 
have  penetrated  the  gray  substance  from  the  ante- 
rior and  posterior  nerve  roots ;  secondly,  of  fibres 
which  cross  the  median  line  in  the  gray  cominis- 

TIIK  SPINAL  CORD  IN  ,     ,,     .      f  ,    ,     ,  .     ,    ,,  , 

MAX.— i.  Upper  cervi-    sure>  ^otn  m  front  and  behind  the  central  canal, 
cai  Region,   ii.  Lower    forming  a  commissural  connection  between  the  two 

<Vrvical  Region.     III.     ,    ,         ,  ,     ,  „    ,,  ,     ,,  .    ,, 

i»..raai    Region,    iv.   lateral  halves  of  the  gray  substance;  and,  thirdly, 
Lumbar  Enlargement,    of  fibres  which  run  in  a  great  variety  of  directions, 

V.  Lower  Ex  tiremity.  j      r       i  •   i      AI  ••  j    ^  •       A- 

and  of  which  the  origin  and  terminations  are  uu- 
knou  n. 

The  Wliite  Substance. — The  white  substance  of  the  spinal  cord  con- 
sists of  nerve  fibres,  tin-  large  majority  of  which  run  in  a  longitudinal 
direction,  forming  tracts  or  "columns,"  designated,  according  to  their 
situation,  as  the  anterior,  lateral,  and  posterior  columns  of  the  cord. 
In  microscopic  transverse  sections  of  the  cord,  treated  by  hardening 


THE    SPINAL    CORD. 


383 


and  staining  preparations,  the  longitudinal  fibres  present  the  appear- 
ance of  minute  cylinders  cut  across ;  while  those  which  are  horizontal 


FIG.  103. 


TRANSVERSE  SECTION  OF  THE  SPINAL  CORD  IN  MAN  ;  lumbar  region. 

oblique  are  seen  in  profile  for  a  longer  or  shorter  distance  in  the 
section. 

The  anterior  column,  included  between  the  anterior  median  fissure 
and  the  anterior  nerve  roots,  consists  in  great  measure  of  fibres  from 
the  anterior  horn  of  gray  substance  on  the  opposite  side.  The  trans- 
verse band  of  white  substance,  at  the  bottom  of  the  anterior  median 
fissure,  is  known  as  the  white  commissure;  but  this  name  is  not 
entirely  appropriate,  since  the  fibres  in  question  do  not  connect  corre- 
sponding parts  on  the  two  sides.  Those  joining  the  right  anterior 
column  come  from  the  gray  substance  of  the  left  anterior  horn ;  and 
those  which  enter  the  left  anterior  column  come  from  the  gray  sub- 
stance of  the  right  anterior  horn.  The  so-called  white  commissure 
is  therefore  in  reality  a  decussation,  connecting  the  anterior  columns 
on  each  side  with  the  gray  substance  of  the  opposite  side  of  the  cord. 

The  lateral  column,  occupying  the  space  between  the  anterior  and 
posterior  nerve  roots,  derives  its  fibres  from  two  sources.  First,  from 
the  whole  external  border  of  the  anterior  horn  and  a  small  part  of  the 
posterior  horn.  The  mode  of  origin  of  these  fibres  in  the  gray  sub- 
stance is  unknown  ;  but  they  pass  out  from  it  horizontally  and  obliquely 
and  then  become  parallel  with  the  remaining  longitudinal  fibres  of 
the  lateral  column.  Secondly,  from  the  anterior  nerve  roots ;  some  of 
whose  fibres,  after  traversing  the  gray  substance  of  the  anterior  horn, 
pass  out  from  it  in  a  lateral  direction  like  those  just  described,  and  join 
the  lateral  column.  At  each  level,  therefore,  although  the  great  mass 
of  fibres  in  the  lateral  column  are  longitudinal,  there  are  always  some 
which  are  oblique,  emerging  from  the  gray  substance,  to  become  longi- 
tudinal at  a  higher  point. 


384  THE     NERVOUS     S  Y  S  T  F.  M  . 

The  posterior  column,  limited  by  the  posterior  median  fissure  inter- 
nally and  by  the  posterior  nerve  roots  externally,  also  consists  of  fibres 
from  two  sources — namely,  first,  fibres  coming  from  the  inner  border 
of  the  posterior  horn,  the  origin  of  which  cannot  be  more  precisely 
determined  ;  and  secondly,  fibres  coming,  through  the  gray  commissure, 
from  the  opposite  side  of  the  cord.  According  to  Huguenin,*  the 
posterior  columns  are  formed  altogether  of  these  two  sets  of  fibres, 
and  do  not  receive  any  from  the  posterior  nerve  roots. 

Connection  of  the  Nerve  Roots  with  the  Spinal  Cord. — The  anterior 
nerve  roots  enter  the  spinal  cord  in  a  number  of  distinct  bundles,  which 
pass  horizontally  backward  between  the  longitudinal  fibres  of  the  white 
substance  and  reach  the  gray  substance  of  the  anterior  horn.  Here 
their  fibres  spread  out  in  a  variety  of  directions ;  some  of  them  passing 
inward,  some  outward,  and  some  almost  directly  backward.  The  exact 
termination  of  these  fibres  has  not  been  determined,  except  for  a  part 
of  their  number.  All  observers  are  agreed  that  some  of  the  root  fibres 
are  directly  connected  with  large  nerve  cells  in  the  anterior  horn ; 
and  according  to  Huguenin,  each  one  of  the  three  groups  of  cells  in 
this  situation  receives  such  communicating  fibres.  A  second  portion 
of  the  anterior  root  fibres,  described  by  Kolliker,f  and  accepted  by 
others,  after  running  outward  to  the  external  border  of  the  anterior 
horn,  pass  into  the  white  substance,  and,  turning  upward,  become 
part  of  the  longitudinal  fibres  of  the  lateral  column.  A  third  portion 
still  is  composed  of  fibres  which  run  directly  backward  toward  the 
posterior  horn,  but  whose  termination  is  unknown. 

The  fibres  of  the  posterior  nerve  roots  penetrate  the  cord  in  one  or 
two  principal  bundles,  and  pass  immediately  to  the  gray  substance  of 
the  posterior  horn.  Here  some  of  them  curve  inward,  assume  a  trans- 
verse direction,  and  cross  the  median  line,  in  the  gray  commissure,  to 
the  opposite  side  of  the  cord.  Others  become  lost  in  the  gray  substance 
of  the  posterior  horn  and  the  base  of  the  anterior  horn,  without  its 
being  possible  to  ascertain  their  exact  destination  ;  since  the  connection 
of  nerve  fibres  with  nerve  cells  is  not  seen  in  the  posterior  horns. 
Finally,  a  third  portion  of  these  fibres,  according  to  Kolliker,  change 
their  direction  and  become  longitudinal,  still  remaining  in  the  gray 
substance  and  continuing  their  course  in  this  direction  for  an  unknown 
distance. 

The  anterior  and  posterior  nerve  roots,  accordingly,  resemble  each 
other  in  one  respect,  namely,  that  their  immediate  destination  in  the  cord 
is  the  gray  substance  of  the  corresponding  horns.  But  the  fibrrs  of  the 
anterior  root  unite  with  nerve  cells  in  the  anterior  horn,  or  join  the 
longitudinal  tract  of  the  lateral  column;  while  those  of  the  posterior 
root  show  no  direct  connection  with  nerve  cells,  but  partly  cross  to  the 


»  Anatomic  dcs  Centres  Nerveux.     Paris,  1879,  i>.  -JM. 
f  Klt'im-nts  <riIi-toloKu-  Humuine.     Paris,  1868,  p.  344. 


THE    SPINAL     CORD. 


385 


FIG.  104. 


opposite  side  in  the  gray  commissure,  and  partly  become  longitudinal 
in  the  gray  substance  of  the  same  side. 

Connections  of  the  Spinal  Cord  with  the  Brain. 

The  connections  of  the  spinal  cord  with  the  brain  take  place  by  a  con- 
tinuation of  the  fibres  of  its  longitudinal  columns,  through  the  medulla 
oblongata  and  tuber  annulare.  But  this  continuation  is  not  entirely  a 
simple  one,  since  the  fibres  of  the  various  columns  shift  their  position 
at  the  level  of  the  medulla  oblongata,  and  also  exhibit  at  one  point  or 
another  more  or  less  complete  decussations. 

Decussation  of  the  Pyramids. — Throughout  the  greater  portion  of 
the  cord,  its  columns  are  formed  almost  exclusively  of  longitudinal 
fibres,  and  each  column,  examined  in  successive  sections,  retains  its 
special  form  and  position.  But  in  the  upper  cervical  region  a  change 
begins  to  show  itself  by  which  the  fibres  from  the  inner  and  posterior 
parts  of  the  lateral  column  are  directed  obliquely  inward  and  forward, 
through  the  base  of  the  anterior  horn  of  gray  matter  and  behind  the 
anterior  column  of  the  same  side.  Above  the  level  of  the  second  cer- 
vical vertebra  this  change  increases  in  extent,  so  that  bundles  of  fibres 
from  the  lateral  column  pass  obliquely  forward  and  upward,  across  the 
median  line,  to  the  opposite  border  of  the  anterior  median  fissure ;  thus 
taking  the  place,  immediately  next  this  fissure,  previously  occupied  by 
the  anterior  column.  As  the 
same  thing  happens  on  both 
sides,  there  appear,  in  the  lower 
part  of  the  medulla  oblongata,  at 
the  bottom  of  the  anterior  median 
fissure,  alternating  bundles  of 
fibres,  successively  crossing  from 
left  to  right  and  from  right  to 
left.  This  is  the  decussation  of 
the  anterior  pyramids;  and 
after  its  completion  these  bodies 
appear  as  two  longitudinal  bun- 
dles, next  the  anterior  median 
fissure,  and  running  forward  to 

the   tuber   annulare.      The   ante-  TRANSVERSE  SECTION  OF  HUMAN  SPINAL  CORD  ;  at 
,.       ,  the  lower  extremity  of  the  decussation  of  the 

rior   pyramids   accordingly   are    pyramids. 
not  continuations   of  the  ante- 
rior columns  of  the  cord,  although  placed  above  them  in  linear  series. 
Their  fibres  are  derived  mainly  from  the  lateral  columns  of  the  oppo- 
site side ;  and  they  form,  in  the  lower  part  of  the  medulla  oblongata, 
a  decussation  which  is  visible  externally  because  it  takes  place  by  distinct 
bundles  of  considerable  size,  alternating  with  each  other  on  the  median 
line. 

This  transfer  of  fibres  from  the  lateral  columns  to  the  anterior  pyra- 
mids, next  the  median  fissure,  accounts  for  the  change  in  form  of  the 

Z 


386  THE    NERVOUS    SYSTEM. 

cord  while  passing  from  the  cervical  region  to  the  medulla  oblonjrata. 
At  the  cervical  enlargement  in  the  lower  part  of  the  neck  (Fig.  102,  II.) 
the  cord  is  very  wide  transversely,  owing  partly,  no  doubt,  to  the  root 
fibres  of  the  great  nerves  of  the  brachial  plexus,  which  have  joined  the 
lateral  columns  after  traversing  the  gray  substance  of  the  anterior 
horn.  But  at  the  upper  extremity  of  the  cord  (Fig.  102,  I.)  its  trans- 
verse diameter  diminishes  and  its  antero-posterior  diameter  increases  ; 
since  some  of  its  fibres  have  left  the  lateral  column  to  reach  an  anterior 
position  on  the  opposite  side. 

Beside  the  decussating  fibres  of  the  pyramids  derived  from  the  lateral 
columns  of  the  cord  there  are  others  which  come  from  the  posterior 
columns  and  the  posterior  horns  of  gray  substance.  The  change  in 
direction  of  these  fibres  takes  place  at  a  little  higher  level  than  that 
just  described.  It  forms  the  upper  portion  of  the  decussation  of  the 
pyramids.  The  fibres,  after  leaving  the  posterior  columns  and  horns, 
run  forward  and  inward,  cross  the  median  line  obliquely,  like  the  pre- 
ceding, and  then  join  the  anterior  pyramids,  forming  their  deeper  and 
more  lateral  portions.  As  the  pyramids  reach  the  tuber  annulare, 
therefore,  they  are  composed  superficially  and  toward  the  median  line 
of  fibres  from  the  opposite  lateral  columns  of  the  cord ;  while  their 
deep-seated  and  external  fibres  come  from  the  opposite  posterior  col- 
umns and  horns. 

The  further  continuation  of  the  anterior  pyramids  is  through  the 
tuber  annulare  into  the  crura  cerebri,  of  which  they  form  the  lower- 
most or  superficial  portion.  This  part  of  the  crus  cerebri,  which  is  that 
visible  at  the  base  of  the  brain,  sends  its  fibres  mainly  forward,  upward, 
and  outward,  into  the  substance  of  the  corpus  striatum.  But  accord- 
ing to  Huguenin  a  portion  of  the  fibres  on  its  external  border,  repre- 
senting those  which  have  come  from  the  posterior  columns  and  horns, 
pass  behind  the  cerebral  ganglia  to  reach  the  convolutions  of  the  oc- 
cipital lobe. 

Deep-seated  Portion  of  the  Crura  Cerebri. — The  deep-seated  or 
uppermost  portion  of  the  crura  cerebri,  is  formed  of  fibres  from  the 
anterior  columns  of  the  cord,  and  from  the  anterior  part  of  the  lateral 
columns.  The  anterior  columns  of  the  cord  are  contiguous  to  the 
median  fissure  until  their  place  is  taken,  as  above  described,  by  the 
obliquely  decussating  bundles  of  the  anterior  pyramids.  In  the  me- 
dulla oblongata,  they  thus  come  to  be  placed  farther  outward  and 
1  >ack ward,  and  in  passing  through  the  tuber  annulare  they  occupy  a 
deep-seated  position  in  its  interior.  Thence  they  run  forward  in  the 
ii] (per  or  deep-seated  portion  of  the  crura  cerebri,  and  pass  to  the  optic 
thalami.  The  remaining  fibres  of  the  lateral  colt/nr/i,  which  have  not 
taken  part  in  the  formation  of  the  pyramids,  continue  their  course 
upward,  pass  through  the  medulla  oblongata  and  tuber  annulare,  and, 
finally,  joining  the  deep-seated  portion  of  the  crura  cerebri,  reach  in 
this  way  the  optic  tlialaini. 

Inferior  Peduncles  of  the  Cerebellum. — The  inferior  peduncles  of 


THE    SPINAL    CORD.  387 

the  cerebellum,  or  the  "restiform  bodies,"  are  continuations  from  the 
main  part  of  the  posterior  columns  of  the  cord.  As  these  columns 
diverge  from  each  other  at  the  medulla  oblongata,  leaving  between 
them  the  space  of  the  fourth  ventricle,  they  present  the  superficial 
appearance  of  passing  directly,  on  each  side,  from  the  cord  to  the  cere- 
bellum. But  while  all  admit  that  a  portion  of  each  restiform  body  is 
derived  from  the  posterior  column  of  the  cord,  observers  differ  as  to 
which  portion  is  so  derived ;  and  according  to  the  views  of  Clarke  and 
Meynert,*  the  greater  part  undergo  decussation  in  the  interior  of  the 
medulla  oblongata,  so  that  the  restiform  body  of  the  right  side  is 
formed  of  fibres  from  the  left  posterior  column,  and  vice  versa. 

The  connections  of  the  spinal  cord  with  the  brain,  so  far  as  they  are 
known  with  certainty,  may  be  accordingly  stated  as  follows  : 

1.  The  greater  part  of  the  lateral  columns,  and  a  portion  of  the  pos- 
terior columns,  after  bilateral  decussation,  form  the  anterior  pyramids, 
which  are  continued  in  the  superficial  portion  of  the  crura  cerebri  to 
the  corpora  striata. 

2.  The  remainder  of  the  lateral  columns,  together  with  the  anterior 
columns,  pass  by  the  deep-seated  portion  of  the  crura  cerebri  to  the 
optic  thalami. 

3.  The  main  portion  of  the  posterior  columns,  perhaps  after  decus- 
sation in  the  medulla  oblongata,  appear  in  the  restiform  bodies,  and 
thus  reach  the  cerebellum. 

Transmission  of  Motor  and  Sensitive  Impulses  in  the  Spinal  Cord  and 

Nerves, 

The  methods  adopted  for  determining  the  functions  of  particular  tracts 
of  the  nervous  system  are  twofold  ;  first,  by  applying  an  artificial  stim- 
ulus to  the  nerve  or  nervous  tract,  and  observing  the  effect  produced ; 
secondly,  by  observing  what  nervous  function  is  abolished  when  the 
tract  is  divided  or  destroyed.  In  the  peripheral  nerves,  which  are 
simply  organs  of  transmission,  both  these  methods  yield  definite  results. 
In  the  central  parts,  they  are  sometimes  complicated  by  the  mutual  rela- 
tions of  the  gray  and  white  substances. 

Motor  and  Sensitive  Transmission  in  the  Spinal  Nerves  and  Nerve 
Hoots. — If,  in  a  living  animal,  a  mechanical  or  galvanic  stimulus  be 
applied  to  the  anterior  root  of  a  spinal  nerve,  the  effect  of  this  irrita- 
tion is  a  convulsive  movement  of  the  part  to  which  the  nerve  is  dis- 
tributed. The  muscular  action  is  instantaneous,  involuntary,  and 
momentary  in  duration ;  and  it  is  repeated  with  mechanical  precision 
each  time  the  stimulus  is  applied.  It  is  usually  unaccompanied  by  any 
indication  of  sensibility,  and  it  is  evidently  a  direct  result  of  the  excite- 
ment of  the  anterior  root.  This  root  is  therefore  said  to  be  "  excitable," 
because  its  irritation  excites  a  movement  in  the  corresponding  parts. 

Furthermore,  if  the  anterior  root  of  a  spinal  nerve  be  divided,  while 

*Huguenin.     Anatomic  des  Centres  Nerveux.     Paris,  1879,  p.  233. 


388  THE    NERVOUS    SYSTEM. 

the  remaining  nervous  connections  are  left  untouched,  the  result  is  an 
immediate  and  total  paralysis  of  voluntary  movement  in  the  muscles 
to  which  that  nerve  is  distributed.  At  the  same  time,  the  power  of 
sensibility  is  undiminished,  and  the  animal  is  still  capable  of  feeling 
the  contact  of  foreign  bodies  or  a  galvanic  current  applied  to  the  skin. 
If  the  anterior  roots  of  a  series  of  spinal  nerves  be  thus  divided,  as, 
for  example,  those  of  all  the  lumbar  and  sacral  nerves  on  one  side,  the 
above  effect  wilt  be  produced  for  the  entire  corresponding  region  of  the 
body,  and  the  whole  posterior  limb  on  that  side  will  lose  the  power  of 
voluntary  motion  while  retaining  its  sensibility.  This  is  not  due  to 
any  loss  of  physiological  properties  in  either  the  nerve  or  the  muscles, 
since  irritation  of  the  nerve  or  nerve  root,  outside  the  point  of  section, 
still  produces  muscular  contraction  as  before.  All  these  facts  prove 
that  the  path  by  which  impulses  for  voluntary  motion  pass,  from  the 
spinal  cord  to  a  muscle,  is  exclusively  the  anterior  root  of  the  spinal 
nerve. 

On  the  other  hand,  if  the  posterior  root  be  irritated,  a  sensation  is 
produced,  more  or  less  acute,  according  to  the  amount  and  quality  of 
the  irritation.  This  sensation,  when  of  a  certain  intensity,  is  accom- 
panied by  movements.  But  these  movements  are  of  a  reflex  character, 
and  not  necessarily  confined  to  the  part  to  which  the  nerve  is  distrib- 
uted ;  and  if  the  corresponding  anterior  root  have  been  divided,  this 
part  will  remain  motionless,  while  muscular  contractions  continue  to 
be  produced  elsewhere.  Such  movements,  accordingly,  are  not  pro- 
duced directly  by  irritation  of  the  posterior  root,  but  are  caused  indi- 
rectly by  the  reaction  of  the  nervous  centres.  The  only  immediate 
result  of  irritation  of  a  posterior  nerve  root  is  a  sensation,  and  this  root 
is  therefore  said  to  be  "  sensitive." 

Moreover,  if  the  posterior  root  be  divided,  the  consequence  is  a  loss 
of  sensation  in  the  corresponding  region  of  the  body.  This  is  due 
simply  to  the  rupture  of  communication  between  the  integument  and 
the  nervous  centres ;  since  irritation  of  that  part  of  the  divided  nerve 
which  is  still  attached  to  the  spinal  cord  produces  a  sensation  as  before. 
The  posterior  root  of  the  spinal  nerve  is,  therefore,  in  this  part  of  the 
nervous  system,  the  exclusive  channel  of  transmission  for  sensitive 
impressions. 

But  beyond  the  situation  of  the  spinal  ganglia,  the  two  roots  unite 
in  a  common  trunk.  Here,  the  fibres  of  the  anterior  and  posterior 
roots  become  so  intermingled  that  they  can  no  longer  be  separately 
irritated  by  artificial  means.  They  pass,  still  associated  in  this  manner, 
into  the  branches  and  subdivisions  of  the  nerve  ;  and  only  separate  from 
each  other  again  at  its  terminal  ramifications,  where  the  sensitive  fibres 
are  distributed  to  the  integument  and  the  motor  fibres  to  the  muscles. 

A  spinal  nerve,  therefore,  in  its  trunk  and  peripheral  branches,  con- 
tains both  sensitive  and  motor  fibres,  and  is  consequently  a  "  mixed  " 
nerve.  It  is  both  excitable  and  sensitive,  since  its  artificial  irritation 
causes  at  the  same  time  sensation  and  movement ;  and  if  it  be  divided, 


THE    SPINAL    CORD.  389 

the  injury  is  followed  by  loss  of  both  sensibility  and  voluntary  motion 
in  the  corresponding  parts.  It  is  also  an  important  fact  that,  in  these 
instances  of  section  of  the  trunk,  branches,  or  roots  of  a  spinal  nerve, 
the  consequent  loss  of  sensibility  or  motion  is  persistent,  so  long-  as  the 
injury  lasts.  The  nervous  functions  are  not  restored  until  the  divided 
nerve  fibres  have  gone  through  with  the  process  of  degeneration  and 
regeneration,  and  have  again  acquired  their  natural  continuity  of  text- 
ure. This  shows  that  the  suspension  of  functional  activity  is  directly 
due  to  the  injury  of  the  nerve  fibres,  and  not  to  the  sympathetic  action 
of  other  parts. 

Centripetal  and  Centrifugal  Degeneration  of  divided  Nerve  Fibres. 
— The  degeneration  of  nerve  fibres  in  a  divided  spinal  nerve  (page 
353)  takes  place,  below  the  point  of  section,  throughout  the  peripheral 
portion  of  its  trunk  and  branches,  while  its  central  portion,  above  the 
point  of  section,  remains  unaltered  (Fig.  105,  A).  In  this  peripheral 
degeneration,  all  the  fibres  of  the  nerve,  both  sensitive  and  motor,  are 
involved ;  and  it  is  consequently  plain  that  in  both  kinds  their  separa- 
tion from  the  nervous  centre  has  produced  a  disturbance  of  nutrition 
resulting  in  atrophy.  Such  a  degeneration  is  "  centrifugal ;"  that  is,  it 
affects  the  nerve  fibres  from  the  point  of  section  outward.  This  ex- 
pression does  not  imply  a  gradual  extension  of  the  process  in  that 
direction,  since  we  know  that  in  reality  (page  354)  it  advances  with 
the  same  rapidity  throughout;  but  it  indicates  the  fact  that,  after 
division  of  a  spinal  nerve,  it  degenerates  between  the  point  of  section 
and  the  periphery,  and  not  toward  the  nervous  centre. 

If  the  section  be  made,  not  upon  the  trunk  of  the  nerve,  but  upon 
its  anterior  root  above  its  junction  with  the  posterior  root,  the  same 
result  takes  place  ;  that  is,  the  divided  fibres  degenerate  in  a  centrifugal 
direction,  while  that  portion  of  the  nerve  root  still  connected  with  the 
spinal  cord  remains  unaltered  (Fig.  105,  B).  But  in  this  case  it  is  only 
the  motor  fibres  in  the  nerve  trunk  which  suffer  degeneration ;  its  sensi- 
tive fibres,  derived  from  the  posterior  root,  are  not  affected.  After 
such  a  division,  the  degenerated  motor  fibres  may  be  distinguished,  in 
the  nerve  trunk  and  branches,  from  the  unaltered  sensitive  fibres 
with  which  they  are  associated ;  and  even  after  its  inosculation  with 
other  nerves  and  subsequent  ramification,  the  degenerated  fibres  belong- 
ing to  the  original  nerve  root  may  be  recognized  by  their  microscopic 
appearance.  The  degeneration  or  immunity  of  these  fibres,  therefore, 
depends  on  the  severance  or  the  preservation  of  their  connection  with 
the  spinal  cord. 

But  if  the  section  be  made  on  the  posterior  nerve  root,  between  its 
ganglion  and  the  spinal  cord,  the  effect  is  reversed  (Fig.  105,  C).  In  this 
instance  the  portion  of  nerve  root  attached  to  the  ganglion  remains 
unaltered ;  that  which  is  connected  with  the  cord  suffers  degeneration, 
and  the  degenerated  fibres  can  be  traced  to  their  entrance  into  the  gray 
substance  of  the  posterior  horn.  This  degeneration  is  therefore  "  cen- 
tripetal," since  it  takes  place  between  the  point  of  section  and  the  spinal 


390 


THE    NERVOUS    SYSTEM. 


cord.  The  fibres  of  the  posterior  root  degenerate  wherever  they  are 
separated  from  connection  with  the  ganglion  ;  and  if  the  ganglion 
be  excised,  they  degenerate  in  both  directions  ;  namely,  inward  to  the 
spinal  cord  and  outward  to  the  periphery  (Fig.  105,  D). 


FIG.  105. 


In  <, ITERATION  OF  SPINAL  NERVES  AND  Nr.uvi:  K'.OTS  AFTER  SECTION.— A.  Section  of  Nerve 
Trunk  beyond  the  Ganglion.  B.  Section  of  Anterior  Root.  C.  Section  of  Posterior  Hoot.  D. 
Excision  of  Ganglion,  a.  Anterior  Root ;  p,  Posterior  Root ;  g,  Ganglion. 

These  facts,  first  discovered  by  Waller,*  have  since  been  confirmed  by 
all  observers.  They  show  that  the  nutrition  of  the  anterior  and  poste- 
rior nerve  roots  is  connected  with  different  centres;  since  the  fibres  of 
the  anterior  root  degenerate  when  separated  from  the  gray  substance 
of  the  anterior  horn,  while  those  of  the  posterior  root  degenerate  when 
separated  from  the  spinal  ganglion.  Such  points  are  designated  as 
"  trophic  centres,"  or  centres  of  nutrition  for  the  nerve  fibres  con- 
nected with  them ;  indicating  that  the  fibres  preserve  their  normal 
structure  so  long  as  this  connection  is  retained,  and  degenerate  when 
it  is  cut  off. 

The  nature  of  this  relation  between  nerve  fibres  and  their  centres 
is  unknown.  We  cannot  assume  that  the  nutrition  of  the  fibres  is 
immediately  derived  from  the  cells  of  the  gray  substance  ;  since  although 
the  fibres  of  a  divided  nerve  degenerate  in  the  part  separated  from  its 
centre,  they  are  afterward  regenerated  by  a  process  taking  place,  so 
far  as  we  know,  in  the  nerve  itself  (page  355).  But  it  is  a  relation  of 
great  physiological  importance,  and  extends  to  considerable  tracts  of 
white  substance  in  the  brain  and  spinal  cord. 

Motor  and  Sensitive  Transmission  in  the  Spinal  Cord. — The  sim- 
plest fact  determined,  in  this  respect,  both  by  experimental  research 
and  pathological  observation,  is  that  the  spinal  cord  is  the  exclusive 
or-j-sin  of  communication  between  the  brain,  on  the  one  hand,  and  the 
external  organs  of  sensation  and  motion,  on  the  other ;  since  if  it  be 
divided  by  a  transverse  section,  compressed  by  fractured  bone,  or  dis- 
organized by  disease  at  any  part  of  its  length,  the  result  is  a  complete 
loss  of  sensibility  and  voluntary  motion  below  the  point  of  injury.  The 


*  Coraptes  Remlus  ,U>  1' Academic  des  Sciences.    Paris,  1851,  tome  xxxiii.,  p.  GOG; 
and  1S.YJ,  ti.nu-  xxxiv.,  p.  0:M. 


THE    SPINAL    CORD.  391 

general  nervous  function,  performed  by  the  cord  as  a  whole,  is  there- 
fore completely  demonstrated,  and  is  not  subject  to  any  doubtful  inter- 
pretation. 

But  the  precise  path  followed  by  motor  and  sensitive  impulses  in  the 
spinal  cord  is  much  less  easy  of  determination  than  in  the  nerve  roots. 
The  methods  of  investigation  are  the  same  in  both  instances;  and  are 
intended  to  ascertain,  first ;  What  parts  of  the  spinal  cord  are  sensitive 
or  excitable  under  the  application  of  artificial  stimulus  ?  and  secondly ; 
What  parts  are  the  natural  channels  of  transmission  for  sensation  and 
motion  ?  The  latter  question  is  the  more  important  in  a  purely  physi- 
ological point  of  view ;  but  the  former  is  also  of  consequence  as  a 
guide  in  experimental  research,  and  also  for  the  explanation  of  patho- 
logical phenomena. 

I.  Wliat  parts  of  the  Spinal  Cord  are  sensitive  or  excitable  under 
the  influence  of  artificial  stimulus? 

The  first  portions  of  the  cord  which  present  themselves  after  opening 
the  spinal  canal  are  the  posterior  columns.  The  irritation  of  these 
columns  by  artificial  stimulus,  according  to  all  observers,  produces 
signs  of  sensibility.  This  sensibility  is  most  marked  in  the  immediate 
neighborhood  of  the  posterior  nerve  roots ;  while  at  the  greatest  dis- 
tance from  this  point,  next  the  median  line,  it  may  be  nearly  absent. 
It  is  evident  that  the  sensibility  of  the  posterior  columns  is  largely 
due  to  fibres  of  the  posterior  nerve  roots,  many  of  which  traverse  the 
outer  portion  of  these  columns  in  their  passage  toward  the  posterior 
horns  of  gray  substance.  The  only  discrepancy  on  this  subject  is  in 
regard  to  the  question  whether  the  nerve  roots  are  the  only  sources  of 
sensibility  for  the  posterior  columns,  or  whether  the  longitudinal  fibres 
of  the  columns  have  also  a  sensibility  of  their  own.  Irritation  of  the 
posterior  columns,  like  that  of  sensitive  tracts  generally,  sometimes  pro- 
duces movements  in  various  parts ;  but  these  movements  are  reflex  in 
character,  and  are  the  signs  of  an  irritation  communicated  to  the  ner- 
vous centres. 

Sensibility  also  exists,  according  to  Yulpian,  in  that  portion  of  the 
lateral  columns  contiguous  to  the  posterior  nerve  roots.  But  as  the 
irritation  is  applied  to  points  farther  forward,  the  signs  of  sensibility 
rapidly  diminish,  and  soon  disappear  altogether.  In  all  these  parts,  of 
both  posterior  and  lateral  columns,  the  sensibility  is  most  marked, 
or  even  exclusively  situated,  in  their  superficial  portions ;  and  experi- 
menters are  generally  agreed  that  the  gray  substance  of  the  cord, 
throughout,  is  destitute  of  sensibility  under  the  application  of  artificial 
stimulus. 

Whatever  minor  points,  therefore,  may  remain  in  doubt,  the  principal 
fact  is  unquestioned,  namely,  that  the  posterior  parts  of  the  spinal 
cord,  consisting  of  the  posterior  columns  and  the  adjacent  half  of  the 
lateral  columns,  are  sensitive  to  irritation,  especially  at  their  surface ; 
and  accordingly  inflammation  of  the  meninges,  or  other  diseased  action 
in  this  locality,  may  be  accompanied  by  painful  irritation  of  the  spinal 


392  THE    NERVOUS    SYSTEM. 

cord.  The  irritation  thus  produced  is  still  more  liable  to  cause  pain,  en 
account  of  the  attachment  at  the  surface  of  the  cord  of  the  posterior 
nerve  roots,  which  are  themselves  acutely  sensitive. 

The  properties  shown  by  the  anterior  columns  on  the  application  of 
artificial  stimulus  are,  on  the  whole,  quite  different  from  those  of  the 
posterior  columns.  There  is  some  difference  in  the  results  obtained 
in  this  respect  by  experimenters.  This  difference  mainly  consists  in 
the  fact  that,  according  to  the  large  majority  (Magendie,  Longet, 
Bernard,  Brown-Sequard,  Yulpian,  Flint),  irritation  of  the  anterior 
columns  produces  convulsive  movement  in  the  parts  below ;  while  others 
(Calmeil  and  Chauveau)  have  found  these  columns  inexcitable.  But 
in  such  instances  experiments  with  a  positive  result  are  more  decisive 
than  those  which  are  negative,  since  the  excitability  of  the  anterior 
columns  might  be  suspended  by  opening  the  spinal  cord,  or  by  other 
incidental  conditions ;  but  nothing  of  this  kind  could  confer  upon  them 
a  property  which  they  did  not  naturally  possess. 

There  can  be  no  doubt,  accordingly,  of  the  excitability  of  the  anterior 
columns.  This  excitability,  while  producing  convulsive  movements  in 
the  parts  below,  is  in  most  instances  unaccompanied  by  sensibility. 
The  absence  of  pain,  in  cases  where  the  convulsive  action  is  well 
marked,  has  been  especially  noticed  by  Flint,*  and  is  mentioned  by 
various  other  writers. 

The  sensibility  of  these  parts,  sometimes  observed,  is  slight  in  degree, 
and  is  frequently  suspended  or  abolished  by  exposure  of  the  spinal 
cord. 

The  lateral  columns  are  also  excitable  in  their  anterior  portions,  near 
the  anterior  nerve  roots ;  while  toward  their  posterior  portions,  accord- 
ing to  Yulpian,  the  excitability  diminishes,  and  gradually  gives  place 
to  the  phenomena  of  sensibility  characteristic  of  the  posterior  parts  of 
the  cord. 

The  anterior  and  posterior  portions  of  the  cord  are  therefore  distin- 
guished, in  great  measure,  by  their  mode  of  reaction  toward  external 
irritation.  The  anterior  and  lateral  columns,  on  each  side  of  the  ante- 
rior nerve  roots,  are  excitable,  and  produce  movement  on  being  irri- 
tated ;  and  both  the  posterior  and  lateral  columns,  near  the  entrance  of 
the  posterior  nerve  roots,  are  endowed  with  sensibility.  Inflammatory 
or  other  irritation  of  the  meninges,  over  any  part  of  the  anterior 
aspect  of  the  cord,  may  accordingly  cause  convulsive  movement  in  the 
limbs  below ;  and  either  pain  alone  or  convulsions  alone  may  be  the 
symptoms  of  inflammatory  irritation  of  the  posterior  or  anterior  por- 
tions of  the  cord  respectively.  But  the  morbid  action  most  frequently 
extends  to  both  regions,  and  disturbances  of  sensibility  and  motion  are 
present  at  the  same  time,  or  at  different  periods  in  the  disease. 

II.  What  parts  of  the  Spinal  Cord  are  the  natural  channels  for 
sensation  and  movement  ? 


*  Physiology  of  Man ;  Nervous  System.     New  York,  1872,  p.  276. 


THE    SPINAL    CORD.  393 

This  question  cannot  be  settled  by  applying  an  artificial  stimulus 
to  various  parts  of  the  cord.  Such  experiments  can  only  determine 
the  sensibility  or  excitability  of  a  nervous  tract,  but  not  its  function 
as  a  channel  of  transmission.  A  nervous  tract  might  be  sensitive  to 
external  irritation,  and  yet  the  natural  impulses  of  sensation,  coming 
from  the  periphery,  might  follow  a  different  route.  On  the  other  hand, 
a  part  might  be  capable  of  transmitting  impulses  of  sensation  or  motion, 
received  from  corresponding  nerve  fibres,  and  yet  might  not  itself  be 
either  excitable  or  sensitive.  In  the  peripheral  nerves  and  nerve  roots, 
the  two  sets  of  properties  coexist.  The  posterior  roots,  which  trans- 
mit sensation,  are  themselves  sensitive ;  and  the  anterior  roots,  which 
transmit  the  stimulus  of  motion,  are  excitable.  But  although  these 
properties  are  connected  in  the  nerves  and  nerve  roots,  they  are  not 
necessarily  so  in  the  nervous  centres ;  and  investigation  shows  that 
in  the  spinal  cord  they  are  often  independent  of  each  other. 

The  only  experimental  method  of  ascertaining  the  natural  path,  in 
the  spinal  cord,  for  sensitive  and  motor  impulses  respectively,  is  to 
divide  or  destroy  different  portions  of  the  cord,  and  to  observe  which 
of  these  injuries  is  followed  by  the  loss  or  preservation  of  sensation  or 
movement.  Even  these  experiments  are  not  always  decisive ;  since 
different  parts  of  the  white  and  gray  substance  are  liable  to  influence 
each  other  by  sympathetic  action.  If  division  of  one  column  of  the 
spinal  cord  be  followed  by  loss  of  sensibility,  we  cannot  at  once 
assume  that  the  column  in  question  is  the  organ  of  its  transmission ; 
because  the  loss  of  sensibility  may  be  temporary,  and  due  to  the  shock 
inflicted  upon  neighboring  parts.  The  most  decisive  experiments, 
accordingly,  for  determining  the  channels  of  sensation  and  motion  in 
the  spinal  cord,  are  those  in  which  these  functions  have  remained, 
notwithstanding  the  destruction  of  certain  parts  of  the  cord. 

By  investigating  in  this  way  the  channels  for  sensation  in  the  spinal 
cord,  the  first  fact,  demonstrated  in  such  a  manner  as  to  be  generally 
accepted,  is  that  after  division  of  the  posterior  columns  the  power 
of  sensibility  is  undiminished,  and  the  animal  continues  to  feel  im- 
pressions made  upon  the  integument  of  the  corresponding  parts.  This 
result,  which  was  obtained  by  several  of  the  older  experimenters,  is 
fully  confirmed  by  the  observations  of  Brown-Sequard*  and  Yulpian.f 
The  posterior  columns  therefore  are  not  the  channels  for  ordinary  sen- 
sitive impressions,  notwithstanding  their  own  sensibility  to  artificial 
irritation.  The  converse  of  this  experiment,  namely,  transverse  division 
of  all  parts  of  the  cord  excepting  the  posterior  columns,  as  performed 
by  the  same  observers,  is  followed  by  complete  loss  of  the  power  of 
sensation. 

On  the  other  hand,  if  both  the  anterior  and  lateral  columns  of  white 


*  Physiology  and  Pathology  of  the   Central   Nervous   System.     Philadelphia, 
1860,  p.  19. 
f  Systeme  Nerveux.    Paris,  1866,  p.  373. 


394  THE    NERVOUS    SYSTEM. 

substance  be  divided,  leaving  only  the  posterior  columns  and  the  gray 
substance,  sensibility  remains  ;  and  Brown-Scquard  has  varied  the  mode 
of  procedure  by  dividing  both  anterior,  lateral,  and  posterior  columns 
in  the  same  animal  at  different  levels,  so  that  the  continuity  of  the 
cord  as  a  whole  is  preserved  by  the  gray  substance,  while  all  the  longi- 
tudinal tracts  of  white  substance  are  divided.  In  this  case  sensibility 
remains,  although  diminished  in  intensity. 

The  transmission  of  sensitive  impressions,  therefore,  takes  place 
through  the  gray  substance.  This  substance,  which  is  itself  insensible 
to  direct  irritation,  forms  the  medium  of  communication  between  the 
peripheral  sensitive  nerves  and  the  brain  above.  It  is  not  known 
whether  this  communication  be  made  by  longitudinal  fibres  running 
continuously  through  the  gray  substance,  or  by  successive  connections 
of  the  nerve  cells. 

The  channels  for  voluntary  motion  in  the  spinal  cord  are  mainly  in 
the  posterior  part  of  the  lateral  columns.  These  tracts  have  been  shown 
(page  385)  to  be  continuous  at  the  medulla  oblongata  with  the  anterior 
pyramids  and  their  prolongations  above.  They  are  therefore  known 
as  the  "  pyramidal  tracts ;"  and  they  form  the  medium  of  communica- 
tion between  the  brain  and  the  origin  of  the  motor  nerves  in  the  gray 
substance  of  the  spinal  cord.  This  has  been  established  by  a  variety 
of  investigations,  carried  on  by  different  methods.  It  is  certain,  in  the 
first  place,  that  the  posterior  columns  take  no  direct  part  in  the  act  of 
voluntary  motion,  since  after  their  complete  section  this  power  remains 
unimpaired ;  and  according  to  Brown-Sequard,  if  all  the  rest  of  the  cord 
be  divided,  leaving  the  posterior  columns  untouched,  voluntary  motion 
is  lost  in  the  parts  below.  There  remain  therefore  only  the  lateral 
and  anterior  columns  of  white  substance  which  can  serve  as  tracts  of 
communication  for  voluntary  impulses. 

This  question  has  received  further  elucidation  from  the  study  of 
secondary  degenerations  in  the  spinal  cord,  first  observed  by  Tu'rck* 
in  1851.  These  degenerations  are  similar  to  those  of  the  spinal  nerves 
and  nerve  roots,  when  separated  from  their  trophic  centres.  They  take 
place,  both  in  the  brain  and  spinal  cord,  in  consequence  of  the  destruction, 
by  a  primary  disorder,  of  certain  nerve  centres  or  the  intervening  parts ; 
and  they  are  therefore  known  as  "  secondary  "  degenerations.  They 
extend  for  long  distances  through  the  cerebro-spinal  axis,  involving 
the  tracts  connected  with  the  part  primarily  diseased ;  and  these 
degenerated  tracts  can  then  be  distinguished  from  the  healthy  white 
substance  by  which  they  are  surrounded. 

As  in  the  nerves  and  nerve  roots,  secondary  degenerations  in  the 
spinal  cord,  may  be  ascending  or  descending.  Ascending  degenerations 
are  those  which  extend  from  the  primary  lesion  upward  to  the  brain 
and  are  therefore  centripetal.  Descending  degenerations  extend  from 
the  point  of  lesion  downward  through  the  cord,  and  are  therefore 
centrifugal. 

*  Sitzungsberichte  der  Akademie  der  Wissenchaften.  Wien,  1851,  Band  vi.,  p.  288. 


THE    SPINAL    CORD. 


395 


Destructive  lesions  in  certain  parts 
by  descending  secondary  degenerations, 
through  the  crura  cerebri,  the  anterior 
pyramids,  and  the  posterior  parts  of  the 
lateral  columns  of  the  cord,  that  is  through 
the  entire  length  of  the  pyramidal  tracts. 
Such  a  condition  causes  paralysis  of  volun- 
tary movement,  without  diminishing  the 
power  of  sensibility.  If  the  degeneration  be 
confined  to  one  lateral  half  of  the  spinal 
cord,  paralysis  exists  only  on  that  side ;  if  it 
be  bilateral  both  sides  of  the  body  are  para- 
lyzed. Similar  descending  degenerations 
mayN  take  place  from  any  point  where  a 
lesion  exists  in  the  pyramidal  tracts,  and 
according  to  Charcot  *  these  tracts  may 
also  be  affected  by  a  primary  alteration 
throughout  their  extent  in  the  medulla  ob- 
longata  and  spinal  cord. 

As  the  pyramidal  tracts,  in  descending 
through  the  medulla  oblongata,  reach  the 
decussation  of  the  pyramids,  a  portion  of 
their  fibres  is  continued  upon  the  same 
side  of  the  median  line,  forming  a  narrow 
band  on  the  inner  border  of  the  anterior 
column.  These  bands  are  the  Columns  of 
TurckfFig.  106,  Section  I.).  They  rapidly 
diminish  in  size  from  above  downward, 
and  in  man  come  to  a  termination  in  the 
lower  part  of  the  cervical  region.  The 
greater  part  of  the  pyramidal  tract  crosses 
the  median  line  at  the  decussation  of  the 
pyramids  to  the  opposite  side,  and  is  thence 
traceable  quite  to  the  lower  extremity  of 
the  cord.  In  the  cervical  region  it  occupies 
most  of  the  lateral  columns,  but  in  the 
dorsal  region  is  confined  to  its  posterior 
half,  and  in  the  lumbar  region  is  still  further 
reduced.  Its  fibres  no  doubt  leave  it  at 
successive  points  from  above  downward, 
to  enter  the  gray  substance  of  the  anterior 
horn. 

The  preceding  facts  are  derived  from 
pathological  anatomy.  But  similar  results 


of    the  brain  are  followed 


TRANSVERSE  SECTIONS  OF  THE 
SPINAL  CORD;  showing  degener- 
ation of  the  Pyramidal  Tracts; 
from  a  patient  with  bilateral 
paralysis.  (Charcot.)  I.  Upper 
part  of  Cervical  Enlargement.  II. 
Lower  Cervical  Region.  III.  Dor- 
sal Region.  IV.  Lumbar  En- 
largement. The  degenerated  por- 
tions are  shaded  in  transverse 
lines.  In  Section  I.,  the  Columns 
of  Tiirck  are  visible  at  the  inner 
edge  of  the  anterior  columns. 


*  Lepons  sur  les  Maladies  du  Systeuie  Nerveux.     Paris,  1877,  tome  ii.,  p.  219. 


396 


THE    NERVOUS    SYSTEM. 


have  been  obtained  by  Schiefferdccker  *  in  dogs  after  section  of  the 
spinal  cord  in  the  dorsal  region,  with  consequent  paralysis  of  the  poste- 
rior limbs.  The  degeneration  of  the  pyramidal  tracts  in  these  cases 
was  constant,  and  always  in  a  descending  direction,  from  the  point  of 
section  to  the  lower  extremity  of  the  cord. 

Finally,  in  the  experiments  of  Woroschilofff  on  the  rabbit,  the  func- 
tion of  the  pyramidal  tracts  in  the  lateral  columns  was  investigated 
by  partial  sections  of  the  spinal  cord  in  the  dorsal  region.  The  main 
results  of  these  experiments  are  as  follows : 


PARTIAL  SECTIONS  OF  SPINAL  CORD  OF  RABBIT,  nr  LOWER  DORSAL  REGION.— A,  B?  r.  Without 
Paralysis.  D,  E,  F.  With  Paralysis.  A.  Section  of  Posterior  Columns.  B.  Section  of  Anterior 
and  Posterior  Columns  and  Gray  Substance.  C.  Section  of  Anterior  half  of  Cord.  After  all 
these  sections  the  animal  uses  his  hind  legs  freely  in  locomotion.  D.  Section  of  the  entire  cord 
except  left  lateral  column ;  paralysis  of  right  hind  leg,  preservation  of  motion  in  left.  K.  Section 
of  both  lateral  columns ;  paralysis  of  both  hind  legs.  F.  Section  of  posterior  half  of  cord ;  paralysis 
of  both  hind  legs.  (Woroschiloff.) 

Voluntary  motion  in  the  posterior  limbs  remains  unimpaired  after 
1st,  Section  of  both  posterior  columns  (Fig.  107,  A)  ;  2d,  Section  of  both 
anterior  and  posterior  columns  and  the  gray  substance  (B) ;  and  3d, 
Section  of  the  anterior  half  of  the  cord  on  both  sides  (C).  That  is, 
every  part  of  the  cord,  excepting  the  posterior  half  of  the  lateral  col- 
umns, may  be  divided  in  the  dorsal  region  without  causing  paralysis 
of  the  hind  limbs.  On  the  other  hand  this  paralysis  is  produced  by 
section  of  both  lateral  halves  of  the  cord  outside  the  gray  substance 
(E),  and  by  section  of  the  posterior  half  of  the  cord  on  both  sides  (F) ; 
and  lastly,  division  of  the  whole  cord  excepting  one  lateral  column  (D), 
leaves  the  hind  limb  on  that  side  capable  of  movement  while  the 
opposite  limb  is  paralyzed.  The  transmission  of  voluntary  impulses 
in  the  spinal  cord  takes  place  therefore  through  the  pyramidal  tracts, 

*  Archiv  fur  pathologische  Anatomic  uiul  Physiologic.  Berlin,  1876.  Band 
Ixvii.,  p.  542. 

f  Arbeitcn  aus  der  physiologischen  Anstalt  zu  Leipzig.  Jahrgang,  1874.  Leipzig, 
1875,  p.  99. 


THE    SPINAL    CORD.  397 

occupying  above  the  dorsal  region  the  larger  part  of  the  lateral  columns, 
and  in  the  remainder  of  the  cord  their  posterior  half. 

Similar  experiments  have  been  performed  by  Ott*  on  the  spinal  cord 
of  the  rabbit  in  the  cervical  region,  with  results  essentially  like  those 
above  detailed,  excepting  that  the  effects  of  paralysis  were  exhibited 
in  the  anterior  limbs  as  well  as  the  posterior,  and  that  there  was 
evidence  of  a  certain  amount  of  decussation  of  the  motor  tracts  in  the 
cervical  portion  of  the  cord. 

Descending  degenerations  of  the  pyramidal  tract,  according  to  Charcot, 
do  not  usually  extend  to  the  motor  nerves  or  nerve  roots.  From  this 
it  is  inferred  that  the  pyramidal  fibres  terminate  in  the  gray  substance 
of  the  anterior  horns,  while  the  nerve  roots  consist  of  new  fibres 
originating  from  the  gray  substance.  The  nerve  root  therefore  degen- 
erates only  when  divided  beyond  the  point  of  its  emergence  from  the 
anterior  horn. 

Crossed  Action  of  the  Spinal  Cord. 

The  spinal  cord,  as  a  medium  of  communication  between  the  brain 
and  the  peripheral  organs,  exerts  a  crossed  action.  Sensitive  impres- 
sions received  by  the  integument  on  one  side  of  the  body  are  con- 
ducted through  the  cord  to  the  opposite  side  of  the  brain ;  and  motor 
impulses  originating  on  one  side  of  the  brain  pass  to  the  nerves  and 
muscles  on  the  opposite  side  of  the  body.  This  is  established  both  by 
experiment  on  animals  and  by  pathological  observation  in  man ;  since 
lesions  on  the  right  side  of  the  brain  cause  paralysis,  both  of  sensation 
and  motion,  on  the  left  side  of  the  body,  and  vice  versa.  These  two 
functions  may  be  paralyzed  either  together  or  separately,  according  to 
the  locality  and  extent  of  the  injury  to  the  brain  ;  but  when  the  paraly- 
sis is  distinctly  confined  to  one  side  of  the  body,  the  alteration  of  ner- 
vous tissue  upon  which  it  depends  is  found  after  death  on  the  opposite 
side  of  the  brain. 

Decussation  of  the  Motor  Tracts. — It  may  be  said,  in  general  terms, 
that  the  transmission  of  voluntary  motor  impulses,  in  the  spinal  cord, 
takes  place  continuously  upon  the  same  side.  That  is,  if  a  transverse 
section  of  one  lateral  half  of  the  cord  be  made  at  any  point  in  the 
lumbar,  dorsal,  or  cervical  region,  a  paralysis  of  voluntary  motion  is 
produced  on  the  same  side  for  all  parts  below  the  level  of  the  injury. 
This  observation,  first  made  by  Galen, f  has  been  confirmed  by  all  sub- 
sequent experimenters.  Each  side  of  the  body  therefore  derives  its 
power  of  voluntary  motion  from  the  pyramidal  tract  in  the  corre- 
sponding half  of  the  spinal  cord.  But  at  the  decussation  of  the 
pyramids,  in  the  medulla  oblongata,  these  tracts  cross  to  the  opposite 
side,  afterward  continuing  their  course,  through  the  tuber  annulare  and 
crura  ccrebri,  to  the  brain.  A  lesion  of  the  motor  tract  accordingly 

*  American  Journal  of  the  Medical  Sciences.    Philadelphia,  October,  1879. 
f  De  Locis  Affectis.     Liber  III.,  Cap.  xiv. 


398  TUE  NERVOUS  SYSTEM. 

varies  in  effect  according  to  its  situation.  If  seated  in  the  spinal 
cord,  it  produces  paralysis  on  the  same  side  of  the  body  ;  if  above  the 
decussation  of  the  pyramids,  in  the  medulla,  tuber  annulare,  crus  cere- 
bri,  or  cerebral  hemisphere,  it  produces  paralysis  on  the  opposite  sidr  ; 
and,  finally,  a  lesion  involving  the  decussation  of  the  pyramids  causes 
paralysis  on  both  sides  of  the  body  at  once. 

These  are  the  general  results  of  both  experiment  and  observation, 
and  they  express  the  most  habitual  and  important  conditions  of  uni- 
lateral and  bilateral  paralysis.  But  there  are  certain  variations  from 
the  type  of  simple  and  complete  decussation  which  have  some  influence 
on  the  phenomena. 

First,  the  study  of  descending  degenerations  of  the  pyramidal  tract 
shows  that,  beside  the  principal  mass  of  fibres  in  this  tract  which  cross 
to  the  opposite  side  of  the  cord  at  the  decussation  of  the  pyramids, 
there  are  a  certain  number  which  continue  downward  on  the  same 
side,  forming  in  the  cervical  region  the  ''columns  of  Tiirck "  (Fig. 
106).  These  direct  fibres  are  in  small  proportion,  representing,  on  the 
average,  considerably  less  than  ten  per  cent,  of  the  whole  pyramidal 
tract,  and  in  man  they  do  not  extend,  as  a  rule,  below  the  cervical 
region.  What  becomes  of  them  here  is  unknown ;  but  it  is  evident 
that  their  destination  may  be  twofold.  They  may  terminate  in  the 
anterior  horns  of  gray  substance ;  in  which  case  the  decussation  of  the 
pyramidal  tracts  would  be  partial,  and  the  upper  limb  would  receive 
some  motor  power  from  the  same  side  of  the  brain.  Or  they  may 
finally  cross,  through  the  white  commissure,  to  the  opposite  side  of 
the  cord ;  in  which  case  the  decussation  would  be  complete,  a  part  of 
it  taking  place  below  the  pyramids,  in  the  cervical  region.  This  would 
explain  the  results  obtained  by  various  experimenters  (Van  Kempen, 
Brown-Se'quard,  Vulpian),  who  have  found  that  in  animals  a  division 
of  one  lateral  half  of  the  spinal  cord  in  its  upper  portion  is  followed  by 
a  certain  degree  of  paralysis  on  the  opposite  side.  All,  however,  are 
agreed,  that  this  effect  is  not  produced  by  a  similar  section  in  the  lum- 
bar region,  but  slightly  or  not  at  all  in  the  dorsal  portion,  and  is  only 
pronounced  after  a  section  in  the  cervical  region. 

Secondly,  The  proportion  between  the  direct  and  crossed  fibres  of  the 
pyramidal  tract,  in  man,  may  vary  in  exceptional  cases,  so  that  the 
majority  of  these  fibres  may  be  direct,  and  only  the  minority  decussate, 
Under  these  conditions,  a  lesion  in  the  brain,  contrary  to  the  general 
rule,  would  cause  paralysis  on  the  same  side  of  the  body.  According 
to  Charcot*  such  instances  exist,  although  their  occurrence  is  extremely 
infrequent.  Similar  exceptional  variations  have  been  recorded  in  regard 
to  other  decussating  tracts  in  the  nervous  system. 

Decussation  of  the  Sensitive  Tracts. — Sensitive  impressions,  passing 
from  the  integument  to  the  nervous  centres,  undergo,  like  the  motor 

*  L^ons  sur  les  Localisations  dans  les  Maladies  du  Cerveau  et  do  la  Moelle  t'pi- 
niere.  Deuxieme  Purtie.  Paris,  1880,  p.  195. 


THE    SPINAL    CORD.  399 

impulses,  a  bilateral  dccussation ;  since  lesions  of  the  brain  above  the 
medulla  oblongata  cause  diminution  or  loss  of  sensibility  on  the  oppo- 
site side  of  the  body. 

But  while  the  tracts  for  voluntary  motion  have  a  continuous  unilat- 
eral course  in  the  spinal  cord,  and  decussate  only  or  principally  at  the 
medulla  oblongata,  those  for  sensation  cross  the  median  line  at  succes- 
sive points  throughout  the  length  of  the  cord.  This  is  shown  by  the 
fact  that  a  transverse  section  of  one  lateral  half  of  the  cord,  which 
paralyzes  motion  on  the  same  side,  causes  loss  of  sensibility  on  the 
opposite  side ;  while  the  power  of  sensation  remains  on  the  side  of  the 
injury.  If  a  section  of  one  lateral  half  of  the  spinal  cord  be  made  at 
the  lower  end  of  the  dorsal  region  on  the  right  side,  the  right  hind  leg 
is  paralyzed  of  motion  but  retains  its  sensibility ;  the  left  hind  leg,  at 
the  same  time,  retains  its  power  of  motion  but  loses  its  sensibility. 
Furthermore,  sensibility  is  not  only  retained  on  the  side  of  the  sec- 
tion in  these  cases,  but  is  perceptibly  exaggerated ;  so  that  an  impres- 
sion upon  the  skin  is  perceived  on  that  side  more  acutely  than  before 
the  section. 

These  results,  which  were  partially  obtained  by  several  of  the  older 
experimenters,  wTcre  first  distinctly  brought  out  by  Brown-Sequard. 
According  to  his  experiments,  the  phenomena  are  so  complete  as  to 
imply  an  entire  crossing  of  the  sensitive  tracts  in  the  spinal  cord. 
Other  observers  have  found  the  appearances  less  decisive ;  Yulpian, 
among  others,  maintaining  that  loss  of  sensibility  on  the  opposite  side, 
after  section  of  a  lateral  half  of  the  cord,  is  only  partial,  and  that  sen- 
sitive impressions  conveyed  through  the  gray  matter  may  continue  to 
pass  even  after  one  lateral  half  of  the  cord  has  been  divided  in  the  dor- 
sal, and  the  other  in  the  cervical  region,  by  two  sections  at  a  consider- 
able distance  from  each  other. 

It  is  certain,  however,  that  after  section  of  one  lateral  half  of  the 
cord  the  phenomena  which  indicate  a  crossing  of  the  sensitive  tracts 
are  distinctly  marked.  We  have  found  that  after  such  a  section,  in  the 
dog,  in  the  dorso -lumbar  region,  the  difference  in  sensation  and  motion 
between  the  two  sides  is  very  striking.  Sensibility  is  either  lost  or 
very  much  diminished  on  the  opposite  side,  while  on  the  side  of  the 
section,  there  is  complete  muscular  paralysis  and  increased  sensibility. 

What  causes  the  increase  of  sensibility,  after  section  of  one  lateral 
half  of  the  spinal  cord  ?  It  is  probably  due  to  local  irritation  of  the 
gray  substance  at  the  point  of  section,  producing  in  this  way  an  appa- 
rent exaggeration  of  sensitive  impressions  on  that  side.  For  this  pur- 
pose it  is  not  necessary  to  make  a  complete  section  of  the  lateral  parts 
of  the  cord ;  since  Brown-Sequard  has  found  that  division  of  the  pos- 
terior columns  alone  will  cause  increase  of  sensibility,  more  or  less 
pronounced  in  different  cases ;  and  according  to  Yulpian,  the  same 
effect  may  be  produced  by  simply  pricking  with  a  pointed  instrument 
the  posterior  or  lateral  parts  of  the  cord  on  one  side. 

The  crossing  of  the  sensitive  tracts,  according  to  Brown-Sequard,  is 


400  THE    NERVOUS    SYSTEM. 

especially  demonstrated  by  the  effects  of  a  longitudinal  section  in  the 
median  line.  Such  a  section  in  the  lumbar  region  of  the  cord,  sepa- 
rating at  that  point  its  two  lateral  halves  from  each  other,  is  followed 
by  complete  loss  of  sensibility  in  both  hind  legs.  This  result  alone 
would  not  be  decisive,  since  the  suspension  of  sensibility  might  be 
due  to  the  shock  of  the  operation ;  but  it  is  of  much  value  in  connec- 
tion with  the  fact  that,  although  sensibility  is  lost,  the  power  of  volun- 
tary motion  is  retained  in  both  posterior  limbs. 

Finally,  instances  in  man,  where  a  lesion  of  the  spinal  cord  is  accom- 
panied by  loss  of  voluntary  motion  on  the  same  side  and  loss  of  sensi- 
bility on  the  opposite  side,  confirm  the  results  derived  from  experiment 
on  animals.  The  decussation  of  both  motor  and  sensitive  tracts  is 
complete  in  the  upper  part  of  the  medulla  oblongata ;  but  below  this 
point  the  cord  acts  as  a  conductor  for  motor  impulses  going  to  the 
muscles  on  the  same  side,  and  for  sensitive  impressions  coming  from 
the  integument  of  the  opposite  side. 

Various  forms  of  Paralysis,  from  lesions  of  the  Cerebro-spinal 
Axis. — In  consequence  of  disease  or  injury  in  the  cerebro-spinal  axis, 
a  variety  of  symptoms  may  be  produced  affecting  sensation  and  motion. 
The  principal  forms  of  paralysis  from  this  cause  are,  first,  "  paraplegia," 
or  paralysis  of  the  lower  portion  of  the  body  and  lower  limbs ;  and 
secondly,  "hemiplegia,"  or  paralysis  of  one  lateral  half  of  the  body, 
and  of  one  or  both  limbs  on  the  corresponding  side. 

I.  In  Paraplegia,  the  injury  affects  the  whole  substance  of  the  spinal 
cord  at  a  particular  level,  and  the  result  is  loss  of  sensation  and  volun- 
tary motion  on  both  sides,  for  all  parts  below  the  level  of  the  injury. 
If  the  lesion  occupy  the  lumbar  portion  of  the  cord,  the  legs  and  the 
pelvic  regions  are  paralyzed  and  insensible,  while  the  arms  and  the 
rest  of  the  trunk  are  unaffected.      If  it  be  in  the  dorsal  region,  a 
corresponding  part  of  the  abdomen  and  thorax  is  also  deprived  of 
sense  and  movement ;  and  if  situated  in  the  middle  cervical  region,  it 
produces  paralysis  and  insensibility  of  both  upper  and  lower  limbs,  as 
well  as  of  the  chest  and  intercostal  muscles.     A  paralysis  of  this  kind, 
involving  the  arms  and  the  intercostal  muscles,  is  more  dangerous  than 
that  of  the  legs  alone ;  because  a  slight  extension  of  the  lesion  will 
reach  the  origin  of  the  phrenic  nerves,  and  produce  death  by  stoppage 
of  respiration. 

In  complete  paraplegia,  sensation  and  motion  are  both  abolished  in 
the  affected  parts ;  and  injury  or  disease  in  the  spinal  cord,  when  suffi- 
cient to  destroy  one  of  these  functions,  almost  necessarily  reaches  the 
parts  which  preside  over  the  other.  But  in  slight  or  incomplete  cases, 
either  sensibility  or  movement  may  be  more  or  less  affected,  accord- 
ing to  the  intensity  of  the  lesion  in  different  parts  of  the  cord. 

II.  In  Hemiplegia  of  the  simplest  form,  there  is  loss  of  sensation  and 
voluntary  motion  in  one  upper  and  lower  limb,  and  in  the  integument 
and  muscles  of  the  trunk  on  the  corresponding  side.    It  is,  therefore,  a 
complete  paralysis  of  one  lateral  half  of  the  body ;  the  affection  being 


THE    SPINAL    CORD.  401 

limited  by  the  median  line,  both  in  front  and  rear.  In  such  cases  the 
lesion  is  on  the  opposite  side,  above  the  decussation  of  the  anterior 
pyramids ;  namely,  in  the  upper  part  of  the  medulla  oblongata,  the 
crura  cerebri,  the  cerebral  ganglia,  or  the  hemispheres.  It  is  most 
frequently  seated  in  the  cerebral  ganglia  or  the  hemispheres. 

In  hemiplegia  from  this  cause,  the  loss  of  sensibility  and  the  loss 
of  motion  occupy  the  same  half  of  the  body,  though  they  are  not  always 
equally  well  marked.  When  the  lesion,  on  the  other  hand,  is  in  one 
lateral  half  of  the  spinal  cord,  there  is  loss  of  motion  on  the  corre- 
sponding side  of  the  body,  and  loss  of  sensibility  on  the  opposite  side. 
A  number  of  such  cases  have  been  collected  by  Brown-Sequard,  in 
which  the  situation  of  the  injury  was  ascertained  by  post-mortem 
examination. 

Furthermore,  a  distinction  is  made  between  affections  involving  loss 
of  motion  and  those  accompanied  by  loss  of  sensation.  The  term 
paralysis  indicates  more  especially  an  impairment  or  abolition  of  the 
power  of  voluntary  movement ;  while  diminution  or  loss  of  sensibility 
is  called  anaesthesia.  Either  of  these  affections  may  be  complete  or  par- 
tial ;  confined  to  particular  regions,  or  extending  over  a  considerable 
part  of  the  body.  They  may  be  present  together,  as  in  paraplegia ;  or 
either  may  exist  independently,  as  local  paralysis  or  local  anaesthesia. 
A  loss  of  sensibility  occupying  one  lateral  half  of  the  body  is  known  as 
hemiansesthesia ;  and  as  shown  above,  it  may  be  associated  with  hemi- 
plegia in  the  same  region,  or  the  two  may  coexist  on  opposite  sides. 

The  Spinal  Cord  as  a  Nervous  Centre. 

So  far  as  the  spinal  cord  is  concerned  in  sensation  and  voluntary 
motion,  it  acts  as  a  medium  of  communication  between  the  brain  and 
the  external  parts.  Its  complete  division  at  any  point  destroys  this 
communication ;  so  that  the  commands  of  the  will  are  no  longer  trans- 
mitted to  the  muscles,  and  impressions  made  upon  the  integument  pro- 
duce no  conscious  sensation.  But  after  such  an  operation  motion  is  not 
altogether  abolished  in  the  limbs ;  and  sensitive  impressions,  though 
no  longer  perceived  by  the  individual,  are  still  capable  of  exciting 
muscular  reaction.  These  phenomena,  which  take  place  without  the 
intervention  of  the  brain,  result  from  the  action  of  the  cord  as  a  ner- 
vous centre,  and  are  due  to  the  independent  properties  of  its  gray 
substance. 

Reflex  Action  of  the  Spinal  Cord. — If  a  decapitated  frog  be  allowed 
to  remain  at  rest  for  a  few  moments,  until  the  effects  of  nervous  shock 
have  passed  off,  movement  can  be  excited  in  the  limbs  by  applications 
made  to  the  integument.  If  the  skin  of  one  of  the  feet  be  pinched  with 
forceps,  or  immersed  in  a  weak  acidulated  solution,  the  leg  is  immedi- 
ately drawn  up  toward  the  body,  as  if  to  escape  the  source  of  irrita- 
tion. If  the  stimulus  be  of  slight  intensity,  the  corresponding  leg  only 
will  move ;  but  if  it  be  more  severe,  motion  will  often  be  produced  in 
the  opposite  limb,  or  even  in  all  the  limbs  at  once.  These  phenomena 

2A 


402  THE    NERVOUS    SYSTEM. 

may  be  repeated  a  great  number  of  times,  until  the  irritability  of  the 
nervous  system  is  exhausted,  or  until  some  structural  change  has  taken 
place  in  the  tissues. 

In  the  movements  thus  produced  after  decapitation  there  are  two 
important  peculiarities : 

First,  they  are  never  spontaneous  ;  but  are  excited  only  by  the  appli- 
cation of  an  external  stimulus.  The  decapitated  frog,  if  left  to  itself, 
remains  motionless,  in  a  nearly  natural  attitude,  without  any  tendency 
to  alter  its  position.  Each  application  of  stimulus  causes  a  movement, 
after  which  the  limbs  resume  their  condition  of  quiescence,  until  a  repe- 
tition of  the  stimulus  calls  out  a  new  movement. 

Secondly,  the  action  is  not  produced  by  direct  excitement  of  the  mus- 
cles. The  stimulus  is  applied  to  the  integument  of  the  foot,  and  the 
muscles  of  the  leg  and  thigh  contract  in  consequence.  This  shows 
that  both  sensitive  and  motor  nerves  take  part  in  the  process.  The 
sensitive  fibres  of  the  integument  receive  the  impression  and  convey  it 
inward ;  after  which  the  motor  fibres  transmit  an  outward  stimulus  to 
muscles  in  a  different  part.  Even  other  limbs,  as  already  mentioned, 
may  be  set  in  motion  by  an  irritation  applied  to  the  integument  of  one. 

Furthermore,  the  nervous  action  is  not  transmitted,  in  these  cases, 
directly  from  the  integument  to  the  muscles ;  it  passes  through  the 
spinal  cord,  which  thus  fo'rms  a  link  in  the  chain  of  communication. 
For  if  the  posterior  limb  be  left  uninjured,  while  its  connection  with 
the  cord  is  severed  by  dividing  the  sciatic  nerve  in  the  abdomen,  no 
further  action  can  be  excited,  and  the  limb  remains  motionless  whatever 
irritation  be  applied  to  the  integument. 

Lastly,  if  the  spinal  cord  be  destroyed  by  a  stilet  introduced  into 
the  spinal  canal,  this  also  puts  an  end  to  the  phenomena,  and  irritation 
of  the  integument  will  no  longer  produce  muscular  reaction  in  the  limb. 
The  muscles  can  then  be  excited  only  by  a  stimulus  applied  to  them- 
selves, or  to  their  motor  nerves. 

These  facts  show  that  the  phenomena  in  question  are  due  to  a  reflex 
action,  in  which  three  different  nervous  elements  take  part;  namdv, 
first,  the  sensitive  nerve  fibres,  conveying  an  impression  inward  from 
the  integument;  secondly,  motor  nerve  fibres,  transmitting  a  stimulus 
outward  to  the  muscles ;  and,  thirdly,  a  nervous  centre  between  the 
two,  in  wh'ch  the  reflex  action  is  accomplished.  The  nervous  centre, 
in  this  instance,  is  the  gray  substance  of  the  spinal  cord. 

It  is  evident,  accordingly,  that  consciousness  is  not  necessary  for  the 
reception  of  sensitive  impressions  by  a  nervous  centre ;  and  also  that 
motor  impulses  may  originate  in  a  nervous  centre  without  volition. 
The  reflex  action  of  the  spinal  cord  is  both  unconscious  and  involun- 
tary ;  and  yet  it  is  completely  efficient,  and  produces  muscular  action 
at  once  on  the  application  of  a  stimulus  to  the  skin. 

Diminution  or  Increase  of  Reflex  Action  in  the  Cord. — The  reflex 
action  of  the  spinal  cord,  like  other  forms  of  nervous  activity,  inn y 
suffer  temporary  depression  or  suspension  by  shock  or  injury  to  the 


THE    SPINAL    CORD.  403 

system  at  large.  Decapitation  in  the  frog-  is  often  followed,  for  a  few 
moments,  by  an  interval  of  nervous  paralysis,  in  which  no  phenomena 
of  reaction  can  be  obtained.  Even  injuries  in  which  the  nervous  cen- 
tres are  not  directly  interested,  such  as  opening  the  abdomen  and 
removing  the  abdominal  organs,  may  produce  a  similar  effect.  In  some 
instances  this  period  of  depression  is  very  short,  so  as  to  be  almost 
imperceptible ;  in  others  it  lasts  for  several  minutes.  After  it  has 
passed  off,  the  reflex  irritability  of  the  cord  returns,  and,  if  the  cord 
itself  have  been  wounded  or  divided,  may  even  be  perceptibly  increased 
in  intensity. 

It  is  for  this  reason  that  reflex  action  often  seems  more  vigorous  and 
prompt  in  the  frog  after  removal  of  the  head,  or  after  transverse  division 
of  the  cord  at  its  upper  part.  The  wound  induces  an  increased  excita- 
bility, in  consequence  of  which  sensitive  impressions  produce  a  more 
energetic  reaction.  This  is  shown  by  the  observations  of  Tu'rck,  Ber- 
nard, and  Vulpian,  in  which,  after  section  of  one  lateral  half  of  the  cord, 
the  hind  leg  on  that  side  is  withdrawn  more  rapidly  from  an  acidulated 
solution  than  the  other ;  and  in  which  reflex  action,  in  decapitated 
animals,  becomes  more  marked,  in  consequence  of  successive  transverse 
sections,  in  the  cervical  and  dorsal  regions. 

The  reflex  action  of  the  cord  may  be  increased  by  poisonous  sub- 
stances. Strychnine  is  the  most  efficient  in  this  respect,  and  produces 
an  exalted  irritability  of  the  spinal  cord,  in  consequence  of  which  a 
slight  irritation  of  the  skin  is  followed  by  excessive  muscular  reac- 
tion. In  a  decapitated  frog,  under  ordinary  conditions,  the  reflex  action 
of  the  cord  is  distinct  but  moderate  in  degree.  Slight  irritations  have 
but  little  effect,  and  the  pinching  of  one  hind  foot  usually  causes  retrac- 
tion of  that  limb  only.  But  if  a  solution  of  strychnine  be  injected 
beneath  the  skin,  at  the  end  of  ten  or  fifteen  minutes,  when  absorption 
has  taken  place,  the  reflex  irritability  of  the  cord  is  exaggerated  in  a 
marked  degree.  The  animal  still  remains  motionless  if  undisturbed ; 
but  the  least  irritation  applied  to  the  skin,  such  as  the  contact  of  a  hair 
or  a  feather,  or  the  jar  produced  by  a  blow  upon  the  table  near  by, 
will  often  cause  violent  convulsions,  in  which  all  the  limbs  take  part. 
As  these  effects  arc  produced  in  the  decapitated  animal,  they  are  inde- 
pendent of  the  action  of  the  brain.  Strychnine,  accordingly,  acts  upon 
the  spinal  cord  by  increasing  its  excitability,  thus  causing  convulsive 
movement  from  slight  external  irritation. 

Similar  results  may  follow,  as  a  secondary  consequence,  from  wounds 
or  injuries  either  of  the  spinal  cord  or  of  peripheral  nerves.  Brown- 
Sequard  *  has  shown  that  in  guinea-pigs  a  section  of  one  lateral  half 
of  the  cord  sometimes  produces,  after  a  few  weeks,  such  a  condition 
of  the  nervous  centres  that  epileptiform  convulsions,  of  very  intense 
character,  may  be  excited  by  pinching  the  skin  of  the  face  and  neck,  on 
the  corresponding  side.  The  phenomena  of  tetanus  in  man,  following 

*  Researches  on  Epilepsy.     Boston,  1857. 


404  THE    NERVOUS    SYSTEM. 

wounds  of  peripheral  nerves,  are  also  reflex.  The  tetanic  spasm  is 
usually,  if  not  always,  excited  by  an  external  cause;  and  this  cause 
may  be  so  slight  that  in  the  healthy  condition  it  would  have  no  per- 
ceptible effect.  The  accidental  movement  of  the  bedclothes,  the  shut- 
ting of  a  door,  the  passing  of  a  carriage  in  the  street,  or  even  a  current 
of  air  upon  the  skin,  may  be  sufficient  to  throw  the  muscular  system 
into  spasmodic  action.  The  irritability  of  the  spinal  cord  as  a  nervous 
centre  is,  therefore,  liable  to  be  increased  or  diminished  by  causes  acting 
upon  it  from  without. 

Reflex  Action  of  the  Cord  in  Warm-blooded  Animals  and  in  Man. — 
In  the  frog  and  other  cold-blooded  animals,  the  reflex  action  of  the 
spinal  cord  lasts  for  a  considerable  time  after  death ;  often  continuing, 
if  the  animal  be  kept  in  repose  and  sufficiently  cool  and  moist,  for 
twenty-four  hours  or  longer.  In  the  warm-blooded  animals,  it  disap- 
pears more  rapidly ;  and  it  must  be  sought  for,  if  at  all,  within  a  short 
time  after  death,  since  a  nearly  constant  supply  of  blood  is  essential 
in  these  animals  to  the  irritability  of  the  nervous  system.  But  if  the 
circulation  be  maintained  by  means  of  artificial  respiration,  the  reflex 
action  of  the  cord  will  continue,  independently  of  the  brain ;  and 
although  sensation  and  volition  are  absent,  movements  of  the  leg  may 
be  produced  by  pinching  the  skin  of  the  foot. 

Robin  *  has  observed  the  reflex  action  of  the  spinal  cord,  after  de- 
capitation, in  man,  in  the  case  of  an  executed  criminal  whose  body 
was  subjected  to  examination.  The  muscular  contractions  were  pro- 
duced about  one  hour  after  execution.  "  While  the  right  arm  was 
lying  extended  by  the  side,  with  the  hand  about  25  centimetres  dis- 
tant from  the  upper  part  of  the  thigh,  I  scratched  with  the  point  of  a 
scalpel  the  skin  of  the  chest  at  the  areola  of  the  nipple,  for  a  space 
of  10  or  11  centimetres  in  extent,  without  making  any  pressure  on 
the  subjacent  muscles.  We  immediately  saw  a  rapid  and  successive 
contraction  of  the  great  pectoral  muscle,  the  biceps,  probably  the 
brachialis  anticus,  and  lastly  the  muscles  covering  the  internal  con- 
dyle. 

"  The  result  was  a  movement  by  which  the  whole  arm  was  made  to 
approach  the  trunk,  with  rotation  inward  and  half-flexion  of  the  fore- 
arm upon  the  arm;  a  true  defensive  movement,  which  brought  the  hand 
toward  the  chest  as  far  as  the  pit  of  the  stomach.  Neither  the  thumb, 
which  was  partially  bent  toward  the  palm  of  the  hand,  nor  the  fingers, 
which  were  half  bent  over  the  thumb,  presented  any  movements. 

"The  arm  being  replaced  in  its  former  position,  we  saw  it  again 
execute  a  similar  movement  on  scratching  the  skin,  in  the  same  manner 
as  before,  a  little  below  the  clavicle.  This  experiment  succeeded  four 
times,  but  each  time  the  movement  was  less  extensive;  and  at  last 
scratching  the  skin  over  the  chest  produced  only  contractions  in  the 
great  pectoral  muscle  which  hardly  stirred  the  limb." 

*  Journal  de  1'Anatomie  et  de  la  Physiologic.     Paris,  1869,  p.  90. 


THE    SPINAL    CORD.  405 

The  neck  had  been  severed,  in  the  above  case,  near  the  level  of  the 
fourth  cervical  vertebra. 

Reflex  action  may  also  be  seen,  in  man,  in  certain  cases  of  disease 
of  the  spinal  cord.  If  the  upper  portion  of  the  cord  be  disintegrated 
by  inflammatory  softening,  so  that  its  middle  and  lower  portions  lose 
their  connection  with  the  brain,  paralysis  and  insensibility  ensue  in 
all  parts  below  the  seat  of  the  lesion.  Under  these  conditions,  the 
patient  is  incapable  of  voluntary  motion  in  the  paralyzed  parts,  and 
is  unconscious  of  any  injury  to  the  integument  in  the  same  region. 
But  if  the  soles  of  the  feet  be  gently  irritated  with  a  feather  or  with 
the  point  of  a  needle,  a  convulsive  twitching  of  the  toes  will  often 
take  place,  or  even  retractile  movements  of  the  leg  and  thigh ;  and 
such  movements  may  frequently  be  excited  by  the  sudden  contact  of 
cool  air  with  the  lower  limbs.  We  have  repeatedly  witnessed  these 
phenomena,  in  disease  of  the  spinal  cord,  where  the  paralysis  and 
insensibility  of  the  lower  limbs  were  complete.  Many  similar  instances 
have  been  reported  by  various  authors. 

Physiological  Action  of  the  Spinal  Cord  as  a  Nervous  Centre. — The 
reflex  action  of  the  spinal  cord,  as  it  takes  place  in  the  healthy  condi- 
tion, is  not  easily  brought  under  observation.  In  animals,  unless  the 
head  be  removed  or  the  spinal  cord  separated  from  the  brain,  reflex  and 
voluntary  movements  are  liable  to  be  confounded ;  and  in  man  during 
health,  the  phenomena  of  sensation  and  volition  are  so  prominent  as 
to  obscure  those  which  are  independent  of  the  will.  Nevertheless,  the 
latter  are  exceedingly  important,  and  many  of  them  in  almost  constant 
operation. 

The  general  character  of  reflex  actions  of  the  spinal  cord  is  that 
they  tend  unconsciously  to  the  defence  or  preservation  of  the  body. 
This  is  seen  in  the  simplest  experiments  on  animals.  If  a  decapitated 
frog  be  suspended  in  the  air,  the  posterior  limbs  hang  downward 
in  a  perfectly  relaxed  condition.  On  pinching  one  of  the  feet,  or 
immersing  it  in  acidulated  water,  the  limb  is  retracted  by  its  flexor 
muscles,  the  result  being  a  withdrawal  of  the  foot.  The  muscles 
then  relax,  and  the  limb  lengthens  until  the  foot  touches  the  irritating 
liquid,  when  it  is  again  drawn  up ;  and  so  on,  until  the  irritability  of 
the  cord  is  so  far  diminished  that  it  no  longer  reacts.  In  this  case, 
therefore,  the  only  muscles  thrown  into  activity  are  the  flexors,  which 
tend  to  withdraw  the  foot  from  the  source  of  irritation.  When  an 
irritation  is  applied  to  the  side  of  the  trunk,  it  is  common  to  see  a 
hind  foot  brought  to  the  irritated  spot,  as  if  to  protect  it ;  and  in  some 
instances  the  adaptation  of  reflex  movements  to  accomplish  a  definite 
result  is  very  marked.  This  cannot  be  attributed  to  any  faculty  of 
perception  in  the  spinal  cord ;  since  we  know,  from  pathological  cases 
in  man,  that  when  the  cord  is  separated  from  the  brain  by  disease  or 
injury,  the  parts  below  are  absolutely  deprived  of  sensibility  and  voli- 
tion. The  movement  produced  therefore  depends  simply  on  the  struct- 
ure of  the  limbs  and  the  nervous  mechanism  of  the  spinal  cord.  In 


406  THE    NERVOUS    SYSTEM. 

the  case  of  reflex  action  observed  by  Robin  in  a  decapitated  criminal, 
the  effect  of  irritating  the  skin  over  the  chest  was  a  flexion  and  inward 
rotation  of  the  ami  and  forearm;  and  this  necessarily  brought  the 
lituid  near  the  point  irritated.  It  is  evident  that  the  connection  of 
sensitive  fibres  with  motor  fibres,  through  the  gray  substance  of  the 
cord,  may  be  such  as  to  call  into  action  particular  muscles,  without 
the  intervention  of  consciousness  or  voluntary  impulse.  This  is  the 
character  of  the  reflex  action  of  the  spinal  cord. 

As  a  general  rule,  movements  of  flexion  are  adapted  to  protect  the 
part  from  external  injury,  and  are  excited  by  moderate  causes;  those 
of  extension  are  calculated  to  repel  the  foreign  substance  or  to  escape 
from  it  by  moving  the  whole  body,  and  are  called  out  by  unusual  or 
excessive  stimulus.  The  defensive  character  of  these  movements  is 
frequently  manifest,  in  a  state  of  health,  when  the  brain  takes  no  part 
in  their  production.  If  the  surface  of  the  skin  be  unexpectedly  brought 
in  contact  with  a  heated  body,  the  injured  part  is  often  withdrawn  by 
a  rapid  and  convulsive  movement,  before  we  feel  the  pain,  or  fairly 
understand  the  cause  of  the  involuntary  act.  Whenever  the  body 
accidentally  loses  its  balance,  the  limbs  are  thrown  into  a  flexed  posi- 
tion, calculated  to  protect  the  exposed  parts  and  to  break  the  fall,  by 
a  similar  involuntary  movement.  Notwithstanding,  therefore,  the  evi- 
dent utility  of  these  actions,  they  have  no  intentional  character,  and 
are  performed  without  distinct  consciousness  of  their  object. 

The  spinal  cord  has  also  an  important  action  in  regard  to  attitude 
and  locomotion.  The  preservation  of  the  attitude  alone  requires  the 
harmonious  action  of  many  different  muscles,  all  of  which  contribute  to 
the  position  of  the  body.  This  is  especially  the  case  in  man,  where,  in 
the  standing  posture,  the  body  is  balanced  upon  its  narrow  supports, 
preserving  its  equilibrium  without  attention  or  fatigue.  In  locomotion, 
the  flexors  and  extensors  of  the  limbs  are  associated  in  a  manner  pecu- 
liar to  each  species  of  animal ;  and  in  man  the  balancing  of  the  body, 
in  progression,  requires  a  still  more  extensive  muscular  combination 
than  when  at  rest. 

The  spinal  cord  is  not  sufficient  by  itself  for  the  acts  of  standing 
and  locomotion  ;  since  a  sudden  lesion  which  deeply  injures  the  brain 
or  medulla  oblongata,  or  the  spinal  cord  above  the  cervical  or  lumbar 
enlargements,  at  once  destroys  the  power  of  standing  upright,  or  of 
making  any  effective  movements  of  locomotion.  In  the  frog,  a  very 
natural  attitude  is  often  preserved  after  decapitation,  since  the  body 
rests  by  most  of  its  under  surface  upon  the  ground ;  and  this,  through 
the  reflex  action  of  the  spinal  cord,  brings  the  limbs  underneath  it  in 
a  flexed  position.  If  such  a  frog  be  suspended  in  the  air,  the  limbs 
hung  down  relaxed,  but  resume  the  attitude  of  flexion  when  placed  in 
contact  with  a  hard  surface ;  and,  according  to  Poincarc,*  the  frog  can 
sometimes  be  made  to  execute  a  series  of  leaps,  each  concussion,  as 

*  Leyons  sur  la  Physiologic  <lu  Systfeme  Nerveux.    Paris,  1873,  p.  72. 


THE    SPINAL    CORD.  407 

the  body  strikes  the  ground,  giving  a  fresh  stimulus  for  extension  of 
the  limbs.  But  in  these  animals,  the  muscular  actions  required  for  the 
attitude  and  locomotion  are  very  simple.  In  warm-blooded  quadrupeds 
and  in  man,  on  the  other  hand,  they  are  more  complex,  and  volition  is 
essential  for  either  standing  or  progression.  Both  these  powers  are 
consequently  abolished  by  decapitation. 

But,  although  the  voluntary  impulse  is  necessary  for  the  acts  of  stand- 
ing or  walking,  it  is  not  concerned  in  the  details  of  their  mechanism. 
Once  excited,  the  nervous  action  by  which  walking  is  accomplished 
may  be  kept  up  without  mental  effort  or  attention.  All  we  have  to 
do  is  to  commence  the  process  by  an  act  of  volition,  and  the  requisite 
nervous  machinery  is  set  in  motion.  If  we  decide  to  turn  a  corner,  all 
the  muscular  combinations  necessary  for  that  purpose  are  effected  with- 
out the  intermediate  intervention  of  the  will.  This  secondary  action, 
by  which  motor  impulses  are  combined  in  the  movement  of  the  limbs 
and  trunk,  is  dependent  on  the  action  of  the  spinal  cord. 

The  precise  mode  in  which  this  is  accomplished  is  not  positively 
known.  The  most  probable  explanation  is  that  it  is  due  to  a  constant 
reflex  activity  of  the  cord,  by  which  the  muscles  of  the  body  and  limbs 
are  maintained  in  the  proper  degree  of  tension  or  relaxation ;  and  that 
different  parts  of  the  cord  are  united  with  each  other  for  this  purpose 
by  longitudinal  fibres  in  the  posterior  columns. 

According  to  this  view,  the  fibres  in  question  run  a  comparatively 
short  course  in  the  posterior  columns,  each  one,  after  leaving  the  gray 
substance  at  one  point,  again  entering  it  a  few  centimetres  higher  up ; 
but,  as  they  follow  each  other  in  continuous  series,  they  form  a  mass 
of  connecting  strands  throughout  the  cord.  It  is  certain  that  at  the 
borders  of  the  gray  substance  and  white  columns  of  the  cord  there 
are  fibres  passing  obliquely  from  one  to  the  other ;  and  this  is  espe- 
cially true  of  the  posterior  columns  and  posterior  horns.  It  is  not  pos- 
sible, by  any  means  of  microscopic  investigation  now  in  use,  to  see  the 
origin  and  termination  of  these  fibres ;  but  their  existence  is  rendered 
probable  by  several  well-established  experimental  and  pathological  facts. 

I.  The  posterior  columns  of  the  cord,  as  shown  by  experiment,  are 
not  the  channels  for   either   sensibility  or  voluntary  motion.     But, 
according  to  Vulpian,*  although  a  section  of  these  columns  at  any  one 
point  produces  no  paralysis,  in  the  ordinary  sense,  if  they  be  divided 
by  several  transverse  sections,  two  or  three  centimetres  apart,  there 
is  a  remarkable    disturbance  in  the   power  of  locomotion,  like   that 
which  would  be  due  to  a  want  of  muscular  harmony. 

II.  Destructive  lesions  situated  at  any  point  in  the  spinal  cord  give 
rise  to  secondary  degenerations  like  those  already  described  (page  394), 
which  are  "  ascending"  or  "  descending"  in  various  parts  of  its  lon- 
gitudinal columns.     According  to  Charcot,f  such  secondary  degenera- 

*  Le9ons  sur  la  Physiologie  du  Systerae  Nerveux.     Paris,  1866,  p.  381. 
f  Lefons  sur  les  Localisations  dans  les  Maladies  du  Cerveau  et  de  la  Moelle 
Epiniere.     Deuxieme  Partie.     Paris,  1880,  p.  243. 


408 


THE    NERVOUS    SYSTEM. 


FIG.  108. 


tions  in  the  posterior  columns  are  always  ascending;  that  is,  they 
extend  from  the  primary  lesion  upward  toward  the  brain,  and  never 
in  a  downward  direction.  But  all  parts  of  the  posterior  columns  are 
not  affected  alike.  The  inner  portion  of  these  columns  consists  of  a 
narrow  band,  next  the  median  line,  which  throughout  the  cervical 
region  is  distinctly  divided  from  the  remainder  by  a  narrow  superficial 
furrow.  This  portion  is  known  as  the  funiculus 
gracilis,  or  the  "  column  of  Goll."  At  the  medulla 
oblongata  it  diverges  from  the  median  line,  occupy- 
ing on  each  side  the  inner  border  of  the  restiform 
bodies,  and  forming  the  so-called  "  posterior  pyra- 
mids." These  columns,  in  ascending  degeneration 
of  the  spinal  cord,  are  affected  throughout  their 
length,  above  the  starting-point  of  the  alteration, 
often  quite  to  the  level  of  the  medulla  oblongata 
TRANSVERSE  SECTION  OP  wiv.  108)  ;  and  from  this  it  is  inferred  that  they 

THE  SPINAL  CORD;  show-    v 

ing  ascending  degenera-  consist    mainly   ot    fibres    running    continuously 


FIG.  109 


throughout. 

On  the  other  hand,  in  the  external  portion  of 
the  posterior  column,  or  that  situated  nearest  the  posterior  horn  of 
gray  substance  (Fig.  109),  ascending  degenerations  extend  only  for 
two  or  three  centimetres  above  their  origin.  It  is  therefore  inferred 
that  the  longitudinal  fibres  in  this  part  of  the  column  have  no  great 
length,  and  that  they  originate  successively  from  the  gray  substance, 
to  terminate  in  it  again  soon  afterward  at  a  higher  level. 

III.  Among  the  most  important  facts  bearing  on  this  question  are 
those  connected  with  the  disease  known  as  locomotor  ataxia.  In  this 
affection  there  is  a  remarkable  difficulty  in  walk- 
ing, of  such  a  character  that  the  patient's  natural 
gait  is  altered,  and  he  is  no  longer  sure  of  his 
movements.  He  loses  the  power  of  equilibrium, 
and  cannot  guide  his  foot  to  a  particular  point 
without  a  direct  eifort  of  the  will.  Consequently 
locomotion,  as  usually  performed,  becomes  impos- 
sible; and  yet  the  patient  has  not  lost  in  any 
TRANSVERSE  SECTION  OP  degree  the  power  of  voluntary  movement,  since 

THE      SPINAL     OX>RD;        '  r  J 

showing    sclerosis    of  ne    can    often    exert    his   full   muscular   force   in 
i:it.-rai  portion  of  Poste-  grasping  an  object  or  in  pushing  or  pulling  with 

r  in  r  Columns.    Locomo-  f 

tor  Ataxia.  (Charcot.)  ^ls  tegs  or  arms.  But  he  has  lost  the  power  of 
involuntary  muscular  combination,  which  is  es- 
sential for  ordinary  locomotion.  For  this  reason  the  affection  is  called 
"ataxia,"  and  not  paralysis. 

In  this  disease  the  only  parts  of  the  nervous  system  invariably 
affected  are  the  posterior  columns  of  the  spinal  cord.  They  are  Un- 
seat of  a  structural  degeneration  termed  "  sclerosis,"  in  which  the  con- 
nective tissue  is  increased  in  quantity  mid  density,  while  the  nerve 
fibres  are  altered  and  atrophied.  According  to  Brown-Sequard,  if 


THE    SPINAL    CORD.  409 

limited  to  a  small  extent  of  the  posterior  columns  it  does  not  usually 
affect  the  voluntary  movements;  but  if  it  extend  for  a  distance  of  several 
centimetres,  in  either  the  cervical  or  the  dorso-lumbar  region,  it  always 
causes  a  disturbance  of  these  movements;  and  when  it  occupies  the 
whole  length  and  thickness  of  the  posterior  columns,  the  patient  can 
neither  stand  nor  walk,  although  while  lying  down  and  with  the  aid 
of  vision  he  can  still  move  his  limbs  in  any  direction. 

But  the  sclerosis  of  the  posterior  columns  producing  locomotor 
ataxia  is  confined  to  their  lateral  portions.  In  this  instance  the  disease 
is  not  a  secondary  degeneration,  but  a  primary  alteration  of  structure 
in  the  nervous  tract,  involving  more  or  less  completely  its  various  parts. 
According  to  Charcot,  degeneration  or  sclerosis  of  the  columns  of  Goll 
(Fig.  108)  never  produces  ataxia;  while  sclerosis  of  the  lateral  parts 
of  the  posterior  columns  (Fig.  109)  is  always  accompanied  by  ataxic 
symptoms,  and  these  symptoms  are  more  marked  on  the  right  or  left 
side  or  in  the  upper  or  lower  limbs,  according  to  the  seat  of  the 
structural  alteration. 

These  facts  all  point  to  the  existence  in  the  spinal  cord  of  a  power  of 
reflex  muscular  coordination,  dependent  for  its  exercise  on  the  longi- 
tudinal fibres  of  the  posterior  columns. 

Another  important  action  of  the  spinal  cord,  as  a  nervous  centre,  is 
its  control  over  the  sphincters  and  the  muscles  of  evacuation. 

While  the  small  intestine,  the  caecum,  and  the  colon  are  supplied 
exclusively  with  nerves  from  the  sympathetic  system,  the  lower  portion 
of  the  rectum  receives  branches  from  the  sacral  plexus  of  spinal  nerves, 
distributed  both  to  its  mucous  membrane  and  its  muscular  layer. 
The  lower  part  of  the  lafgs^itestine  is  in  great  measure  a  temporary 
reservoir,  in  which  the  feces  accumulate  until  the  time  arrives  for  their 
evacuation.  The  rectum,  however,  is  in  general  nearly  empty  till 
shortly  before  evacuation ;  and  when  the  feces  begin  to  pass  into  it 
from  above,  it  is  still  capable  of  retaining  them  for  a  certain  period. 
Their  retention  and  discharge  are  provided  for  by  two  sets  of  mus- 
cular fibres ;  namely,  first,  the  sphincter  ani,  which  keeps  the  orifice  of 
the  anus  closed ;  and,  secondly,  the  levator  ani  and  the  circular  fibres 
of  the  rectum,  which  by  their  contraction  open  the  anus  and  expel  the 
feces.  Both  these  acts  are  regulated  by  the  reflex  influence  of  the 
spinal  cord. 

In  the  normal  condition,  the  sphincter  ani  is  habitually  contracted, 
thus  preventing  the  escape  of  the  contents  of  the  intestine.  An  external 
irritation,  applied  to  the  verge  of  the  anus,  causes  increased  contraction 
and  more  complete  occlusion  of  its  orifice.  This  habitual  closure  of 
the  sphincter,  which  is  a  purely  involuntary  act,  as  efficient  during  sleep 
as  in  the  waking  condition,  depends  on  the  reflex  action  of  the  spinal 
cord. 

But  when  the  rectum  has  become  distended  to  a  certain  point,  the 
nervous  action  changes.  The  impression  then  conveyed  to  the  spinal 
cord  causes  relaxation  of  the  sphincter  ani.  At  the  same  time  the 


410  THE    NERVOUS    SYSTEM. 

levator  ani  draws  the  borders  of  the  relaxed  orifice  upward  and  out- 
ward, and  the  feces  are  expelled  by  the  muscular  contraction  of  the 
rectum. 

Both  these  actions  are  in  some  degree  associated,  during-  health,  with 
sensation  and  volition.  The  distention  of  the  rectum  which  precedes 
evacuation  is  accompanied  by  a  sensation,  and  the  resistance  of  the 
sphincter  may  be  intentionally  prolonged  for  a  certain  period.  But  this 
power  of  control  is  limited.  After  a  time  the  involuntary  impulse, 
growing  more  urgent  with  the  increased  distention,  becomes  irresistible; 
and  the  discharge  finally  takes  place  by  reflex  action  of  the  spinal  cord. 

When  the  irritability  of  the  cord  is  exaggerated  by  disease,  its  con- 
nection with  the  brain  remaining  entire,  the  distention  of  the  rectum 
is  announced  by  the  usual  sensation ;  but  the  impulse  of  evacuation  is 
so  urgent  that  it  cannot  be  controlled,  and  must  take  place  at  once. 
The  discharges  are  then  said  to  be  "  involuntary." 

If  the  cord,  on  the  other  hand,  be  disintegrated  in  its  middle  or 
upper  portions,  all  sensibility  and  volition  connected  with  the  action  of 
the  sphincter  are  lost.  The  evacuation  then  takes  place  by  the  ordinary 
mechanism,  as  soon  as  the  rectum  is  filled,  but  without  the  knowledge 
of  the  patient.  The  discharges  are  then  "  involuntary  and  unconscious." 

Finally,  if  the  lower  portion  of  the  cord,  in  an  animal,  be  broken  up 
by  an  instrument  introduced  into  the  spinal  canal,  the  tonic  contraction 
of  the  sphincter  at  once  disappears.  The  same  effect  is  produced,  in 
man,  by  disorganization  of  the  lower  part  of  the  spinal  cord  from  injury 
or  disease.  The  sphincter  ani  is  then  permanently  relaxed,  and  the 
feces  are  evacuated  without  the  knowledge  of  the  patient,  as  fast  as 
they  descend  into  the  rectum  from  the  upper  portions  of  the  intestinal 
canal. 

The  urinary  bladder  serves  also  both  as  a  reservoir  and  an  organ  of 
evacuation,  its  outlet  being  protected  by  the  circular  muscular  fibres 
at  the  commencement  of  the  urethra,  known  as  the  "  sphincter  vesica?." 
While  the  nerves  distributed  to  the  kidneys  are  derived  exclusively 
from  the  sympathetic  system,  those  of  the  bladder  consist  partly  of 
sympathetic  filaments  from  the  mesenteric  ganglia,  and  partly  of  cere- 
bro-spinal  filaments  from  the  lumbar  portion  of  the  spinal  cord,  both 
sets  being  united  in  the  hypogastric  plexus. 

The  tonic  contraction  of  the  vesical  sphincter  during  health,  by  which 
the  urine  is  retained  in  the  bladder,  is  a  continuous,  involuntary,  and 
unconscious  act,  like  that  of  the  sphincter  ani.  At  the  time  of  evacua- 
tion, the  sphincter  is  relaxed  by  a  voluntary  impulse,  and  the  muscular 
coat  of  the  bladder  contracts  to  expel  its  contents ;  but  although  the 
commencement  of  this  process  is  voluntary,  the  subsequent  contrac- 
tion of  the  bladder  continues  independently  of  the  will.  According 
to  the  experiments  of  Giannuzzi*  on  dogs,  irritation  of  the  lumbar 
portion  of  the  spinal  cord,  by  pricking  with  a  steel  needle,  causes  con- 

*  Journal  de  la  Physiologic.     Paris,  1863,  tome  vi.,  p.  22. 


THE    SPINAL    CORD.  411 

traction  of  the  urinary  bladder ;  but  these  contractions  are  no  longer 
produced  after  dividing  the  roots  of  the  sacral  nerves.  Irritation  of 
either  the  sympathetic  or  the  spinal  nerve  filaments  going  to  the  hypo- 
gastric  plexus  produces  contraction  of  the  bladder,  more  energetic  in 
the  latter  case  than  in  the  former. 

Disease  or  injury  of  the  spinal  cord  causing  complete  paraplegia,  is 
usually  accompanied  by  paralysis  of  the  urinary  bladder.  The  muscu- 
lar contraction  of  the  bladder  is  therefore  under  the  influence  both  of 
the  sympathetic  and  cerebro-spinal  systems;  but  its  most  energetic 
stimulus  comes  from  the  spinal  cord  through  the  sacral  nerves. 

The  closure  or  relaxation  of  the  sphincter  vesicae,  on  the  other  hand, 
is  regulated  by  influences  from  the  cerebro-spinal  system  alone.  The 
resistance  of  the  sphincter  to  the  escape  of  fluid  from  the  bladder, 
measured  by  Kupressow,*  in  the  rabbit,  was  found  equal  to  the  press- 
ure of  a  column  of  water  more  than  40  centimetres  in  height.  That 
is,  if  in  this  animal  one  of  the  ureters  were  closed  by  a  ligature,  and 
an  upright  tube  fastened  in  the  other,  the  bladder  and  the  upright 
tube  might  be  filled  with  water  to  a  height,  on  the  average,  of  44  cen- 
timetres without  its  escaping  by  the  urethra ;  beyond  that  point  the 
resistance  of  the  sphincter  was  overcome,  the  water  being  discharged 
by  the  urethral  orifice. 

The  experiments  of  Kupressow  also  show  that  the  nervous  centre 
of  reflex  action  for  the  sphincter  vesicse  is  in  the  lumbar  portion  of  the 
spinal  cord.  If  the  cord  were  divided  at  the  level  of  the  first  or  sec- 
ond lumbar  vertebra,  no  difference  was  perceptible  in  the  resistance  of 
the  sphincter ;  and  sections  at  the  third  and  fourth  lumbar  vertebrae 
diminished  it  by  only  two  centimetres.  But  if  the  cord  were  divided 
at  the  fifth  lumbar  vertebra,  the  resistance  was  reduced  to  14  centi- 
metres ;  and  the  same  effect  was  produced  by  section  at  the  sixth  and 
seventh  vertebrae  of  the  same  region.  The  tonic  contraction,  therefore, 
of  the  sphincter  vesicae,  although  it  may  be  aided  by  volition,  is  directly 
dependent  on  a  nervous  centre  situated,  in  the  rabbit,  about  the  middle 
of  the  lumbar  portion  of  the  spinal  cord  ;  since  it  persists  after  the  cord 
has  been  separated  from  the  brain  by  a  section  at  or  above  the  fourth 
lumbar  vertebra,  but  disappears  after  a  section  at  or  below  the  fifth 
lumbar  vertebra,  thus  destroying  the  nervous  centre  or  cutting  off  its 
communication  with  the  bladder. 

Both  the  retention  of  urine  and  its  evacuation  may  be  accomplished 
without  the  aid  of  volition.  This  is  shown  by  the  experiments  of 
Goltz,f  who  found  that  after  division  of  the  spinal  cord,  in  dogs, 
between  the  dorsal  and  lumbar  regions,  the  animals,  though  deprived 
of  sensibility  and  voluntary  motion  in  the  posterior  limbs,  could  often 
retain  their  urine  for  a  considerable  time,  and  also  evacuate  it  by  a 
regular  and  forcible  contraction  of  the  bladder. 

*  Archiv  fur  die  gesammte  Physiologie.     Bonn,  1872,  Band  v.,  p.  291. 
f  Archiv  fur  die  gesaramte  Physiologie.     Bonn,  1874,  Band  viii.,  p.  474. 


412  THE    NERVOUS    SYSTEM. 

Ill  man,  when  the  sensibility  of  the  bladder  is  exaggerated  by  inflam- 
mation, the  reflex  impulse  to  micturition  is  increased  in  intensity,  pro- 
ducing an  intolerance  of  urine.  Under  these  circumstances  the  urine 
is  discharged  by  a  reflex  act  as  soon  as  it  has  accumulated,  in  small 
quantity,  in  the  bladder.  The  impression  which  excites  this  discharge 
is  accompanied  by  sensation,  but  is  too  urgent  to  be  resisted  by  the 
will. 

On  the  other  hand,  injury  of  the  spinal  cord  in  the  dorsal  region 
may  cut  off  all  sensibility  and  voluntary  power  over  the  bladder,  and 
yet  the  organ  may  be  evacuated  at  regular  intervals  by  the  reflex  aft  ion 
of  the  lumbar  portion  of  the  cord.  But  diseases  or  injuries  which 
affect  the  cord  in  its  lower  portion,  often  produce  complete  paralysis 
of  the  bladder.  The  patient  is  consequently  unable  to  discharge  his 
urine  in  the  ordinary  way,  and  must  be  relieved  by  the  introduction 
of  a  catheter.  If  this  be  not  done,  the  urine  accumulates ;  being 
retained  for  a  time  by  the  elastic  tissues  surrounding  the  neck  of 
the  bladder  and  urethra.  But  after  distention  has  reached  a  certain 
point,  this  resistance  is  overcome ;  and  the  urine  dribbles  away  from 
the  urethra  as  fast  as  it  is  excreted  by  the  kidneys.  Paralysis  of  the 
bladder,  accordingly,  first  causes  distention  of  the  organ,  afterward 
followed  by  a  continuous,  passive,  and  incomplete  discharge  of  its 
contents. 

The  spinal  cord,  in  its  character  as  a  nervous  centre,  exerts  a  general 
protective  influence  over  the  body.  It  presides  over  the  involuntary 
movements  of  the  limbs  and  trunk ;  it  supplies  the  requisite  nervous 
connections  for  the  attitude  and  locomotion ;  and  by  its  control  over 
the  rectum  and  bladder,  it  regulates  the  accumulation  and  discharge 
of  the  excrementitious  products  of  the  system. 


CHAPTER  V. 
THE  BRAIN. 

THE  brain  consists  of  various  deposits  of  gray  substance,  and  of 
tracts  of  white  substance  serving  as  commissures  between  its 
different  regions,  or  as  means  of  communication  with  the  spinal  cord. 
Its  principal  divisions  are  the  cerebral  hemispheres,  the  cerebellum,  the 
tuber  annulare,  and  the  medulla  oblongata.  Of  these  the  hemispheres 
are  by  far  the  largest ;  forming,  in  man,  nearly  four-fifths  of  the  entire 
brain. 

The  Hemispheres. 

The  hemispheres  are  two  ovoidal  masses,  flattened  against  each 
other  at  the  median  line,  where  they  are  separated  by  the  great  longi- 
tudinal fissure,  and  presenting  on  their  lateral  surfaces  a  rounded  or 
hemispherical  form,  whence  their  name  is  derived.  They  consist 
externally  of  a  layer  of  gray  substance  from  two  to  three  millimetres 
in  thickness,  covering  a  mass  of  white  substance,  the  fibres  of  which 
in  general  radiate  from  within  toward  the  cortical  layer.  Their 
surface  is  thrown  into  numerous  convolutions,  separated  from  each 
other  by  fissures  generally  from  10  to  25  millimetres  deep.  These 
fissures,  like  the  great  longitudinal  fissure,  are  the  spaces  where  oppo- 
site surfaces  of  adjacent  convolutions  lie  in  contact  with  each  other ; 
and  they  indicate  the  points  at  which  the  layer  of  gray  substance 
folds  inward,  to  return  upon  itself  again  and  form  the  next  convolu- 
tion. The  larger  quantity  of  gray  substance  is,  therefore,  situated  at 
the  fissures  rather  than  at  the  convolutions ;  and  the  more  numerous 
and  deeper  the  fissures  on  the  surface  of  a  brain,  the  greater  the 
amount  of  gray  substance  which  it  contains. 

Although  the  cerebral  fissures  and  convolutions  are  not  all  the  same 
in  different  brains,  nor  even  exactly  symmetrical  in  the  two  hemispheres, 
yet  many  of  them  are  sufficiently  constant  to  be  regarded  as  essential 
features  of  the  organ  ;  and  the  remainder,  while  varying  within  certain 
limits,  exhibit  a  general  arrangement  characteristic  of  the  species  to 
which  they  belong.  In  man  they  attain  a  very  high  degree  of  devel- 
opment ;  and  their  nomenclature  is  useful  for  designating  different 
parts  of  the  cerebral  surface. 

Next  in  importance  to  the  great  longitudinal  fissure,  which  separates 
the  hemispheres  at  the  median  line,  is  the  Fissure  of  Sylvius  (Fig. 
110,  S).  This  is  a  much  deeper  cleft  than  the  others,  and  exists, 
according  to  Wilder,  in  all  animals  whose  brains  are  fissured  at  all. 
In  man  it  is  the  first  to  appear  during  embryonic  life,  being  visible  as 

413 


414 


THE    NERVOUS    SYSTEM. 


early  as  the  third  month ;  and  in  the  adult  it  forms  a  basis  for  the 
whole  topographical  division  of  the  hemispheres.  It  commences  as  a 
transverse  indentation  on  the  under  surface  of  the  brain,  running 
thence  outward,  backward,  and  upward,  to  form  the  anterior  boundary 

FIG.  110. 


PLAN  OP  THE  HUMAN  BRAIN,  IN  PROFILE;  showing  its  Fissures  and  Convolutions.    S.  Fissure  of 
Sylvius;  S'.  Anterior  Branch ;  S".  Posterior  Branch ;  R.  Fissure  of  Rolando;  P.  Parietal  Fissure. 

of  the  temporal  lobe.  In  some  of  the  inferior  animals  all  the  convolu- 
tions on  the  convexity  of  the  hemispheres  follow  the  course  of  this 
fissure,  bending  round  its  upper  extremity  in  a  loop-like  form ;  and  in 
the  human  brain  a  similar  general  arrangement  is  distinctly  visible. 

On  the  outer  side  of  the  cerebral  hemisphere  the  fissure  of  Sylvius 
presents,  in  man,  two  distinct  branches,  namely,  a  shorter,  anterior 
branch  (S'j,  and  a  longer,  posterior  branch  (S").  At  its  middle  nnd 
anterior  portions,  the  fissure  is  very  deep,  concealing  beneath  its  folds 
a  group  of  short  radiating  convolutions  on  the  lower  and  lateral  surface 
of  the  brain,  called  the  "Island  6Y  Reil,"  or  the  Insula. 

Externally  the  insula  is  covered  by  the  convolutions  included  between 
the  anterior  and  posterior  branches  of  the  fissure  of  Sylvius,  which  pro- 
ject downward  from  above  and  overlap,  at  this  point,  the  deep-sealed 
parts.  This  portion  of  the  cortical  mass  is  known  as  the  "  Opi-ivu- 
lurn,"  or  cover. 

The  second  important  fissure,  on  the  convexity  of  the  hemisphere, 
is  the  Fissure  of  Rolando  (R).  This  fissure  runs  from  near  the  median 
line  outward  and  forward,  reaching  nearly  to  the  fissure  of  Sylvius, 
and  forming  the  boundary  between  the  frontal  and  parietal  portions  of 
the  hemisphere.  It  is  bordered  by  two  convolutions,  running  parallel 
with  itself,  namely,  the  "anterior  and  posterior  central  convolutions." 

The  third  principal  fissure  is  the  Parietal  Fissure  (P).     It  starts 


THE    BRAIN.  415 

from  behind  the  posterior  central  convolution,  and  runs  backward 
through  the  parietal  portion  of  the  hemisphere,  curving  downward 
toward  its  posterior  extremity.  Outside  and  below  it  are  the  arched 
convolutions  about  the  fissure  of  Sylvius ;  inside  and  above  it  is  a  con- 
volution running  parallel  with  the  great  longitudinal  fissure. 

Beside  the  fissures  just  named  there  are  five  others,  which,  though 
less  strongly  marked,  are  constantly  present  and  show  considerable 
regularity  in  their  position  and  arrangement.  The  first  runs  parallel 
with  the  fissure  of  Rolando,  and  a  little  in  front  of  it;  whence  it  is 
called  the  "prseccntral  fissure."  The  second  runs  through  nearly  the 
whole  length  of  the  frontal  lobe,  parallel  in  general  direction  with  the 
great  longitudinal  fissure.  It  divides  the  upper  from  the  middle  portion 
of  the  frontal  lobe,  and  is  called  the  "superior  frontal  fissure."  The 
third  is  the  "  inferior  frontal  fissure,"  and  surrounds  the  end  of  the  short 
anterior  branch  of  the  fissure  of  Sylvius.  The  two  remaining  fissures 
of  this  grade  are  situated  in  the  temporal  lobe,  below  and  behind  the 
fissure  of  Sylvius,  with  which  they  run  in  a  general  parallel  direction. 

The  numerous  remaining  fissures,  which  increase  to  a  great  extent 
the  convoluted  aspect  of  the  cerebral  surface,  are  of  secondary  import- 
ance and  irregular  in  location.  Some  of  them  run  longitudinally  along 
the  middle  of  a  convolution,  dividing  it  into  two  narrower  parallel 
folds  ;  and  some  pass  transversely  between  two  fissures,  across  the  inter- 
vening convolution.  But  if  the  arachnoid  and  pia  mater  be  removed, 
these  secondary  fissures  are  found  to  be  merely  superficial  indentations ; 
not  penetrating,  like  the  others,  deeply  into  the  brain. 

The  principal  convolutions  on  the  convexity  of  the  hemispheres  are 
as  follows : 

The  First  Frontal  Convolution  runs  from  near  the  upper  end  of  the 
fissure  of  Rolando,  forward  along  the  edge  of  the  great  longitudinal 
fissure  to  the  anterior  extremity  of  the  frontal  lobe,  where  it  bends 
downward  and  backward,  terminating  below  in  a  straight  convolution 
next  the  median  line,  resting  upon  the  upper  surface  of  the  orbital  plate. 
This  convolution  is  divided  and  folded  in  many  ways  by  secondary 
transverse,  oblique,  and  longitudinal  fissures,  but  its  general  direction 
is  easily  recognized.  It  is  bounded  externally  by  the  superior  frontal 
fissure. 

The  Second  Frontal  Convolution  runs  parallel  with  the  foregoing 
downward  and  forward  over  the  anterior  and  lateral  part  of  the  frontal 
lobe.  This  is  the  widest  of  the  three  frontal  convolutions,  and  the 
most  abundantly  variegated  by  secondary  folds  and  fissures.  It  is  sepa- 
rated from  the  first  frontal  convolution  by  the  superior  frontal  fissure, 
and  from  the  third  by  the  inferior  frontal  fissure. 

The  Third  Frontal  Convolution  is  situated  at  the  lower  and  outer 
part  of  the  frontal  lobe,  and  curves  round  the  anterior  branch  of  the 
fissure  of  Sylvius.  It  communicates  posteriorly  with  the  lower  end 
of  the  anterior  central  convolution,  and  thus  contributes  to  form  the 
operculum. 


416  THE    NERVOUS    SYSTEM. 

The  Anterior  Central  Convolution  runs  outward  and  forward  from 
the  great  longitudinal  fissure,  along  the  front  edge  of  the  fissure  of 
Rolando.  It  is  usually  a  single  convolution,  but  is  more  or  less  folded 
by  transverse  indentations.  It  communicates  with  the  first  frontal 
convolution  above  and  with  the  third  frontal  convolution  below.  It 
also  curves  round  the  lower  end  of  the  fissure  of  Rolando,  to  unite 
with  the  following  convolution,  which  may  be  considered  as  its  con- 
tinuation. 

The  Posterior  Central  Convolution  is  also  parallel  with  the  fissure 
of  Rolando,  but  behind  it.  Above,  it  turns  backward,  uniting  with 
the  convolutions  of  the  upper  part  of  the  parietal  lobe. 

The  Supra-marginal  Convolution  starts  from  the  lower  part  of  the 
posterior  central  convolution  and  arches  round  the  upper  end  of  the 
fissure  of  Sylvius.  It  then  continues  its  curvilinear  course,  running 
downward  and  forward,  parallel  with  the  inferior  margin  of  the  fissure 
of  Sylvius,  toward  the  end  of  the  temporal  lobe.  In  this  situation  it 
is  known  as  the  First  Temporal  Convolution.  It  is  usually  divided 
throughout  into  two  parallel  convolutions  by  a  secondary  fissure  run- 
ning along  its  axis,  and  both  these  secondary  convolutions  are  more  or 
less  transversely  folded. 

The  Angular  Convolution  originates  from  the  preceding  and  follows 
the  inferior  edge  of  the  parietal  fissure  to  its  posterior  extremity,  where 
it  makes  a  rather  sharp  turn  downward  and  forward,  whence  its  name 
of  the  "angular  convolution."  It  then  becomes  continuous  with  the 
Second  Temporal  Convolution  running  downward  and  forward  in  the 
temporal  lobe.  Below  this  convolution,  and  parallel  with  it,  is  the 
Third  Temporal  Convolution,  forming  the  inferior  border  of  the 
temporal  lobe. 

In  a  horizontal  section  of  the  brain  (Fig.  Ill),  the  convolutions 
are  seen  to  penetrate  its  substance  for  varying  distances  at  different 
regions.  In  the  anterior  and  posterior  parts  they  leave  a  comparatively 
thick  layer  of  white  substance  between  the  cerebral  ganglia  and  the 
gray  matter  of  the  cortex.  But  on  the  side  of  the  brain,  at  the  situ- 
ation of  the  fissure  of  Sylvius,  the  convolutions  reach  to  a  greater 
depth.  The  cerebral  ganglia  are  placed  on  each  side  the  median  line, 
near  the  base  of  the  brain ;  the  anterior  pair,  or  the  corpora  striata, 
being  separated  from  each  other  in  front  by  the  anterior  horns  of  the 
lateral  ventricles  and  the  septum  lucidum,  and  the  posterior  pair,  or  the 
optic  thalami,  being  separated  in  a  similar  manner  by  the  third  ventri- 
cle except  where  they  are  united  by  the  soft  commissure  and  by  the 
peduncles  of  the  pineal  body  and  the  posterior  commissure. 

The  corpora  striata  are  penetrated  from  within  and  below  by  fibres, 
which  run  to  a  great  extent  in  distinct  bundles,  thus  producing  a  visible 
white  striation  in  their  gray  substance.  They  form  on  each  side,  at 
their  anterior  and  lowermost  part,  a  continuous  mass ;  but  through- 
out their  remainder  they  are  divided  by  a  narrow  band  of  white  sub- 
stance into  two  portions,  namely,  the  caudate  nucleus  (6),  so  called 


THE    BRAIN. 


417 


because  it  extends  backward  in  a  slender,  curved,  tail-like  prolonga- 
tion ;  and  the  lenticular  nucleus  (7),  which  has  a  somewhat  lens-like 
figure,  and  is  further  divided  into  three  concentric  zones.  Between 
the  lenticular  nucleus  and  the  optic  thalamus  is  a  band  of  white  sub- 


FIG.  111. 


HORIZONTAL  SECTION  OF  THE  HEMISPHERES,  AT  THE  LEVEL  OF  THE  CEREBRAL  GANGLIA.— 1.  Great 
longitudinal  Fissure,  between  frontal  lobes;  2.  Great  longitudinal  Fissure,  between  occipital 
lobes;  3.  Anterior  part  of  Corpus  Callosum  ;  4.  Fissure  of  Sylvius ;  5.  Convolutions  of  the  Insula; 
6.  Caudate  Nucleus  of  Corpus  Striatura;  7.  Lenticular  Nucleus  of  Corpus  Striatum;  8.  Optic 
Thalarnus;  9.  Internal  Capsule;  10.  External  Capsule;  11.  Claustrum. 

stance,  the  internal  capsule  (9),  consisting  of  fibrous  bundles,  the  con- 
tinuations of  the  crura  cerebi,  passing  obliquely  upward  and  outward 
from  below.  The  optic  thalamus  (8),  situated  on  the  inner  side  of 
the  internal  capsule  is  of  a  lighter  and  more  uniform  tint  than  the 
corpus  striatum,  since  the  nerve  fibres  which  penetrate  it  from 
below  are  dispersed  in  minute  brush-like  ramifications  through  its 
substance.  On  the  outer  aspect  of  the  lenticular  nucleus  is  a  second 
envelope  of  white  substance,  known  as  the  external  capsule  (30), 
with  a  thin  layer  of  gray  substance,  the  claustrum,  or  partition  (11), 
and  beyond  that  the  white  substance  and  convolutions  of  the  insula 

2B 


418 


THE    NERVOUS    SYSTEM. 


FIG.  1 1 2. 


B  9    ' 

Efl 


\  IK  I  KM.  SKCTK.V  OF  ONE  OF  THE  CKRKBRA1   COH- 

voi.r'i  i"N>  :  ^li»\\inur  pyramidal  cells,  and  han- 
dles of  liliri's  pa^iii-  oiit\var<l  frutii  tin'  \vliiU; 
substance.  Magnified  300  diaim  t«-i>.  Ilmle.) 


(5).  At  this  situation,  accord- 
ingly, the  gray  substance  of  the 
cortex  is  in  close  proximity  to 
that  of  the  cerebral  ganglia,  while 
elsewhere  it  is  separated  from 
them  by  a  considerable  thickness 
of  white  substance. 

Gray  Substance  of  the  Convo- 
lutions.— The  gray  substance  on 
the  surface  of  the  hemispheres 
forms  a  convoluted  layer,  into 
which  the  nerve  fibres  penetrate 
from  the  central  mass  of  white 
substance.  It  consists  of  a  uni- 
formly granular  matrix,  in  which 
are  imbedded  nerve  cells  and  their 
prolongations,  together  with  the 
nerve  fibres  dispersed  among 
them.  It  is  divided  into  several 
superimposed  layers,  distinguish- 
ed by  the  form,  size,  and  numbers 
of  the  nerve  cells  which  they 
contain.  The  most  characteristic 
of  these  elements  are  the  so- 
called  "pyramidal  cells,"  occupy- 
ing the  middle  portion  of  the  gray 
substance.  They  have  a  pointed 
extremity,  directed  outward, 
while  the  base  looks  toward  the 
white  substance  of  the  interior. 
The  most  superficial  of  these  cells 
are  the  smallest  and  most  numer- 
ous, averaging  about  10  mmm.  in 
diameter.  Those  which  are  more 
deeply  seated  are  less  abundant, 
but  of  larger  size,  from  25  to 
40  mmm.  in  diameter.  Some  of 
the  prolongations  from  the  base 
of  the  cells  lose  themselves 
in  the  bundles  of  nerve  fibres 
entering  from  the  white  sub- 
stance. 

Beneath  the  pyramidal  cells  is 
a  layer  containing  much  smaller 
cellular  elements,  from  8  to  10 
mmm.  in  diameter,  known  as  the 
''nuclear  layer."  Its  cells  have 


THE    BRAIN.  419 

fine  diverging  processes,  whose  termination  and  connections  are  un- 
known. 

As  the  bundles  of  nerve  fibres  penetrate  the  gray  substance,  they 
rapidly  diminish  in  size,  their  fibres  diverging  laterally  to  pursue  a  more 
or  less  horizontal  course ;  and  in  the  external  portions  of  the  gray  sub- 
stance there  are  only  isolated  fibres  running  in  various  directions. 
During  this  dispersion,  the  nerve  fibres  become  reduced  to  their  smallest 
dimensions,  measuring,  according  to  Kolliker,  from  1  to  2  mmm.  in  diam- 
eter. Most  of  them  spread  out  at  various  levels  in  the  gray  substance, 
while  others  reach  quite  to  its  superficial  portions. 

Structure  of  the  Gray  Substance  in  Special  Parts  of  the  Hemi- 
spheres.— The  gray  substance  of  the  convolutions  presents  certain 
peculiarities  in  particular  regions,  the  most  important  of  which  are 
those  described  by  Betz.*  These  observations,  which  were  based  on 
the  examination  of  more  than  one  thousand  sections,  show  that  there 
are  differences  of  structure  in  the  gray  substance  characteristic  of  ex- 
tensive portions  of  the  hemispheres.  The  cerebral  surface  is  divided, 
in  this  respect,  by  the  fissure  of  Rolando  into  two  main  departments, 
an  anterior  and  a  posterior.  The  anterior  department,  including  the 
convexity  of  the  frontal  lobe,  its  under  surface  resting  on  the  orbital 
plate,  and  its  median  surface  at  the  great  longitudinal  fissure,  is  distin- 
guished by  the  preponderance,  in  its  gray  substance,  of  the  layer  of 
pyramidal  cells.  In  the  posterior  department,  on  the  other  hand,  in- 
cluding both  the  occipital  and  temporal  lobes,  the  nuclear  layer  pre- 
dominates, the  pyramidal  cells  being  less  abundant. 

Furthermore,  at  the  posterior  border  of  each  of  these  two  depart- 
ments there  is  a  special  region,  characterized  by  cells  of  a  particular 
variety.  In  front  is  the  region  of  the  so-called  giant  pyramidal  cells. 
It  occupies  the  whole  of  the  anterior  central  convolution  and  the  upper 
end  of  the  posterior  central  convolution,  and  extends  into  the  "para- 
central  lobule,"  which  is  a  continuation  of  these  two  convolutions  on 
the  median  surface  of  the  hemisphere.  The  pyramidal  cells  in  this 
region,  as  their  name  implies,  are  the  largest  in  the  brain,  approxi- 
mating and  often  equalling  in  size  those  of  the  anterior  horns  of  gray 
substance  in  the  spinal  cord.  They  are  from  40  to  60  mmm.  in  width, 
and  from  50  to  120  mmm.  in  length.  They  all  have  a  number  of 
radiating  processes,  among  which  are  two  principal  ones.  One  of  them, 
given  off  from  the  point  of  the  pyramidal  cell,  runs  in  a  tapering  and 
branching  form  toward  the  external  surface  of  the  convolution.  The 
other,  which  is  given  off  from  the  base  of  the  cell  and  runs  inward 
toward  the  white  substance,  is  slender  at  its  commencement,  but  soon 
grows  thicker  and  acquires  a  medullary  layer,  assuming  the  appearance 
of  a  nerve  fibre. 

The  posterior  special  region  occupies  the  extremity  of  the  occipital 
lobe.  Its  characteristic  cells  are  of  rather  large  size,  but  have  few 

*  Centralblatt  fur  die  medicinische  Wissenschaften.     Berlin,  1874.     Nos.  37  and  38. 


420  THE    NERVOUS    SYSTEM. 

processes  and  no  distinctly  marked  axis  cylinder  prolongation.  Their 
terminal  process  is  very  slender  and  without  lateral  branches  ;  while 
their  basal  processes  extend  mainly  in  a  horizontal  direction,  and  some- 
times communicate  with  those  of  adjacent  cells.  These  observations 
have  been  confirmed  in  many  particulars  by  Tuke,*  Lewis,f  and  Char- 
cot,;};  and  are  generally  accepted  by  cerebral  anatomists. 

Course  of  Fibres  in  the  White  Substance  of  the  Hemispheres.  —  The 
white  substance  of  the  hemispheres  consists  mainly  of  nerve  fibres  or 
fibrous  tracts  belonging  to  three  different  orders,  namely  :  1st.  Com- 
missural  fibres  ;  2d.  Fibres  of  association  ;  and  3d.  Medullary  fibres. 

I.  The  commissural  fibres  are  those  which  connect  with  each  other 
similar  parts  of  the  right  and  left  hemispheres.     Their  principal  mass 
is  in  the  "corpus  callosum,"  or  great  transverse  commissure  of  the 
cerebrum,  which  forms  a  broad  band  of  white  substance  at  the  bottom 
of  the  longitudinal  fissure  and  from  which  the  constituent  fibres  spread 
out  on  each  side  to  all  the  convolutions  of  the  frontal  and  occipital 
lobes,  and  to  the  upper  and  posterior  portions  of  the  temporal  lobe. 
Next  in  importance  is  the  "  anterior  commissure,"  a  narrow  cylindrical 
band  of  white  substance  crossing  the  median  line  near  the  base  of  the 
brain,  a  little  in  front  of  the  optic  thalami,  and  whose  fibres  radiate  on 
each  side  to  the  lower  and  anterior  parts  of  the  temporal  lobe.     This 
is  accordingly  a  special  transverse  commissure  for  the  convolutions 
situated  below  the  fissure  of  Sylvius,  while  the  corpus  callosum  is  a 
general  transverse  commissure  for  those  situated  above,  in  front  and 
behind  it.     By  these  commissural  fibres  the  convolutions  of  each  region 
of  the  hemisphere  are  placed  in  connection  with  those  of  the  corre- 
sponding region  on  the  opposite  side. 

II.  The  fibres  of  association  form  tracts  lying  immediately  beneath 
the  gray  substance  running  in  a  general  longitudinal  direction,  and 
connecting  different  convolutions  on  the  same  side.     Many  of  them 
have  a  short  course,  connecting  the  gray  substance  of  adjacent  convo- 
lutions ;  others  are  longer,  passing  beneath  one,  two,  or  even  three 
intermediate  convolutions  ;  while  others  run  a  very  extended  course, 
as  from  the  point  of  the  frontal  lobe,  along  the  edge  of  the  longitudinal 
fissure  to  the  end  of  the  occipital  lobe,  or  following  the  borders  of  the 
fissure  of  Sylvius  to  the  end  of  the  temporal  lobe.     According  to 
Huguenin,  it  must  be  admitted  that,  in  general,  all  the  principal  con- 
volutions of  a  cerebral  hemisphere  are  connected  with  each  other  by 
fibres  of  association,  in  longer  or  shorter  tracts. 

III.  The  medullary  fibres  are  those  which  connect  the  hemispheres 
with  the  medulla  oblongata.     They  come  up  from  the  spinal  cord, 
through  the  medulla  oblongata,  and  emerge  from  the  superior  border 
of  the  tuber  annulare,  as  the  crura  cerebri.     The  crura  cerebri  are 
divided,  about  the  middle  of  their  thickness  by  a  thin  blackish 


*  Edinburgh  Medical  Journal,  1875,  vol.  xx.,  p.  394. 

f  Brain.     London,  1878,  p.  79. 

J  Li'v»ns  *ur  k-s  Localisations  dans  les  Maladies  du  Cerveau.     Paris,  1878,  p.  34. 


THE    BRAIN.  421 

lamina,  into  two  parts,  a  superior  and  an  inferior.  The  inferior  part, 
or  that  visible  on  the  under  surface  of  the  brain,  is  called  the  "  base  " 
of  the  crura  cerebri.  It  consists  of  two  conspicuous  diverging  bundles, 
the  fibres  of  which  go  to  the  corpora  striata  and  internal  capsule.  The 
superior,  deep-seated  portion  of  the  crura  cerebri  is  called  the  "teg- 
mentum  "  or  cap.  Its  fibres  pass  to  the  optic  thalami  and  internal 
capsule. 

The  internal  capsule  accordingly  represents,  on  each  side,  the  con- 
tinuation of  the  crus  cerebri.  But  this  continuity  is  an  interrupted 
one.  The  fibres  forming  the  crus  cerebri  plunge,  for  the  most  part, 
directly  into  the  corpus  striatum  in  front  and  the  optic  thalamus 
behind,  becoming  dispersed  in  the  gray  substance  of  these  ganglia,  and, 
to  all  appearance,  terminating  in  or  among  their  nerve  cells.  These 
fibres,  at  the  same  time,  are  replaced  by  others  which  originate  in  the 
cerebral  ganglia,  and  which,  passing  obliquely  upward  and  outward, 
join  the  internal  capsule,  to  continue  their  course  toward  the  gray  sub- 
stance of  the  hemispheres.  At  the  upper  border  of  the  ganglia,  they 
spread  out  in  the  diverging  bundles  of  the  corona  radiata,  and  thus 
reach,  at  last,  the  convolutions  of  the  cortex.  The  internal  capsule  is 
accordingly  composed  partly  of  fibres  which  come  up  from  the  crura 
cerebri,  and  terminate  in  the  cerebral  ganglia,  and  partly  of  fibres 
which  start  from  the  ganglia,  and  run  upward  to  the  cortex ;  and  the 
communication  between  the  cerebral  convolutions  and  the  spinal  cord 
is,  for  the  greater  part,  an  indirect  communication  through  the  cerebral 
ganglia. 

Direct  Medullary  Fibres. — Beside  the  fibres  above  described,  there 
is  evidence  that  the  internal  capsule  contains  also  tracts  of  direct  com- 
munication, which  pass  through  it  from  the  convolutions  to  the  crura 
cerebri  without  interruption  by  the  gray  substance  of  the  ganglia. 
These  direct  fibres  are  of  two  kinds,  namely  ;  first,  motor  fibres,  passing 
from  the  convolutions  about  the  fissure  of  Rolando,  through  the  middle 
part  of  the  crura  cerebri,  to  the  pyramidal  tracts  of  the  spinal  cord ; 
and,  secondly,  sensitive  fibres,  passing  from  the  spinal  cord  along  the 
outer  border  of  the  crura  cerebri,  through  the  posterior  part  of  the 
internal  capsule  toward  the  convolutions  of  the  occipital  lobe. 

I.  The  direct  motor  fibres  of  the  internal  capsule  have  not  been 
clearly  demonstrated  by  methods  of  dissection ;  the  intricate  crossing 
in  the  upper  part  of  the  capsule  making  it  difficult  to  follow  individual 
fibres  for  a  sufficient  distance.  Their  existence  is  mainly  inferred  from 
the  occurrence  of  descending  degenerations  in  this  part  of  the  brain. 
According  to  Charcot,*  destructive  lesions  of  the  cortical  substance, 
in  the  anterior  and  posterior  central  convolutions,  give  rise  to  descend- 
ing degenerations  which  pass  through  the  internal  capsule,  crura 
cerebri,  anterior  pyramids,  and  lateral  columns  of  the  cord.  Such 


*  Le9ons  sur  les  Localisations  dans  les  Maladies  du  Cerveau.     Paris,  1878,  pp. 
156,  166. 


422  THE    NERVOUS    SYSTEM. 

descending-  degenerations  take  place  without  any  accompanying  lesion 
of  the  cerebral  ganglia,  and  they  are  not  produced  by  similar  morbid 
alterations  of  the  cortex  in  other  parts  of  the  brain.  Instances  of  this 
kind,  observed  during  a  period  of  fifteen  years,  point  to  an  immediate 
connection  of  certain  fibres  of  the  crus  cerebri  and  internal  capsule  with 
the  central  convolutions  of  the  cerebral  hemispheres. 

2d.  The  direct  occipital  fibres  of  the  crus  cerebri  constitute  a  distinct 
tract  on  its  external  border,  which  turns  outward  beneath  the  extremity 
of  the  optic  thalamus,  and,  forming  the  posterior  part  of  the  internal 
capsule,  curves  backward  toward  the  occipital  convolutions.  This 
tract,  which  was  described  by  Gratiolet,*  from  the  dissection  of  brains 
hardened  in  alcohol,  has  been  recognized  by  Meynert  and  Huguenin, 
and  is  generally  admitted  on  anatomical  grounds.  Its  existence,  as 
well  as  the  sensitive  character  of  its  fibres,  is  furthermore  indicated  by 
the  fact  that  destructive  injuries  of  the  posterior  part  of  the  internal 
capsule,  in  which  it  is  situated,  produce  loss  of  sensibility  on  the  oppo- 
site side  of  the  body. 

Physiological  Properties  and  Function  of  the  Hemispheres. — The 
most  important  function  belonging  to  the  hemispheres,  as  a  whole,  is  no 
doubt  connected  with  the  exercise  of  the  intelligence.  It  is  this  part 
of  the  brain  which  is  most  developed  in  man  as  compared  with  the 
lower  animals ;  and  of  all  the  nervous  endowments  it  is  the  intellectual 
faculties  in  which  he  is  most  distinctly  their  superior.  There  are 
furthermore  a  number  of  special  considerations  which  show  that  the 
cerebral  hemispheres  are  in  some  way  the  especial  organ  of  the  mind. 

I.  It  is  certain  in  the  first  place  that  the  hemispheres  are  not  directly 
connected  with  the  maintenance  of  physical  life,  and  are  not,  even  in 
man,  essential  to  its  continuance.  They  may  be  completely  removed, 
on  both  sides,  in  fishes,  reptiles,  birds,  and  even  in  some  mammalians, 
as  the  rabbit  and  the  rat;  and  in  the  higher  quadrupeds  large  portions 
of  their  substance  may  be  destroyed,  leaving  all  the  vital  functions  in 
continued  activity.  In  man  they  may  suffer  extensive  morbid  altera- 
tions or  mechanical  injuries,  accompanied  by  loss  of  substance,  without 
fatal  result.  One  of  the  most  marked  instances  of  this  kind  is  that 
reported  by  Bigelow,f  in  which  a  pointed  iron  bar,  over  one  inch  in 
thickness,  was  driven  through  a  man's  head  by  the  premature  blasting 
of  a  rock.  The  bar  entered  the  left  side  of  the  face  near  the  angle  of 
the  jaw,  and  passed  obliquely  upward,  inside  the  zygomatic  arch  and 
through  the  anterior  part  of  the  cranial  cavity,  emerging  from  the 
frontal  bone  at  the  median  line,  just  in  front  of  the  union  of  the  coro- 
nal and  sagittal  sutures.  The  patient  became  delirious  within  two 
days  after  the  accident,  remaining  partly  delirious  and  partly  comatose 
for  about  three  weeks.  He  then  beg'an  to  improve,  and  at  the  end  of 
rather  more  than  two  months  from  the  date  of  the  injury  was  able  to 

*  Anatomie  Cornpar£e  dn  SysteTne  Nerveux.     Paris,  1857,  p.  186. 

f  American  Journal  of  the  Medical  Sciences.     Philadelphia,  July,  1  >•'»(>. 


THE    BRAIN.  423 

walk.  At  the  end  of  sixteen  months  the  wounds  were  healed,  and  the 
patient  had  recovered  his  general  healtn,  though  with  loss  of  sight  in 
the  eye  of  the  injured  side.  He  survived  for  a  little  over  twelve  years, 
being  able  to  do  the  work  of  an  ostler,  coachman,  and  farm-laborer,  in 
all  of  which  occupations  he  was  employed  at  various  intervals.  The 
skull,  deposited  in  the  Warren  Anatomical  Museum,*  shows  the  points 
of  entrance  and  exit  of  the  bar. 

Other  cases  of  severe  injury  to  the  hemispheres,  which  have  been 
recorded  from  time  to  time,  show  that  they  do  not  take  an  important 
part  in  the  immediate  functions  of  life. 

II.  The  results  derived  from  comparative  anatomy,  and  from  extir- 
pation of  the  hemispheres  in  animals,  indicate  that  these  organs  are 
especially  connected  with  the  manifestations  of  conscious  intelligence, 
as  distinguished  from  involuntary,  reflex,  or  instinctive  actions.  So 
far  as  we  can  appreciate  the  signs  of  intelligence  in  different  species, 
they  correspond  in  development  with  the  hemispheres,  rather  than  with 
any  other  portion  of  the  encephalon.  In  many  animals,  muscular  power 
and  endurance,  the  activity  of  the  special  senses,  and  the  promptitude 
of  the  instincts,  are  greater  than  in  man ;  while  in  man,  the  intelli- 
gence is  invariably  superior  to  that  of  animals,  and  consequently  gives 
him  the  advantage  over  them.  Even  among  animals,  that  which  espe- 
cially characterizes  certain  species,  and  which  most  nearly  resembles 
that  of  man,  is  a  teachable  intelligence  ;  that  is,  one  which  understands 
the  meaning  of  impressions  received  from  the  exterior,  and  thus  enables 
its  possessor,  through  the  acquisition  of  new  ideas,  to  profit  by  ex- 
perience. 

After  complete  removal  of  the  hemispheres,  in  animals  where  this 
operation  can  be  performed  without  danger  to  life,  the  general  result 
is  the  loss  of  spontaneous  action,  and  of  the  conscious  adaptation  of 
movements  to  external  conditions ;  while  the  ability  to  perform  instinc- 
tive and  reflex  movements  is  retained.  In  the  pigeon,  the  standing 
posture  is  maintained  without  difficulty.  The  bird  can  usually  rest 
with  security  upon  a  perch,  and  when  forcibly  dislodged  will  fly  for  a 
short  distance  and  alight  upon  the  ground  in  a  nearly  natural  manner. 
But  while  undisturbed  he  remains  in  a  state  of  profound  quietude,  with 
his  eyes  closed,  and  indifferent  to  surrounding  objects.  There  is  no 
spontaneous  exercise  of  volition,  but  only  such  acts  as  are  excited  by 
the  impressions  of  the  moment.  Occasionally  he  opens  his  eyes, 
stretches  his  neck,  shakes  his  bill  once  or  twice,  or  smooths  the 
feathers  upon  his  shoulders,  immediately  relapsing  into  his  former 
condition  of  apathy. 

But  there  are  still  indications  of  both  general  and  special  sensibility. 
If  the  foot  be  pinched  with  a  pair  of  forceps,  the  bird  becomes  par- 
tially roused  and  moves  once  or  twice  from  side  to  side.  Yulpian 
has  seen  a  pigeon  within  a  short  time  after  the  operation  shake  the 

*  Descriptive  Catalogue  of  the  Warren  Anatomical  Museum.    Boston,  1870,  p.  145. 


424  THE    NERVOUS    SYSTEM. 

head  briskly  in  consequence  of  a  fly  having  alighted  on  the  wound. 
The  discharge  of  a  pistol  behind  his  back  will  often  cause  him  to  open 
his  eyes  and  turn  his  head,  as  if  in  sign  of  having  heard  the  report ; 
but  he  immediately  becomes  quiet  again  and  pays  it  no  further  atten- 
tion. Vulpian  found  that  in  a  pigeon,  after  the  animal  had  been 
roused  by  pinching  the  foot,  the  sudden  approach  of  a  hand  toward 
the  eye  caused  a  winking  movement  with  partial  turning  of  the  head. 
Sometimes  such  a  pigeon  will  fix  his  eye  on  a  particular  object  for 
several  seconds  together ;  and  Longet  found  that  on  moving  a  lighted 
candle  before  the  bird  in  a  dark  place,  its  head  would  often  follow  the 
movements,  showing  that  the  retina  was  still  sensitive  to  light. 

But  it  is  doubtful  whether  such  movements  indicate  a  real  perception 
on  the  part  of  the  animal,  or  whether  they  are  simply  automatic  reac- 
tions of  the  nervous  system,  like  the  contraction  and  dilatation  of  the 
pupil  in  a  person  who  is  unconscious.  It  is  certain  that,  if  impressions 
are  perceived  by  the  pigeon  after  removal  of  the  hemispheres,  they  are 
immediately  forgotten ;  and  furthermore  that  they  do  not  excite  any 
corresponding  series  of  ideas.  The  report  of  a  pistol  causes  no  sign 
of  alarm,  and  is  not  followed  by  any  attempt  at  escape ;  for  the  sound, 
even  if  perceived  by  the  animal,  does  not  suggest  any  idea  of  danger  or 
injury.  External  phenomena,  and  their  impressions  on  the  nervous 
system,  are  without  significance  for  the  animal ;  and  be  is  consequently 
no  longer  capable  of  originating  intelligent  volitional  acts. 

III.  In  man,  the  general  result  of  injury  or  disease  of  the  hemi- 
spheres is  a  disturbance  of  the  intellectual  faculties.  Among  the  earliest 
and  most  constant  of  these  phenomena  is  an  impairment  of  memory. 
The  patient  forgets  the  names  of  particular  objects  or  persons ;  or  he 
is  unable  to  calculate  numbers  with  his  usual  facility.  His  mental 
derangement  is  often  shown  in  the  undue  estimate  which  he  forms  of 
passing  events.  He  will  show  an  exaggerated  degree  of  solicitude 
about  a  trivial  occurrence,  while  he  pays  no  attention  to  matters  of  real 
importance.  As  the  difficulty  increases,  he  becomes  careless  of  direc- 
tions and  advice,  and  must  be  managed  like  a  child  or  an  imbecile. 
Finally,  when  the  injury  to  the  hemispheres  is  excessive,  the  sen.-is 
may  still  remain  impressible,  while  the  patient  is  completely  deprived 
of  intelligence.  The  frequency  of  these  results  in  lesions  of  the  hemi- 
spheres, without  loss  of  sensibility  or  motion,  shows  the  close  connec- 
tion between  the  mental  powers  and  the  nervous  action  of  this  portion 
of  the  brain. 

The  same  connection  is  seen  in  congenital  idiocy  with  imperfect 
development  of  the  brain.  In  many  cases  the  immediate  condition 
upon  which  idiocy  depends  is  the  small  size  of  the  brain  as  a  whole, 
and  particularly  that  of  the  cerebral  hemispheres.  The  general  and 
special  senses,  and  the  activity  of  the  nervous  system  at  large,  are 
sometimes  fully  developed  in  idiots,  while  the  intelligence  remains  at 
so  low  a  grade,  that  no  improvement  in  the  mental  operations  is  pus.-i- 
l>le,  and  instruction  is  consequently  without  effect. 


THE    BRAIN.  425 

The  mental  endowments  chiefly  concerned  in  the  manifestations  of 
intelligence  are  memory,  reason,  and  judgment. 

Memory  is  the  simplest  and  most  essential  of  these  faculties  for  the 
performance  of  intelligent  acts.  The  recollection  of  names,  and  of  the 
objects  to  which  they  belong,  is  indispensable  for  even  the  use  of  articu- 
late language ;  and  a  defective  memory  often  seems  the  immediate 
cause  of  the  incapacity  of  idiotic  children.  Memory  is  constantly 
essential  in  the  ordinary  occupations  of  life,  in  enabling  us  to  retain 
past  impressions  as  a  guide  for  immediate  or  future  acts. 

Reason  may  be  considered  as  the  ability  to  appreciate  the  nature  of 
nervous  impressions,  and  to  refer  them  to  their  external  source.  This 
is  quite  different  from  the  simple  power  of  perception,  which  may  con- 
tinue unimpaired  after  extensive  injury  of  the  hemispheres.  The  mental 
action  excited  by  an  impression  on  the  senses  transfers  our  attention 
from  the  sensation  to  its  cause ;  and  when  this  action  is  prompt  and 
effectual,  we  acquire  an  idea  both  of  the  origin  of  the  impression  and 
its  significance.  The  perfection  of  this  quality  consists  in  the  certainty 
with  which  it  appreciates  the  relation  between  cause  and  effect  and 
the  relative  importance  of  different  phenomena.  It  is  deficient  or 
absent  in  idiots,  and  they  consequently  cannot  avoid  dangers,  or  provide 
for  their  necessities.  For  the  same  reason  it  is  useless  to  punish  an 
idiot,  because,  although  he  may  feel  the  pain  inflicted,  he  does  not  refer 
it  as  a  consequence  to  any  previous  act  of  his  own.  A  similar  defi- 
ciency in  the  insane  or  the  weak-minded  produces  a  want  of  power  to 
comprehend  the  importance  and  connection  of  different  events.  They 
are  said  to  be  "unreasonable,"  because  they  expect  results  which  are 
unlikely  to  follow  from  certain  causes,  and  because  they  assume  the 
existence  of  causes  which  are  not  indicated  by  the  results. 

Judgment  is  the  faculty  by  which  appropriate  means  are  selected  for 
the  accomplishment  of  a  particular  end.  Its  exercise  requires  the 
existence  of  reason  and  memory,  which  supply  the  necessary  conditions 
upon  which  it  is  based ;  while  its  own  action  is  one  which  looks  to  the 
future  rather  than  to  the  past.  An  individual  in  whom  the  judgment  is 
well  developed  employs,  under  the  guidance  of  experience,  means  which 
are  adapted  to  the  end  in  view ;  one  who  is  deficient  in  this  respect 
resorts  to  means  which  are  insufficient  or  inappropriate,  and  is  conse- 
quently unsuccessful.  Whether  the  act  performed  in  this  manner  be  a 
simple  mechanical  operation,  like  that  of  shutting  a  door  to  exclude 
the  cold,  or  a  complicated  plan  involving  many  parts,  the  mental 
process  is  the  same  in  kind,  and  differs  only  in  degree ;  its  essential 
character  being  that  it  is  an  intelligent  act,  based  on  an  understanding 
of  the  previous  conditions,  and  intended  to  accomplish  a  definite  result. 

It  is  evident  that  all  such  manifestations  of  intelligence  are  in  the 
nature  of  reflex  actions.  Their  starting  point  is  a  sensation  coming 
from  without,  giving  rise  in  the  nervous  system  to  a  series  of  internal 
operations,  and  terminating  in  an  intelligent  volitional  impulse.  This 
is  reflected  from  within  outward,  and  thus  finally  calls  into  action  the 


426  THE    XERVOUS    SYSTEM. 

voluntary  muscles.  The  intermediate  process,  between  the  sensation 
and  the  volition,  may  be  short  and  simple ;  or  it  may  be  long  and 
complicated,  involving  the  continued  suggestion  of  many  successive 
ideas.  There  can  be  little  doubt  that,  in  either  case,  it  is  accompanied 
by  actions  of  some  kind  in  the  gray  substance  of  the  cerebral  hemi- 
spheres; for  if  these  organs  are  injured  or  defective,  the  mental  opera- 
tions are  obstructed  or  disturbed. 

But  the  nature  of  the  nervous  process  accompanying  mental  action 
is  unknown.  Physiological  research  gives  us  no  information  with 
regard  to  the  brain  as  an  organ  of  intelligence,  beyond  the  fact  that  it 
is,  in  some  way,  essential  to  its  manifestation ;  and  all  the  modern 
investigations  into  its  structure  and  physiological  properties  have  failed 
to  increase,  in  any  essential  particular,  our  knowledge  of  its  office  and 
action  in  the  operations  of  the  mind. 

Localization  of  Function  in  different  parts  of  the  Hemispheres. — 
On  the  other  hand,  the  most  valuable  information  has  been  obtained  of 
late  years  from  the  study  of  the  simpler  nervous  functions  and  their 
localization  in  different  parts  of  the  hemispheres.  The  recent  improve- 
ments in  our  knowledge  of  cerebral  physiology  relate  almost  entirely 
to  the  brain  as  an  organ  for  combining  and  regulating  the  nervous 
mechanism  of  conscious  sensations  and  voluntary  movements.  They 
show  that  certain  parts  of  the  cortex  of  the  hemispheres  are  connected 
with  phenomena  of  motion,  others  with  the  power  of  sensation  ;  while 
others  still,  so  far  as  yet  known,  are  indifferent  to  both  these  functions, 
and  are  perhaps  connected  with  nervous  acts  of  a  different  kind.  The 
hemispheres,  accordingly,  do  not  act  indiscriminately  as  a  whole ;  but 
the  convolutions  of  particular  regions  have  a  structure  and  properties 
differing  from  those  elsewhere.  The  knowledge  thus  far  obtained 
relates  chiefly  to  three  different  points,  namely,  1st.  Centres  of  Motion  ; 
2d.  Centres  of  Sensation ;  3d.  The  Centre  of  Language. 

I.  The  beginning  of  the  present  doctrine  on  this  subject  was  the  dis- 
covery, by  Fritsch  and  Hitzig*  in  1870,  of  the  centres  of  motion  in 
the  hemispheres  of  the  dog.  They  showed  that  galvanic  currents,  of 
low  intensity,  applied  to  certain  points  on  the  surface  of  the  convolu- 
tions, give  rise  to  definite  movements  of  the  head,  body,  or  limbs; 
while  no  such  effect  is  produced  by  galvanization  of  the  cerebral  sur- 
face in  other  regions.  These  experiments  were  subsequently  extended 
to  cats,  guinea-pigs,  rabbits,  and  monkeys.  They  have  been  confirmed 
by  many  other  observers  in  England,  France,  Italy,  and  the  United 
States,  and  we  have  repeatedly  verified  their  main  results,  f 

The  important  features  of  these  experiments  are  as  follows.  When 
the  animal  is  etherized,  and  the  convexity  of  the  hemisphere  exposed 
on  one  side  by  trephining  the  skull,  the  poles  of  a  galvanic  battery, 
applied  to  many  parts  of  the  convoluted  surface,  produce  no  visible 

*Archiv  fiir  Anatoraie,  Physiologie  und  wissmsrliaftliche   Medioin.      Leipzig, 
1870,  p.  300.     Hitzig,  Untersuchnngen  iiber  das  Gehirn.     Berlin,  1874. 
f  New  lork  Medical  Journal,  March,  1875,  p.  225. 


THE    BRAIN. 


427 


FIG.  113. 


result.  But  at  certain  circumscribed  localities,  the  application  of  the 
galvanic  stimulus  causes  definite  movements  of  the  limbs,  head,  or 
trunk.  These  movements  always  take  place  on  the  opposite  side 
of  the  body.  They  are  different  from  the  general  convulsive  reactions 
produced  by  galvanizing  the  spinal  cord,  the  trunk  of  a  spinal  nerve, 
or  the  base  of  the  brain.  They 
are  confined  to  particular  muscles 
or  groups  of  muscles,  and  produce 
flexion  or  extension  of  the  anterior 
or  posterior  limb  separately,  or  of 
a  single  joint  in  either.  They  are 
not  quite  instantaneous,  but  often 
have  a  certain  appearance  of  delib- 
eration, and  resemble  in  character 
the  normal  voluntary  movements 
in  a  waking  condition.  In  the 
same  animal,  particular  move- 
ments, such  as  flexion  or  ex- 
tension of  the  fore  or  hind  paw, 
always  follow  galvanization  of 
particular  points  on  the  cerebral 
convolutions,  the  relation  be- 
tween the  spot  galvanized  and 
the  part  moved  remaining  inva- 
riable. The  spot  on  the  cerebral 
surface  which  thus  responds  to 
galvanization  by  the  movement  of 
a  particular  limb  or  part  of  a  limb 
is  therefore  called  the  "  centre  of 
motion  "  for  that  part.  In  differ- 
ent dogs  the  special  centres  of  mo- 
tion are  not  strictly  identical  in 
locality,  but  they  are  very  nearly 
so ;  and  the  region  within  which  these  centres  exist,  or  the  "  motor 
region,"  is  as  definitely  marked  as  any  other  anatomical  division  of  the 
brain.  It  comprises  chiefly  the  convolutions  surrounding  the  so-called 
"frontal  fissure,"  a  nearly  transverse  furrow  in  the  anterior  portion 
of  the  dog's  brain,  running  outward  for  a  short  distance  from  the  great 
longitudinal  fissure. 

It  was  for  some  time  a  matter  of  doubt  whether  the  localized  move- 
ments in  question  were  produced  by  stimulation  of  the  cortex,  or  whether 
they  were  due  to  a  diffusion  of  the  galvanic  current  and  consequent  irri- 
tation of  more  deeply-seated  parts,  especially  the  corpora  striata.  But 
this  doubt  is  no  longer  entertained  by  the  majority  of  physiologists. 
When  the  distance  between  the  two  electrodes,  and  therefore  the  length 
of  the  current  traversing  the  convolution,  is  only  one  millimetre,  galvan- 
ization of  a  particular  spot  may  produce,  many  times  in  succession,  a 


BRAIN  OF  THE  DOG,  from  above ;  showing  centres 
of  motion  in  the  convolutions.  F.  Frontal  fis- 
sure. 1.  Flexion  of  head  on  neck,  in  the  median 
line.  2.  Flexion  of  head  on  neck,  with  rotation 
toward  the  side  of  the  stimulus.  3,  4.  Flexion 
and  extension  of  anterior  limb.  5,  6.  Flexion 
and  extension  of  posterior  limb.  7,  8,  9.  Con- 
traction of  orbicularis  oculi  and  other  facial 
muscles. 


428  THE    NERVOUS    SYSTEM. 

definite  muscular  contraction  ;  and  yet  the  application  of  the  electrodes 
to  neighboring  spots,  not  more  than  five  millimetres  distant  from  the 
first  and  equally  near  the  base  of  the  brain,  may  be  without  effect.  Fer- 
rier  *  has  found,  in  experiments  on  monkeys,  that  stimulation  of  the  con- 
volutions of  the  insula,  which  lie  in  close  proximity  to  the  corpus  stri- 
atum,  produces  no  visible  result ;  while  that  of  the  more  distant  con- 
volutions in  the  motor  region  on  the  surface  of  the  hemisphere  causes 
an  immediate  and  definite  movement.  Lastly,  decisive  proof  is  sup- 
plied by  the  experiments  of  Braunf  and  Putnam.^  In  these  experi- 
ments points  were  found  on  the  cerebral  convolutions  where  electric 
stimulus  produced  the  usual  definite  muscular  contractions.  A  hori- 
zontal section  was  then  made  one  or  two  millimetres  beneath  the 
surface,  leaving  the  flap  in  place  but  cutting  off  the  anatomical  con- 
tinuity of  brain  tissue.  The  irritation,  then  reapplied  to  the  original 
spot,  failed  to  excite  muscular  contraction ;  but  if  the  flap  were  turned 
up  and  the  electrodes  applied  to  the  cut  surface  beneath,  a  current  of 

FIG.  114. 


s' 

BRAIN  OP  THE  DOG;  profile  view,  showing  centres  of  motion  in  the  convolutions.  F.  Frontal 
fissure.  S.  Fissure  of  Sylvius.  1.  Flexion  of  head  on  neck,  in  the  median  line.  2.  Flexion  of 
head  on  neck,  with  rotation  toward  the  side  of  the  stimulus.  3,4.  Flexion  and  extension  of 
anterior  limb.  5,  6.  Flexion  and  extension  of  posterior  limb.  7,  8,  9.  Contraction  of  orbiculuris 
oculi  and  other  facial  muscles. 

similar  or  slightly  increased  strength  produced  the  same  movements 
as  before.  Repeated  trials  of  this  kind,  the  flap  being  alternately 
removed  and  readjusted,  yielded  the  same  results.  It  is  evident, 
therefore,  that  when  the  electrodes,  applied  to  the  surface  of  the  unin- 
jured brain,  cause  movements  on  the  opposite  side  of  the  body,  this  is 
due  not  to  a  diffusion  of  the  electric  current  toward  the  base  of  1  he- 
brain,  but  to  a  nervous  stimulus  oriirimitirig  in  the  convolutions,  and 
thence  transmitted  by  the  fibres  of  the  while  substance. 

The  reality  of  the  motor  centres  in  the  cerebral  convolutions  is  cor- 
roborated by  other  important  facts  of  two  kinds. 

First.  The  cortical  substance  of  the  region  in  question  has  a  special 

*  The  Localization  of  Cerebral  Disease.     London,  1879,  p.  17. 
t  OntralMatt  fiir  die  medicinischen  Wissenschaften.     Berlin,  June  1,'i,  1*71.  i>. 
455. 

J  Boston  Medical  and  Surgical  Journal,  July  16,  1874. 


THE     BRAIN.  429 

anatomical  stfucture,  which  distinguishes  it  from  other  parts  of  the 
hemispheres.  In  the  investigations  of  Betz,  already  quoted  (page  419), 
it  was  found  that  in  the  brain  of  the  dog  the  motor  region  about  the 
frontal  fissure  was  that  which  contained  in  its  gray  substance  the 
"giant  pyramidal  cells,"  similar  in  size  to  the  cells  of  the  anterior 
horns  in  the  spinal  cord,  and  exclusively  existing  in  the  cortical  layer 
of  this  part  of  the  brain.  The  microscopic  structure  of  these  convolu- 
tions has  therefore  an  individual  character,  corresponding  with  their 
physiological  properties. 

Secondly.  Extirpation  of  the  motor  centres  in  the  cerebral  convolu- 
tions produces  more  or  less  paralysis  of  voluntary  motion  on  the  oppo- 
site side  of  the  body.  This  has  been  shown  in  experiments  on  dogs 
by  Hitzig,  Schiff,  Hermann,  and  Carville  and  Duret.* 

The  paralysis  affects  special  movements,  according  to  the  particular 
seat  of  the  lesion  ;  and  when  a  certain  spot  on  the  cerebral  convolutions 
has  been  found  by  stimulation  to  excite  movements  of  flexion  or  exten- 
sion in-  one  of  the  opposite  limbs,  its  extirpation  causes  paralysis  of 
the  same  movement.  But  the  paralysis  thus  produced  varies  in  extent 
and  duration  in  different  animals.  In  the  pigeon,  removal  of  an  entire 
hemisphere  hardly  interferes  with  the  acts  of  standing  or  locomotion. 
In  the  dog,  destruction  of  the  motor  centres  on  one  side  causes  a  par- 
tial hemiplegia,  which  htfs  a  distinct  effect  on  locomotion,  but  which 
after  some  days  or  weeks  gradually  disappears,  the  animal  recovering 
his  natural  power  of  movement.  In  the  monkey,  according  to  Terrier, 
the  hemiplegia  from  this  cause  is  strongly  marked,  and  shows  no  indi- 
cation of  amendment;  while  in  man,  according  to  numerous  patho- 
logical observations,  it  is  absolutely  complete  and  permanent. 

This  difference  is  explained  by  supposing  that  in  the  lower  animals 
the  movement  of  the  limbs  in  locomotion  is  mainly  confined  to  con- 
sentaneous acts,  in  which  direct  volition  takes  a  small  share ;  while 
in  the  higher  animals,  and  especially  in  man,  the  influence  of  imme- 
diate volitional  impulses  is  more  essential,  and  preponderates  in 
importance,  according  to  the  number  and  variety  of  the  muscular 
actions. 

In  man,  the  motor  region  of  the  cerebral  hemispheres  comprises  in 
general  terms  the  convolutions  about  the  fissure  of  Rolando,  and  espe- 
cially the  anterior  and  posterior  central  convolutions.  It  would  hardly 
be  possible  to  assume  this  from  the  analogies  of  external  configuration, 
since  the  comparative  size  of  the  hemispheres  and  the  proportion  of 
their  various  parts  differ  so  widely  in  the  dog's  brain  and  that  of  man ; 
but  it  is  made  certain  by  anatomical  and  experimental  facts,  as  well  as 
by  the  result  of  observation  in  disease.  In  man  it  is  the  convolutions 
surrounding  the  fissure  of  Rolando  which  present,  like  those  of  the 
motor  region  in  the  dog's  brain,  the  special  structure  characterized  by 
the  presence  of  "  giant  pyramidal  cells,"  which  are  not  found  elsewhere. 

*  Archives  de  Physiologie.     Paris,  1875,  2me  serie,  tome  ii.,  p.  352. 


430  THE    NERVOUS    SYSTEM. 

Furthermore,  in  the  experiments  on  the  monkey  by  Ferrier,*  which 
have  given  to  this  subject  a  great  extension,  the  motor  centres  were 
found  to  occupy  a  similar  region.  In  this  animal  the  general  form  of 
the  hemispheres  is  so  similar  to  that  in  man  that  the  principal  fissures 
and  convolutions  can  be  recognized  without  difficulty  ;  and  by  stimu- 
lating various  points  of  the  anterior  and  posterior  central  convolutions, 
with  others  more  or  less  closely  adjacent,  the  same  kind  of  definite 
movements  are  produced  as  in  the  dog  by  stimulation  of  the  motor 
region. 

Lastly,  in  man,  there  is  now  a  large  body  of  evidence  to  the  same 
effect.  It  consists  of  numerous  cases  observed  or  reported  by  Charcot,f 
Ferrier, J  Rendu,§  and  Grasset,||  in  which  there  were  local  epileptiform 
convulsions  on  one  side  coexisting  with  irritation  of  the  opposite  cen- 
tral convolutions,  or  hemiplegia  caused  by  their  disorganization.  Ac- 
cording to  Rendu,  local  lesions  of  small  extent,  when  seated  in  the 
motor  region,  produce  hemiplegia;  while  others  of  large  area,  some- 
times occupying  nearly  a  whole  lobe,  if  outside  this  region,  are  not 
accompanied  by  paralysis.  The  hemiplegia  in  man,  resulting  from  dis- 
organization of  the  cortex  in  the  motor  region,  is  complete  and  perma- 
nent, and  is  not  associated  with  any  loss  of  sensibility. 

II.  The  centres  of  sensation  in  the  cortex  of  the  brain  have  not 
been  localized  to  the  same  extent  nor  with  the  same  certainty  as  the 
centres  of  motion.  There  is  reason  to  believe  that  the  power  of  per- 
ception for  sensitive  impressions  in  general  has  its  seat  in  some  part 
of  the  cerebral  cortex,  and  that  it  is  located  in  the  posterior  region 
of  the  hemispheres ;  since  a  loss  of  sensibility  on  the  opposite  side  of 
the  body,  both  in  the  higher  animals  and  in  man,  is  produced  by 
lesions  of  the  posterior  part  of  the  internal  capsule.  According  to  the 
experiments  of  Flourens,T  all  distinct  perception,  both  general  and 
special,  disappears  in  the  pigeon  after  removal  of  both  hemispheres ; 
and  after  removal  of  a  single  hemisphere  sight  is  abolished  in  the  eye 
of  the  opposite  side. 

The  power  of  visual  perception  is  especially  located  by  Ferrier**  in 
the  angular  convolution.  This  observer  found  that,  in  the  dog,  the 
cat,  and  the  monkey,  electrical  stimulation  of  this  convolution  caused 
rotation  of  the  eyeballs  and  sometimes  turning  of  the  head  toward  the 
opposite  side,  with  contraction  of  the  pupils,  as  if  from  a  visual  sensa- 
tion ;  and  in  the  monkey  destructive  lesions  of  the  angular  convolution 
produced  blindness  of  the  opposite  eye,  while  vision  remained  in  the 


*  Functions  of  the  Brain.     London,  1876. 

f  Lefons  sur  les  Localisations  dans  les  Maladies  du  Cervean.    Paris,  1878,  p.  166. 
J  Tin-  Locali/ation  of  Cerebral  I)israsr.     London,  1879,  p.  4%_!. 
§  Revue  des  Sciences  Mrdicales.     Paris,  1879,  tome  xiii.,  p.  314. 
||  D'.-s  Localisations  dans  U-s  Maladies  Chorales.     Paris,  1880,  p.  143. 
1f  Recherches  Experimentales  sur  les  Proprie'te's  et  les  Fonctions  du  Systeme  Ner- 
veux.     Paris,  1842,  pp.  31,  123. 
**  Functions  of  the  Brain.     London,  1876,  p.  180. 


THE     BRAIN. 


431 


eye  of  the  same  side.  After  unilateral  destruction  of  the  angular  con- 
volution, vision  returned  to  some  extent  in  the  blinded  eye  after 
twenty-four  hours ;  but  if  the  convolution  were  destroyed  on  both 
sides,  blindness  was  complete,  and  there  was  no  return  of  sight  in 
either  eye.  The  operation  produced  no  other  effect  than  loss  of  vision ; 
general  sensibility  and  the  power  of  motion  being  unimpaired. 

FIG.  115. 


BUAIN  OP  DOG;  shoeing  excision  of  angular  convolution  and  two  adjacent  anterior  convolutions 
on  left  side.    Blindness  of  right  eye. 

We  have  obtained  similar  results  in  the  dog  by  excision  of  the 
angular  convolution  on  the  right  and  left  sides  in  two  different  animals. 


FIG.  116. 


BRAIN  OF  DOG  ;  showing  excision  of  angular  convolution  and  adjacent  posterior  convolution  on 
right  side.    Blindness  of  left  eye. 

In  each  case  vision  remained  perfect  in  the  eye  of  the  same  side  with 
the  injury,  but  was  abolished  in  the  eye  of  the  opposite  side.  There 
was  no  other  perceptible  affection  of  either  sensibility  or  movement ; 
and  the  blindness  of  the  affected  eye  was  persistent  during  the  life  of 
the  animal,  continuing  in  one  instance  for  over  ten  days.  It  appears 
accordingly  highly  probable  that  the  power  of  visual  perception  is 
seated  in  that  part  of  the  cortex  occupied  by  the  angular  convolution. 


432  THE    NERVOUS    SYSTEM. 

III.  Thero  is  at  present  no  doubt  as  to  the  existence  in  the  cerebral 
cortex  of  a  centre  of  language — that  is,  of  a  region  which,  in  man,  pre- 
sides over  the  necessary  combinations  for  articulate  speech.  Many 
animals  have  the  power  of  communicating  with  each  other  by  cer- 
tain movements  and  sounds  in  such  a  way  as  to  attract  attention, 
and  enable  them  to  act  in  concert.  The  language  thus  employed  is  a 
language  of  expression,  and  consists  in  such  modifications  of  the  tone 
of  voice  or  position  of  the  limbs  as  indicate  pleasure  or  dislike,  excite- 
ment or  alarm,  or  a  friendly  or  hostile  disposition.  In  man  the  same 
methods  are  largely  used  to  express  similar  feelings,  and  to  represent 
others,  such  as  surprise,  contempt,  amusement,  or  doubt,  which  do  not 
seem  to  exist  in  animals  to  an  appreciable  degree. 

But  man  has  also  the  faculty  of  conveying  definite  information  by 
means  of  articulate  speech,  in  which  arbitrary  sounds  are  used  to  indi- 
cate special  objects,  qualities,  or  acts,  as  well  as  the  relations  between 
them.  The  power  of  using  articulate  language  for  the  expression  of 
thought  is  usually  in  proportion  to  the  development  of  the  general 
intelligence.  In  order  that  it  may  be  exercised,  two  faculties  must 
come  into  action,  namely,  first,  the  memory,  by  which  the  particular 
words  required  are  brought  to  the  mind ;  and,  secondly,  the  voluntary 
combination  of  movements  necessary  for  articulation.  These  acts  are 
performed,  in  health,  with  such  rapidity  that  we  are  not  conscious  of 
them ;  and  articulate  speech  seems  tc  be  a  direct  sequence  of  our  inter- 
nal ideas.  But  pathological  cases  show  that  either  one  or  both  of  the 
above  faculties  may  be  absent,  while  the  ideas  and  the  desire  to  express 
them  are  as  distinct  as  ever. 

This  affection  is  termed  aphasia.  It  does  not  depend  upon  a  want 
or  confusion  of  ideas,  because  the  patient  is  often  perfectly  clear  as 
to  what  he  wishes  to  say,  although  he  cannot  say  it.  It  is  not 
due  to  paralysis  of  the  organs  of  articulation,  since  the  tongue,  lips, 
and  palate  can  be  moved  for  other  purposes,  in  any  direction,  with  the 
usual  facility.  It  is  an  inability  either  to  recall  the  word  needed,  or 
to  set  in  motion  the  nervous  actions  required  to  pronounce  it.  In  the 
former  instance  it  is  called  "amnesic  aphasia."  The  patient  cannot 
say  what  he  wishes,  because  he  cannot  recollect  the  word  he  wants. 
For  the  same  reason  he  is  also  incapable  of  writing  it.  But  if  the 
word  which  he  requires  be  pronounced  for  him,  he  recognizes  it,  and 
can  repeat  it,  though  in  a  few  seconds  it  has  again  escaped  him.  This 
disease  is  an  aggravated  form  of  the  condition  to  which  many  other- 
wise healthy  persons  are  liable,  namely,  that  of  sometimes  forgetting 
a  particular  word  at  the  moment  it  is  required  for  use.  In  some 
cases  of  aphasia  the  loss  of  power  is  so  complete  that  the  patient 
can  utter  only  two  or  three  words,  which  he  employs  indiscriminately 
on  all  occasions. 

In  the  second  variety  of  the  affection  the  patient  knows  the  word 
he  wants,  but  cannot  articulate  it.  He  can,  therefore,  express  himself 
perfectly  well  by  writing,  but  is  unable  to  read  uloud  even  what  he  has 


THE    BRAIN.  433 

written.  This  is  called  "ataxic  aphasia,"  because  it  depends  upon  a 
defect  of  nervous  combination. 

Observations  on  the  locality  of  the  centre  of  language  tend  to  place 
it  more  especially  in  the  convolutions  surrounding  the  lower  end  of  the 
fissure  of  Sylvius,  and  in  those  of  the  insula.  Broca  refers  it  to  the 
posterior  part  of  the  third  frontal  convolution,  while  others  consider  it 
as  belonging  to  the  frontal  lobe  in  general.  The  evidence  for  this  local- 
ization consists  in  a  number  of  instances  in  which  aphasia  has  been 
found,  on  post-mortem  examination,  to  be  accompanied  by  lesions  of 
the  brain  confined  to  the  points  indicated.  It  is  often  accompanied  by 
hemiplegia,  but  may  exist  independently  of  any  paralytic  affection. 

According  to  the  majority  of  observers,  the  nervous  centre  for 
articulate  speech  is  seated  upon  one  side  of  the  brain  only,  and,  as 
a  rule,  in  the  left  hemisphere.  This  conclusion  is  derived  from  the 
large  preponderance  of  cases  in  which  aphasia  is  associated  with 
hemiplegia  on  the  right  side  of  the  body  rather  than  on  the  left.  It 
is  still  more  strongly  corroborated  by  such  instances  as  that  reported 
by  Bateman,*  of  chronic  left  hemiplegia  without  aphasia,  followed  in 
the  same  individual  by  a  sudden  attack  of  right  hemiplegia  with 
aphasia.  It  is  not  supposed  that  the  two  hemispheres  are  absolutely 
different  from  each  other  in  this  respect ;  but  that  the  functional 
superiority  of  the  left  side,  in  the  production  of  language,  is  like  that 
by  which  we  are  enabled  to  use  the  right  hand  for  certain  delicate 
manipulations  of  which  the  left  is  incapable.  A  lesion  of  the  motor 
centres  in  the  right  hemisphere  would  paralyze  only  the  ordinary 
movements  effected  by  the  left  hand ;  but  a  lesion  of  the  same  extent 
in  the  left  hemisphere  would  further  paralyze  the  special  movements, 
like  writing  or  drawing,  for  which  we  depend  on  the  right  hand.  It 
is,  perhaps,  for  a  similar  reason  that  a  patient  with  destructive  injury 
of  the  left  hemisphere  becomes  incapable  of  language,  while  one  with 
a  corresponding  injury  on  the  right  side  is  not  affected  in  the  same 
way.  This  would  also  explain  the  exceptional  cases  in  which  aphasia 
coincides  with  left  hemiplegia  ;  just  as  certain  individuals  are  habitually 
left-handed,  and  would  consequently  be  rendered  incapable  of  delicate 
manipulations  by  hemiplegia  of  the  left  side. 

Hemiplegia  and  Hemiansesthesia  from  Cerebral  Lesions. — It  has 
already  been  shown  that  hemiplegia  of  the  opposite  side  of  the  body, 
without  alteration  of  sensibility,  results,  in  man,  from  destructive 
lesions  of  the  cerebral  convolutions  in  the  motor  region.  It  is  also 
known  that  hemiansesthesia,  or  loss  of  sensibility  in  one  lateral  half 
of  the  body,  may  take  place,  without  paralysis  of  motion,  from  cerebral 
disease.  Both  these  affections  may  furthermore  be  produced  by  lesions 
limited  to  particular  parts  of  the  white  substance.  This  substance 
consists  of  tracts  connecting  the  cortical  convolutions,  through  the 
corona  radiata  and  internal  capsule,  with  the  base  of  the  brain,  and 

*  On  Aphasia.     London,  1870,  p.  152. 
2C 


434  THE    NERVOUS    SYSTEM. 

finally  with  the  peripheral  organs.  If  these  tracts  be  injured  in  any 
part  of  their  course,  hemiplegia,  hemianaesthesia,  or  both,  may  follow 
as  a  consequence. 

The  locality  of  lesions  producing  hemiplegia  is  in  the  anterior  por- 
tion of  the  internal  capsule.  In  the  experiments  on  dogs  by  Carville 
and  Duret,*  section  of  the  internal  capsule  in  this  region,  between  the 
caudate  nucleus  and  the  lenticular  nucleus,  was  constantly  followed  by 
hemiplegia  of  the  opposite  side  of  the  body.  In  man,  the  results  of 
pathological  observation  are  to  the  same  effect.  According  to  Charcot,f 
although  destructive  lesions,  limited  to  the  gray  substance  of  the  corpus 
striatum  or  optic  thalamus,  may  produce  symptoms  of  hemiplegia,  the 
paralysis  in  these  instances  is  usually  incomplete  and  transitory :  and 
is  often  to  be  referred,  in  cases  of  hemorrhagic  effusion,  to  temporary 
compression  of  the  internal  capsule.  On  the  other  hand,  lesions  con- 
fined to  the  internal  capsule,  in  its  anterior  two-thirds,  produce  an  oppo- 
site hemiplegia  which  is  strongly  marked  and  persistent,  and  usually 
unaccompanied  by  any  loss  of  sensibility.  The  destruction  of  conti- 
nuity in  the  fibres  of  the  internal  capsule  from  such  injuries  is  final,  and 
the  resulting  paralysis  is  consequently  permanent. 

The  production  of  hemianaesthesia  from  lesions  of  the  internal  cap- 
sule is  limited,  in  an  analogous  way,  to  its  posterior  portion.  The 
region  of  cortical  substance  devoted  to  the  perception  of  tactile  sensa- 
tions has  not  been  determined  to  the  general  satisfaction  of  physi- 
ologists. But  there  is  reason  to  believe  that  it  is  seated  somewhere 
in  the  posterior  portion  of  the  hemisphere ;  and  there  is  no  question 
that  the  communicating  tracts  of  centripetal  fibres,  subservient  to  this 
function,  are  in  the  hinder  part  of  the  internal  capsule.  The  extreme 
posterior  border  of  this  capsule  is  formed  by  the  direct  sensitive  fibres 
from  the  outer  part  of  the  crura  cerebri  already  mentioned  (page  422) 
as  described  by  Gratiolct.  In  the  experiments  of  VeyssiereJ  on  dogs, 
it  was  shown  that  for  the  production  of  persistent  hemiana3sthesia 
from  cerebral  lesions,  it  was  indispensable  that  the  injury  involve 
the  fibres  of  the  internal  capsule. 

According  to  the  researches  of  Carville  and  Duret,  already  quoted, 
it  appears  that  while  a  destructive  injury  in  the  anterior  portion  of  the 
internal  capsule  causes  hemiplegia  without  hemianaesthesia,  a  lesion  of 
its  posterior  portion  is  followed  by  hemiansesthesia  without  hemiplegia. 
In  each  case  the  morbid  effects  are  produced  on  the  opposite  side  of 
the  body.  The  same  rule  holds  good  in  man.  According  to  Charcot, 
the  question  whether  a  lesion  in  the  neighborhood  of  the  cerebral 
ganglia  shall  produce  loss  of  motion  or  loss  of  sensibility  depends  on 
which  part  of  the  internal  capsule  it  involves.  If  seated  in  the  anterior 
two-thirds  it  produces  hemiplegia ;  if  in  the  posterior  third,  it  is  a  heini- 

*  Archives  de  Physiologic.     Paris,  1875,  2me  seVie,  tome  ii.,  p.  352. 
f  Lecons  sur  les  Localisations  dans  les  Maladies  da  Cerveau.     Paris,  1878,  pp.  96, 
98,  99, 100. 

t  IK'iuiaiuesth&ue  de  Cause  Cerdbrale.     Paris,  1874,  p.  73. 


THE    BRAIN.  435 

anaesthesia  which  results.  Hemianaesthesia  of  cerebral  origin,  accord- 
ing to  the  same  observer,  is  characterized  by  the  fact  that,  together 
with  loss  of  sensibility  in  the  body  and  limbs,  there  is  a  similar  insensi- 
bility in  the  integument  of  the  head  and  face,  and  in  addition  a  loss  or 
impairment  of  the  special  senses ;  taste,  smell,  hearing,  and  vision  being 
all  more  or  less  affected,  on  the  side  opposite  to  that  of  the  cerebral 
lesion.  This  will  serve  to  distinguish  hemianaesthesia  due  to  injury 
of  the  brain  from  that  caused  by  a  lesion  of  the  spinal  cord,  in  which 
the  only  symptom  present  is  loss  of  sensibility  on  one  side  of  the  body. 

The  Cerebellum. 

The  cerebellum,  though  much  inferior  in  size  to  the  cerebrum,  con- 
sists, like  it,  of  a  folded  cortical  gray  layer  surrounding  a  central  mass 
of  white  substance.  The  cortical  layer  is  only  about  one-half  as  thick 
as  that  of  the  cerebrum ;  being  nowhere  over  1.5  millimetre  in  thickness. 
But  its  convolutions  are  very  compactly  arranged  in  the  form  of  thin, 
closely  adjacent  laminae ;  so  that  it  contains  a  comparatively  large 
quantity  of  gray  substance. 

The  cortical  layer  of  the  cerebellar  convolutions  is  penetrated  by 
fibres  from  the  interior  white  substance,  and  contains  nerve  cells 
of  various  form  and  size.  The  most  characteristic  are  flask-shaped 
cells,  arranged  in  a  single  or  double  row ;  the  rounded  extremity 
of  each  cell  being  directed  inward,  the  pointed  extremity  outward. 
According  to  Kolliker  and  Henle,  the  cells  usually  give  off  prolonga- 
tions in  two  opposite  directions ;  that  which  passes  inward  toward  the 
white  substance  being  unbranched  and  resembling  the  axis-cylinder  of 
a  nerve  fibre,  while  that  which  passes  toward  the  surface  of  the  con- 
volution divides  into  numerous  ramifications. 

The  cerebellum  is  connected  with  the  rest  of  the  cerebro-spinal  axis, 
1st,  by  the  inferior  peduncles,  or  restiform  bodies,  which  come  from 
the  posterior  and  lateral  parts  of  the  medulla  oblongata,  to  radiate  in 
its  white  substance ;  and  2d,  by  the  superior  peduncles,  or  processus  e 
cerebello  ad  corpora  quadrigemina,  which  originate  from  the  cerebel- 
lum nearer  the  median  line  than  the  restiform  bodies,  and  thence  pass 
upward  and  forward,  joining  the  longitudinal  tracts  of  the  tuber  annu- 
lare  and  crura  cerebri.  3d,  The  two  lateral  halves  of  the  cerebellum 
are  furthermore  connected  with  each  other  by  the  middle  peduncles, 
which  originate  from  the  white  substance  on  each  side,  and  pass  forward 
and  downward  to  meet  in  front  upon  the  under  surface  of  the  tuber 
annulare,  forming  the  arched  commissure  of  the  pons  Varolii. 

Physiological  Properties  of  the  Cerebellum. — The  general  result  of 
experimental  operations  on  the  cerebellum  shows  that  the  surface  of 
this  organ  is  inexcitable  by  ordinary  means,  and  that  its  mechanical 
irritation  gives  no  evidence  of  sensibility.  Flourens,  Longet,  Vulpian, 
and  experimenters  in  general,  have  recognized  the  fact  that  neither 
sensation  nor  muscular  contractions  are  produced  by  touching  or 
wounding  its  external  gray  substance ;  while  in  its  deeper  portions 


436  THE    NERVOUS    SYSTEM. 

both  excitability  and  sensibility  become  manifest,  in  proportion  as  the 
irritation  is  applied  nearer  the  medulla  oblongata  and  the  inferior 
peduncles.  Furthermore,  its  removal,  either  in  part  or  in  whole,  does 
not  essentially  diminish  either  sensation  or  the  power  of  movement. 
The  senses  remain  active,  and  the  intelligence  is  unimpaired,  provided 
the  cerebral  hemispheres  are  intact.  If  injury  of  other  adjacent  parts 
be  avoided,  the  cerebellum  may  be  extensively  wounded  or  even  totally 
removed  in  many  animals  without  causing  death.  One-half  or  two- 
thirds  of  its  substance  have  often  been  taken  away  in  the  pigeon ;  and 
in  one  of  the  experiments  of  Flourens,  a  fowl  lived  for  more  than  four 
months  after  its  complete  extirpation. 

Aside  from  these  particulars,  experiments  consisting  in  mutilation 
or  removal  of  the  cerebellum  have  yielded  very  uniform  and  striking 
results,  quite  different  from  those  caused  by  injury  to  other  parts  of  the 
brain.  These  effects  were  first  described  by  Flourens,*  and  notwith- 
standing the  great  activity  of  research  since  that  time,  his  results  have 
been  corroborated  in  all  essential  particulars  by  subsequent  observers. 
They  have  been  witnessed,  by  different  observers,  in  the  pigeon,  fowl, 
duck,  turkey,  and  other  birds ;  and,  among  quadrupeds,  in  the  dog,  the 
cat,  the  mole,  the  rat,  and  the  guinea-pig. 

The  effect  produced  by  partial  or  complete  destruction  of  the  cere- 
bellum is  a  peculiar  disorder  of  movement  in  the  body  and  limbs,  from 
want  of  harmony  in  their  muscular  action.  The  power  of  associating 
different  muscles,  in  such  a  way  as  to  produce  coordinated  movements, 
is  impaired  in  proportion  to  the  extent  of  injury  to  the  nervous  centre. 
In  the  pigeon,  if  a  small  portion  only  of  the  cerebellum  be  removed, 
the  animal  exhibits  a  peculiar  uncertainty  in  the  gait,  and  in  the  move- 
ment of  the  wings.  If  the  injury  be  more  extensive,  the  power  of 
flight  is  lost  and  the  bird  can  walk,  or  even  stand,  only  with  difficulty. 
There  is  no  actual  paralysis,  for  the  movements  of  the  limbs  are  often 
rapid  and  energetic ;  but  there  is  a  want  of  control  over  the  muscular 
contractions,  similar  to  that  shown  by  a  man  in  a  state  of  intoxication. 
The  movements  are  confused  and  blundering  ;  so  that  the  animal  cannot 
direct  his  steps  to  any  particular  spot,  nor  support  himself  in  the  air  by 
flight.  He  reels  and  tumbles,  but  can  neither  walk  nor  fly. 

The  senses  and  the  intelligence  are  at  the  same  time  unaffected,  and 
this  causes  a  striking  difference  between  the  effects  produced  by  removal 
of  the  cerebrum  and  that  of  the  cerebellum.  If  these  operations  be  done 
upon  two  different  pigeons,  the  animal  from  which  the  cerebrum  only 
has  been  removed  will  remain  standing  upon  his  feet,  in  a  condition  of 
complete  repose ;  while  the  other,  from  which  the  cerebellum  has  been 
taken  away,  is  in  a  constant  state  of  agitation,  frequently  endeavoring, 
with  violent  and  ineffectual  struggles,  to  perform  movements  which  he 
cannot  accomplish. 

*Recherches  Exp^rimentales  sur  lea  Propri6t£s  et  les  Fonctions  du  SystSme 
Nerveux.  Paris,  1842,  pp.  37,  53,  102,  133. 


THE    BRAIN.  437 

The  inference  from  these  phenomena  is  that  the  power  of  coordi- 
nation for  voluntary  movements  resides  in  the  cerebellum,  and  is  im- 
paired by  injury  of  its  substance.  We  have  already  seen  (page  407)  that, 
for  the  body  and  limbs,  in  the  acts  of  standing  and  locomotion,  a 
power  of  coordination  exists  in  the  spinal  cord ;  and  that  it  apparently 
depends  on  the  integrity  of  the  posterior  columns,  which  serve  as  con- 
necting longitudinal  tracts  between  its  different  parts.  But  to  produce 
an  appreciable  disturbance  of  this  power  in  the  spinal  cord,  the  poste- 
rior columns  must  be  divided  at  several  successive  points ;  thus  disas- 
sociating its  parts  from  each  other  for  a  considerable  extent.  The 
cerebellum  is  the  only  nervous  centre  in  which  a  single  injury  produces 
a  want  of  coordination  for  all  voluntary  movements  whatever.  Accord- 
ing to  this  view,  it  is  a  nervous  centre  of  highly  developed  structure, 
superadded  to  the  cerebro-spinal  tracts,  for  the  complicated  association 
of  their  motor  impulses.  This  association  cannot  be  properly  carried 
out  in  any  particular  part,  unless  the  corresponding  peripheral  tracts  be 
also  in  a  state  of  integrity ;  but  it  is  in  the  gray  substance  of  the  cere- 
bellum that  the  nervous  coordination  is  originally  effected. 

Restoration  of  the  Coordinating  Power  in  Operated  Animals. — It  is 
a  remarkable  fact  that  after  the  coordinating  power  has  been  seriously 
impaired  by  partial  destruction  of  the  cerebellum,  it  may  in  some  in- 
stances be  recovered,  without  regeneration 'of  the  nervous  substance. 
This  recovery  was  observed  by  Flourens  both  in  the  fowl  and  in  the 
pigeon,  and  has  been  seen  by  Flint*  in  the  pigeon  after  removal  of 
about  two-thirds  of  the  cerebellum.  We  have  also  met  with  four  in- 
stances of  the  same  kind.  In  the  first,  about  two-thirds  of  the  cere- 
bellum were  taken  away  by  an  opening  in  the  posterior  part  of  the 

FIG.  117.  FIG.  118. 


BRAIN    OP     HEALTHY    PIGEON  —  Profile  BRAIN    OP    OPERATED    PIGEON  — Profile 

view.— 1.  Cerebral  Hemisphere.    2.  Optic  view  —  showing   the    mutilation  of  the 

Tubercle.  3.  Cerebellum.  4.  Optic  Nerve.  Cerebellum. 
5.  Medulla  Oblongata. 

cranium.  Immediately  afterward,  the  pigeon  showed  all  the  usual 
effects  of  the  operation,  being  incapable  of  flying,  walking,  or  even  of 
standing  still,  but  only  reeled  and  sprawled  in  a  perfectly  helpless  man- 
ner. In  five'  or  six  days  he  had  regained  a  considerable  control  over 
the  voluntary  movements,  and  at  the  end  of  sixteen  days  his  power 
of  muscular  coordination  was  so  nearly  perfect  that  its  deficiency,  if 


*  The  Physiology  of  Man  ;  Nervous  System.     New  York,  1872,  p.  367. 


438  THE    NERVOUS    SYSTEM. 

any  existed,  was  imperceptible.  He  was  then  killed,  and  on  examina- 
tion it  was  found  that  his  cerebellum  remained  in  nearly  the  same 
condition  as  immediately  after  the  operation ;  about  two-thirds  of  its 
substance  being  deficient,  with  no  regeneration  of  the  lost  parts.  The 
accompanying  figures  show  the  appearances  in  this  brain  as  compared 
with  that  of  a  healthy  pigeon. 

In  the  three  remaining  cases  the  quantity  of  nervous  substance 
removed  amounted  to  about  one-half  of  the  cerebellum.  The  loss  of 
coordinating  power,  immediately  after  the  operation,  though  less  com- 
plete than  in  the  preceding  instance,  was  perfectly  well  marked ;  and 
in  little  more  than  a  fortnight  the  animals  had  nearly  or  quite  recovered 
control  of  their  motions,  so  far  as  could  be  seen  while  they  were  under 
observation. 

It  is  evident  that  in  these  cases,  if  the  cerebellum  be  really  the  physi- 
ological seat  of  coordinating  power,  there  are  two  distinct  effects  pro- 
duced by  the  operation.  The  first  is  the  shock  due  to  the  sudden  injury 
of  the  cerebellum  as  a  whole.  This  effect  is  temporary,  and  may  be 
recovered  from  in  time,  provided  the  animal  survive  the  immediate 
injury.  The  remaining  effect  is  that  due  to  the  loss  of  nervous  sub- 
stance ;  and  this  effect  must  of  course  be  permanent,  unless  the  ner- 
vous matter  be  regenerated.  In  the  cases  detailed  above,  the  greatest 
amount  of  disturbance  seems  to  have  depended  on  the  sudden  injury 
to  the  nervous  centre  as  a  whole ;  and  the  animals  recovered,  to  a 
great  extent,  their  power  of  coordination,  notwithstanding  that  from 
one-half  to  two-thirds  of  the  cerebellum  was  permanently  lost. 

The  recovery  of  a  nervous  function,  after  loss  of  substance,  is  not 
peculiar  to  the  cerebellum.  Flourens  observed  the  same  thing  in 
regard  to  the  cerebral  hemispheres  in  the  pigeon :  the  perceptive 
faculties  being  totally  suspended  by  removal  of  a  portion  of  the  hemi- 
spheres, and  again  restored  after  several  days.  But  this  restoration 
only  takes  place  where  the  removal  of  the  nervous  centre  is  partial ; 
and  in  the  cerebellum,  as  well  as  in  the  cerebrum,  after  complete  extir- 
pation, the  loss  of  function  is  permanent.  In  the  experiment  of 
Flourens,  where  a  fowl  lived  for  four  months  after  entire  removal  of 
the  cerebellum,  there  was  no  recovery  of  coordinating  power. 

The  recovery  of  this  power  after  partial  loss  of  the  cerebellum  may 
be  also  in  some  measure  apparent  rather  than  real.  The  animals  may, 
after  a  time,  cease  attempting  the  more  complicated  movements  of  which 
they  are  incapable,  and  confine  themselves  to  the  simpler  acts  which 
they  can  still  accomplish.  A  pigeon,  furthermore,  when  confined  to 
the  limited  space  of  a  laboratory,  has  no  opportunity  for  the  many 
varied  evolutions  of  natural  flight ;  and  it  is  possible  that  he  might 
be  permanently  incapacitated  for  such  movements,  while  showing  no 
deficiency  in  the  ordinary  acts  of  standing  or  progression. 

The  same  remark  will  apply  to  certain  pathological  observations  in 
man,  which  have  been  sometimes  considered  as  neutralizing  the  results 
of  experiment  on  this  subject.  These  are  mainly  cases  in  which  lesions 


THE     BRAIN.  439 

of  the  cerebellum,  more  or  less  extensive,  have  existed  without  recorded 
disturbances  of  muscular  coordination.  A  large  majority  of  these 
patients  were  confined  to  a  sick-room,  and  many  of  them  to  the  bed ; 
consequently  there  could  be  no  opportunity  of  observing  a  want  of 
natural  coordination  in  the  more  complicated  movements,  if  any  such 
existed.  A  patient,  suffering  from  the  gradual  diminution  of  a  nervous 
function,  accommodates  himself  to  it  by  abstaining  from  the  attempt 
to  do  what  he  knows  is  impossible,  and  endeavors  to  accomplish  his 
objects  by  other  means.  Moreover,  in  many  cases  of  disease  of  the 
cerebellum,  symptoms  of  want  of  coordinating  power  have  been  dis- 
tinctly recorded. 

The  data  derived  from  comparative  anatomy  show  a  general  corre- 
spondence in  the  development  of  the  cerebellum  and  the  variety  of 
muscular  action.  In  fish,  as  a  rule,  it  is  of  good  size  compared  with 
other  parts  of  the  brain ;  and  although  direct  progression  in  this  class 
is  accomplished  by  a  comparatively  simple  mechanism,  namely,  the 
lateral  flexion  and  extension  of  the  spinal  column  with  its  expanded 
fins  and  tail,  yet  their  movements  through  the  water  or  in  leaping 
out  of  it,  while  pursuing  and  taking  their  prey,  are  rapid  and  vigorous, 
and  are  promptly  varied  in  any  direction.  In  the  frog,  on  the  other 
hand,  the  movements  of  progression  consist  of  little  else  than  straight- 
forward flexion  and  extension  of  the  posterior  limbs ;  and  the  cerebel- 
lum is  much  inferior  in  size  to  that  of  fishes,  forming  only  a  thin 
narrow  ribbon  of  nervous  matter  across  the  upper  part  of  the  fourth 
ventricle.  In  turtles,  locomotion  is  accomplished  by  consentaneous 
action  of  the  anterior  and  posterior  limbs,  while  the  cerebellum  exhibits 
a  corresponding  increase  of  development.  In  the  alligator,  whose  mo- 
tions approximate  still  more  closely  to  those  of  the  quadrupeds,  the 
cerebellum  is  also  larger  in  proportion  to  the  remaining  parts  of  the 
brain.  In  birds,  in  quadrupeds,  and  in  man  there  is  a  very  evident 
increase  in  the  size  and  convolutions  of  the  cerebellum,  corresponding 
with  the  greater  variety  and  delicacy  of  their  movements.  These  facts 
are  not  decisive  in  determining  the  physiological  function  of  this  por- 
tion of  the  brain  ;  but  they  show  that  the  assumption  of  a  coordinating 
power  in  the  cerebellum  is  not  at  variance  with  its  comparative  anatomy. 

All  that  we  know  with  certainty,  therefore,  in  regard  to  the  cerebel- 
lum, indicates  its  close  connection  with  the  power  of  coordination.  By 
its  inferior  peduncles  it  is  in  communication  with  the  posterior  columns 
of  the  spinal  cord,  and  by  its  superior  peduncles  with  the  upper  portion 
of  the  crura  cerebri ;  and,  so  far  as  its  function  can  be  demonstrated 
from  experiment,  it  appears  to  act  as  a  general  centre  of  combination 
for  voluntary  movement. 


The  Medulla  Oblongata. 

The  medulla  oblongata  is  distinguished  from  the  spinal  cord,  of  which 
it  forms  the  direct  continuation,  by  its  expanded  form,  the  different 


440  THE    NERVOUS    SYSTEM. 

appearance  of  its  longitudinal  tracts,  and  especially  by  the  changed 
position  and  special  properties  of  its  gray  substance. 

The  arrangement  of  the  gray  substance  is  one  of  the  most  character- 
istic features  of  the  medulla  oblongata.  First,  it  increases  in  quantity 
from  below  upward ;  and,  secondly,  it  undergoes  a  complete  alteration 
in  form  and  position.  In  the  spinal  cord  it  presents  the  well-known 
figure,  on  transverse  section,  of  a  central  mass  extending  on  each  side 
into  the  anterior  and  posterior  horns.  But  in  the  medulla  oblongata 
it  recedes  into  a  backward  position  ;  its  posterior  horns  spreading  out 
laterally,  and  the  remainder  occupying  the  space  between  them.  The 
posterior  median  fissure  also  becomes  shallower  and  wider  by  the  diver- 
gence of  the  posterior  columns  ;  and  the  central  canal  approximates  the 
posterior  wall  of  the  medulla,  finally  opening  upon  its  surface  at  the 
lower  part  of  the  fourth  ventricle.  The  gray  substance  of  the  medulla 
is  thus  uncovered  posteriorly,  forming  a  superficial  layer  on  each  side 
the  median  line,  immediately  beneath  the  floor  of  the  fourth  ventricle. 
It  thence  extends  forward,  without  complete  interruption,  through  the 
whole  length  of  the  fourth  ventricle  and  about  the  aqueduct  of  Sylvius  ; 
giving  origin,  at  various  points  in  this  situation,  to  the  root-fibres  of 
all  the  cranial  nerves,  excepting  the  olfactory  and  the  optic. 

Physiological  Properties  of  the  Medulla  Oblongata. — The  physio- 
logical properties  of  the  medulla  are  more  distinctly  marked  than  those 
of  any  other  part  of  the  encephalic  mass.  It  is  in  a  high  degree  both 
sensitive  and  excitable,  especially  in  its  posterior  portions.  Either 
mechanical  or  galvanic  irritation  gives  rise  at  once  to  signs  of  sensa- 
tion, if  the  rest  of  the  brain  be  uninjured,  and  in  the  recently  killed  ani- 
mal produces  convulsive  movements  of  considerable  intensity.  These 
effects  are  due  to  irritation  of  the  longitudinal  fibres  connecting  the 
medulla  with  the  spinal  cord,  and  of  the  sensitive  and  motor  cranial 
nerve  roots.  Since  the  medulla  is  the  only  bond  of  nervous  communi- 
cation between  the  brain  and  the  spinal  cord,  its  section  at  any  point 
also  destroys  voluntary  motion  and  sensibility  in  the  body  and  limbs. 

Action  of  the  Medulla  Oblongata  as  a  Nervous  Centre. — The  various 
deposits  of  gray  substance  in  the  medulla,  and  their  connection  with 
nerves  of  widely  different  distribution  and  functions,  are  the  peculiar 
features  of  its  anatomical  structure ;  while  its  reflex  actions  are  also  of 
a  special  and  distinctive  character. 

The  most  important  action  of  the  medulla  as  a  nervous  centre  is  that 
connected  with  respiration.  So  long  as  the  medulla  is  uninjured,  al- 
though the  cranium  be  emptied  of  all  its  other  nervous  centres,  respi- 
ration goes  on  without  essential  modification.  But  if  the  other  parts 
of  the  brain  be  left  intact  and  the  medulla  be  destroyed,  in  any  warm- 
blooded animal,  all  movements  of  respiration  cease  instantaneously. 
The  circulation  still  continues  for  a  time ;  but  as  the  blood  becomes 
deficient  in  aeration,  it  is  gradually  retarded  and  after  several  minutes 
ccmes  to  an  end.  The  effect  of  this  operation  upon  the  two  functions 
of  circulation  and  respiration  is  very  different.  The  circulation  is 


THE     BRAIN.  441 

interfered  with  and  finally  arrested  as  a  secondary  consequence,  because 
the  blood  is  no  longer  arterialized ;  but  respiration  is  abolished  at  once, 
as  an  immediate  result  of  injury  to  the  medulla. 

As  the  movements  of  respiration  are  performed  by  the  consenta- 
neous action  of  different  muscles,  the  effect  of  an  injury  to  the  cerebro- 
spinal  axis  will  vary  according  to  its  locality.  The  respiratory  move- 
ments of  the  chest  and  abdomen  are  arrested  by  section  of  the  cord 
anywhere  above  the  third  cervical  vertebra,  since  this  paralyzes  both 
the  diaphragm  and  the  intercostal  muscles.  But  movements  of  inspi- 
ration, simultaneous  with  those  of  the  chest  and  abdomen,  are  also 
performed  by  the  glottis ;  and  in  most  quadrupeds  there  is  at  the  same 
time  an  expansion  of  the  nostrils,  all  associated  with  each  other  in  the 
act  of  respiration.  If  the  spinal  cord  be  divided  at  the  third  cervical 
vertebra  the  movements  of  the  chest  and  abdomen  cease,  but  those  of 
the  glottis  and  nostrils  continue,  since  the  nerves  supplying  these  parts 
are  still  in  communication  with  the  medulla  oblongata.  But  destruc- 
tion of  the  medulla  arrests  at  the  same  instant  all  movements  of  respi- 
ration, both  in  the  trunk,  the  glottis,  and  the  face. 

The  medulla  accordingly  is  a  centre  from  which  the  whole  respiratory 
apparatus  derives  its  stimulus,  and  in  man,  quadrupeds,  and  birds  it  is 
the  most  important  part  of  the  brain  for  the  immediate  preservation 
of  life. 

The  more  exact  location  of  the  respiratory  centre  was  investigated 
by  Flourens  *  by  making  transverse  sections  of  the  medulla  at  different 
parts  of  its  length,  and  observing  the  effect  produced.  The  result 
showed  that  such  injuries,  inflicted  just  behind  the  point  of  emergence 
of  the  pneumogastric  nerves,  destroyed  all  the  movements  of  respira- 
tion together.  Below  this  point,  the  movements  of  the  chest  and  abdo- 
men were  stopped,  but  those  of  the  nostrils  and  glottis  continued ;  above 
it,  the  movements  of  the  nostrils  were  arrested,  while  those  of  the 
chest  and  abdomen  went  on. 

Flourens  subsequently  f  limited  the  position  of  this  centre  still  more 
closely.  In  rabbits  it  occupies  a  space  of  about  2.5  millimetres  on  each 
side  the  median  line,  situated  at  the  lower  end  of  the  fourth  ventricle, 
a  little  in  advance  of  the  divergence  of  the  posterior  pyramids,  and 
just  at  the  point  of  gray  substance  formed  by  the  ala  cinerea.  A 
section  of  the  medulla  at  this  spot,  with  a  double-edged  knife  only 
5  millimetres  wide,  or  its  perforation  at  the  same  point  with  a  sharp- 
edged  canula  not  more  than  3  millimetres  in  diameter,  caused  imme- 
diate stoppage  of  respiration ;  while  this  effect  was  not  produced  by 
similar  injuries  either  above  or  below.  This  spot,  which  contains  the 
nervous  centre  of  respiration,  corresponds,  in  man,  on  the  front  of  the 
medulla  oblongata,  with  the  upper  end  of  the  decussation  of  the  ante- 

*  Kecherches  Experimentales  sur  les  Proprietes  et  les  Fonctions  du  SystSme  Ner- 
veux.  Paris,  1842,  pp.  196-204. 

f  Comptes  Eendus  de  1' Academic  des  Sciences.     Paris,  1858,  tome  xlvii.,  p.  803. 


442  THE    NERVOUS    SYSTEM. 

rior  pyramids,  or  the  lower  extremity  of  the  olivary  bodies,  and  is  some- 
what below  the  apparent  origin  of  the  pneumogastric  nerves. 

Respiration  accordingly  is  an  act  consisting  of  various  associated 
movements,  which  have  their  nervous  centre  in  the  medulla  oblongata. 
The  movements  themselves  are  involuntary  in  character ;  for  although 
those  of  the  chest  and  abdomen  may  be  for  a  short  time  increased  in 
frequency,  the  surplus  movements  thus  performed  are  not  necessary  to 
respiration,  and  soon  produce  a  fatigue  which  prevents  their  continu- 
ance. Respiration  goes  on  with  its  natural  rhythm,  unaccompanied  by 
fatigue,  under  the  influence  of  the  medulla,  from  the  moment  of  birth, 
without  necessary  consciousness  of  its  existence.  If  arrested  by  vol- 
untary effort,  the  internal  stimulus  which  prompts  it  grows  gradually 
more  urgent,  until  the  will  can  no  longer  withstand  its  demands ;  and 
as  soon  as  voluntary  resistance  is  discontinued,  the  movement  recom- 
mences under  the  independent  action  of  the  medulla  oblongata. 

The  function  of  the  medulla  in  respiration  is  usually  regarded  as  a 
reflex  act.  According  to  this  view,  its  gray  substance  is  sensitive  to 
a  stimulus  derived  from  the  lungs  and  other  vascular  organs,  which 
gives  notice  of  a  commencing  deficiency  in  respiration.  This  excites 
in  the  medulla  a  motor  impulse,  which  is  reflected  in  the  centrifugal 
direction  and  calls  into  activity  the  respiratory  muscles.  In  normal 
respiration  the  reflex  action  of  the  medulla  takes  place  without  an 
appreciable  sensation.  On  the  renewal  of  air  in  the  lungs  by  inspira- 
tion, the  unconscious  demand  is  satisfied,  the  muscles  relax,  and  expi- 
ration follows  by  passive  collapse  of  the  lungs  and  thorax.  In  a  few 
seconds,  as  the  oxygen  is  consumed  and  carbonic  acid  accumulates,  the 
previous  condition  recurs  and  the  action  is  repeated  as  before,  thus 
causing  the  rhythmical  alternating  movements  of  inspiration  and  expi- 
ration. 

The  evidence  that  the  medulla  acts  in  this  way  as  a  reflex  centre  for 
respiration  is  mainly  of  two  kinds.  First,  the  sudden  contact  of  an 
external  stimulus,  such  as  a  dash  of  cold  water  on  the  skin,  or  the  appli- 
cation of  a  pungent  vapor  to  the  nostrils,  causes  almost  invariably  an 
involuntary  inspiration.  As  the  medulla  is  the  sole  nervous  centre  for 
respiratory  movements,  the  external  impression  in  these  cases  must  be 
conveyed  by  centripetal  fibres  to  its  gray  substance,  exciting  there  the 
special  motor  stimulus  of  respiration.  Secondly,  division  of  the  pneu- 
mogastric nerve,  an  operation  which  shuts  off  from  the  medulla  all 
influences  derived  from  the  lungs,  causes  immediate  diminution  in  the 
frequency  of  respiration  ;  a  result  which  may  be  explained  by  supposing 
that  the  most  effective  stimulus  to  the  medulla  as  a  respiratory  centre 
is  received  from  the  lungs  through  this  nerve. 

A  different  view  of  the  action  of  the  medulla  in  respiration  is  taken 
by  Foster  *  and  by  Flint,  f  According  to  these  writers,  the  medulla 

*  Text-book  of  Physiology.     London,  1879,  p.  334. 

f  American  Journal  of  the  Medical  Sciences.  Philadelphia,  1880,  vol.  Ixxx.,  p.  69. 


THE    BRAIN.  443 

generates  within  itself  the  nervous  stimulus  to  respiration,  indepen- 
dently of  external  impressions.  The  immediate  cause  of  its  action  is 
attributed  by  Flint  to  a  deficiency  of  oxygenated  blood  in  its  capillary 
vessels,  by  which  it  is  excited  to  momentary  activity.  The  author  sus- 
tains this  view  by  the  result  of  experiments  on  animals,  in  which  invol- 
untary movements  of  respiration  were  excited  by  cutting  off  the  supply 
of  arterial  blood  from  the  medulla  and  other  parts  of  the  encephalon. 
But  both  these  authors  agree  in  considering  the  medulla  as  in  some 
way  the  indispensable  nervous  centre  for  respiration. 

An  irregularity  in  the  movements  of  respiration  is,  accordingly,  one 
of  the  most  threatening  symptoms  in  affections  of  the  brain.  Cerebral 
apoplexy  at  the  surface  of  the  hemispheres,  in  the  lateral  ventricles,  or 
in  the  cerebral  ganglia,  is  seldom  immediately  fatal,  however  extensive 
the  injury.  But  when  occurring  in  the  medulla  oblongata  or  its  im- 
mediate neighborhood,  it  produces  death  instantaneously  by  the  same 
mechanism  as  where  this  part  is  destroyed  by  experiment  in  animals. 
When  the  medulla  is  implicated,  in  man,  by  progressive  disease  or  by 
failure  of  its  nervous  functions,  the  respiratory  movements  first  affected 
are  those  of  the  face,  while  those  of  the  chest  and  abdomen  go  on  for  a. 
time  as  usual.  The  cheeks  are  drawn  in  with  every  inspiration  and 
puffed  out  with  every  expiration,  the  nostrils  sometimes  participating 
in  these  abnormal  movements.  A  still  more  dangerous  symptom,  which 
frequently  precedes  death,  is  an  irregular  and  hesitating  respiration, 
usually  noticeable  after  the  remaining  cerebral  functions  have  been 
already  impaired.  These  phenomena  depend  on  the  connection  between 
respiration  and  the  medulla  as  a  nervous  centre. 

Deglutition  is  also  under  the  control  of  the  medulla.  Mastication 
of  the  food,  and  its  transfer  by  the  tongue  to  the  entrance  of  the  fauces, 
are  voluntary  actions,  which  may  be  continued  or  arrested  at  will.  But 
when  the  food  has  passed  from  the  mouth  into  the  pharynx,  the  pro- 
cess of  deglutition,  by  which  it  is  carried  down  into  the  stomach,  is 
reflex  and  involuntary.  Once  commenced,  it  cannot  be  arrested  by 
the  will,  as  it  consists  of  muscular  contractions  following  each  other  in 
undeviating  succession,  and  receiving  their  impulse  from  the  medulla 
oblongata.  In  the  experiments  of  Flourens  and  Longet,  fowls  and 
pigeons,  after  removal  of  the  cerebral  hemispheres,  never  picked  up 
their  food  spontaneously,  nor  even  swallowed  it  when  placed  in  the 
mouth  at  the  end  of  the  beak ;  but  if  carried  backward  into  the  pharynx, 
it  was  at  once  embraced  by  the  muscular  walls  of  this  organ,  and  car- 
ried into  the  stomach  by  a  continuous  movement  of  deglutition.  This 
movement  includes,  not  only  the  associated  contraction  of  the  pharynx 
and  oesophagus,  but  also  the  stoppage  of  respiration  and  closure  of  the 
glottis,  by  which  the  food  is  prevented  from  passing  into  the  larynx. 
According  to  Vulpian,  after  all  parts  of  the  brain  have  been  removed, 
in  cats  or  guinea-pigs,  excepting  the  medulla,  swallowing  may  still  be 
accomplished  by  reflex  action ;  but  it  becomes  impossible  as  soon  as 
this  part  is  removed  or  seriously  injured.  The  necessary  muscular 


444  THE    NERVOUS    SYSTEM. 

combinations   cannot  take   place,  except   under   the   influence  of  the 
medulla  as  a  nervous  centre. 

Deglutition  may  consequently  be  performed,  in  man,  after  conscious 
sensibility  and  voluntary  power  have  disappeared.  In  compression  of 
the  brain  from  injury  or  disease,  when  the  individual  is  completely 
unconscious,  and  even  when  respiration  has  become  diminished  in 
frequency,  solid  or  liquid  food,  if  carried  into  the  upper  part  of  the 
pharynx,  may  be  successfully  swallowed  by  the  ordinary  movements. 
When  this  process  is  no  longer  possible,  or  is  accompanied  by  choking 
or  regurgitation,  it  indicates  that  the  medulla  has  become  seriously 
affected,  and  that  death  is  probably  near  at  hand. 

The  medulla  is  furthermore  connected  with  phonation.  A  vocal 
sound  is  usually  caused  by  a  voluntary  impulse  from  the  cerebral 
hemispheres.  It  may  also  be  a  purely  emotional  act,  without  any 
reasonable  or  intelligent  motive.  But  in  both  cases  its  actual  pro- 
duction is  a  secondary  result,  requiring  special  nervous  combinations, 
the  immediate  centre  of  which  is  located  in  the  medulla.  This  is 
shown  by  the  fact  that  a  cry  may  still  be  produced,  under  an  irrita- 
tion applied  to  the  medulla,  when  the  upper  parts  of  the  encephalon 
have  been  removed.  If  a  stilet  be  introduced  into  the  cranium  of  a 
frog,  the  cerebral  hemispheres  may  be  broken  up  without  producing 
any  excitement  of  the  vocal  organs;  but  the  contact  of  the  instru- 
ment with  the  medulla  is  often  followed  by  a  spasmodic  cry.  Yulpian 
has  shown  that  a  similar  effect  may  be  produced  in  mammalians  by 
reflex  action,  after  removal  of  the  whole  encephalon  excepting  the 
medulla ;  a  cry  being  produced  each  time  the  foot  is  pinched  by  a  for- 
ceps. This  sound,  however,  gives  no  indication  of  consciousness  or 
sensibility  on  the  part  of  the  animal.  It  is  short,  abrupt,  and  moment- 
ary, and  is  repeated  only  when  the  irritation  is  again  applied  to  the 
external  parts.  After  destruction  of  the  medulla,  on  the  other  hand, 
no  vocal  sound  can  be  produced,  and  irritation  of  the  integument  is 
followed  only  by  the  ordinary  movement  of  the  limbs,  dependent  on 
reflex  action  of  the  spinal  cord. 

In  the  exercise  of  the  voice,  therefore,  the  preliminary  actions  of 
intelligence,  volition,  or  emotional  excitement  require  the  cooperation 
of  other  parts  of  the  encephalon ;  but  the  immediate  mechanism  by 
which  a  vocal  sound  is  produced  has  its  nervous  centre  in  the  medulla 
oblongata. 

The  medulla  oblongata,  with  the  adjoining  part  of  the  tuber  annu- 
lare,  is  also  the  direct  source  of  the  movements  of  articulation.  It  is 
the  gray  substance  of  this  region  that  gives  origin  to  the  hypoglossal 
and  facial  nerves  distributed  to  the  muscles  of  the  tongue  and  lips,  and 
to  the  motor  fibres  of  the  pneumogastric  nerve,  which  regulate  the 
condition  of  the  rima  glottidis.  Disease  or  injury  in  this  situation, 
sufficient  to  impair  nervous  action,  consequently  makes  articulation 
difficult  or  impossible.  This  affection  is  quite  distinct  from  "aphasia," 
which  is  of  cerebral  origin,  and  in  which  the  external  mechanism  of 


THE    BRAIN.  445 

speech  is  unaffected,  the  muscles  of  the  tongue  and  lips  retaining  their 
normal  power  of  movement.  In  disease  of  the  medulla,  on  the  other 
hand,  the  muscular  paralysis  is  very  evident,  and  is  mainly  confined 
to  the  muscles  of  articulation  and  phonation. 

Such  a  disease  is  that  known  as  glosso-labio-laryngeal  paralysis. 
It  is  a  paralysis  due  to  chronic  degeneration  of  the  gray  substance  in 
the  medulla  oblongata,  and  affects  the  motor  nerves  of  the  tongue,  the 
face,  the  hanging  palate,  and  the  larynx.  The  first  difficulty  is  gen- 
erally noticeable  in  the  movements  of  the  tongue,  which  cannot  be 
applied  accurately  to  the  teeth  or  the  roof  of  the  mouth ;  the  lingual 
and  dental  consonants  being  therefore  pronounced  imperfectly  or  not 
at  all.  The  lips  are  next  affected,  so  that  they  cannot  be  brought  in 
contact  with  each  other,  and  B  and  P  are  pronounced  like  V  or  F. 
As  the  debility  of  the  orbicularis  oris  increases,  entirely  preventing 
approximation  of  the  lips,  the  vowels  O  and  U  are  no  longer  sounded ; 
and,  by  the  continued  exaggeration  of  these  difficulties,  the  patient's 
speech  becomes  at  last  unintelligible.  Deglutition  is  also  affected,  and 
the  attempt  to  swallow  is  liable  to  cause  choking  from  imperfect  pro- 
tection of  the  rima  glottidis.  Phonation  becomes  impaired  from  debility 
of  the  laryngeal  muscles,  and  in  advanced  cases  no  vocal  sound  can  be 
produced.  The  disease  is  uniformly  progressive,  and  usually  termi- 
nates by  affecting  the  movements  of  respiration. 

The  medulla  oblongata  is,  accordingly,  the  seat  of  reflex  actions  con- 
nected with  the  immediate  preservation  of  life,  since  it  maintains  the 
movements  by  which  air  and  food  are  introduced  into  the  body.  It 
also  presides  over  the  muscular  combinations  concerned  in  the  voice 
and  articulation,  and  by  this  means  establishes  an  intelligible  commu- 
nication with  the  external  world. 


CHAPTER    VI. 
THE    CRANIAL  NERVES. 

THE  cranial  nerves,  which  take  their  origin  from  the  base  of  the 
brain,  are  in  great  measure  analogous  in  anatomical  and  physio- 
logical character,  with  the  spinal  nerves.  An  exception  to  this  rule 
exists  only  in  the  three  nerves  of  special  sense,  the  olfactory,  optic,  and 
auditory,  which  are  endowed  neither  with  tactile  sensibility  nor  motor 
power,  and  which  are  connected  in  a  special  way  with  the  gray  sub- 
stance of  the  hemispheres. 

The  remaining  cranial  nerves  are  distributed  either  to  the  integu- 
ment, mucous  membranes,  or  muscular  tissues,  and  are  either  sensitive 
or  motor,  or  have  both  properties  combined.  Some  of  them,  like  the 
oculomotorius,  the  patheticus,  and  the  facial,  are  distinctively  motor 
in  character,  are  distributed  to  muscles,  produce  convulsive  motion  on 
being  irritated,  and,  when  injured  or  divided,  leave  the  corresponding 
parts  in  a  state  of  paralysis.  Others,  such  as  the  trigeminus,  the 
glosso-pharyngeal,  and  the  pneumogastric,  are  sensitive  nerves,  pos- 
sessing either  an  acute  tactile  sensibility,  like  the  trigeminus,  or  one 
of  more  special  nature,  like  the  glosso-pharyngeal  and  pneumogastric. 
Like  the  posterior  roots  of  the  spinal  nerves,  they  are  provided  with  a 
ganglion  near  their  points  of  emergence  from  the  base  of  the  brain ; 
and  they  are  distributed  either  to  the  integument  or  mucous  mem- 
branes or  to  both. 

The  anatomical  similarity  between  the  cranial  and  spinal  nerves  is 
in  some  instances  very  marked.  The  fifth  pair,  or  trigeminus,  emerges 
from  the  tuber  annulare  by  two  roots,  of  which  one  is  sensitive,  the 
other  motor;  the  sensitive  root  presenting  a  well  developed  ganglion, 
with  which  the  fibres  of  the  motor  root  do  not  mingle.  Beyond  the 
ganglion,  accordingly,  the  nerve  contains  both  motor  and  sensitive 
fibres,  and  is  distributed  both  to  muscles  and  to  the  integument.  The 
glosso-pharyngeal  nerve  is  joined,  beyond  its  ganglion,  by  motor  fibres 
from  the  facial ;  and  the  pneumogastric  receives  communications  from 
the  spinal  accessory  and  other  motor  nerves.  Both  sensibility  and 
motion  are  therefore  provided  for,  in  a  manner  not  essentially  dif- 
ferent, by  the  cranial  and  spinal  nerves. 

The  other  points,  both  of  difference  and  analogy,  in  the  cranial 
nerves,  relate  to  their  origin  and  distribution.  Their  apparent  origin, 
or  the  point  at  which  they  become  detached  from  the  surface  of  the 
brain,  is  not  their  real  origin ;  but  in  every  case  their  fibres  can  be 
traced  inward,  often  for  a  considerable  distance,  between  the  tracts  of 
white  substance,  until  they  reach  a  central  mass  of  gray  matter  from 

446 


THE    CRANIAL    NERVES. 


447 


which  they  originate,  and  which  is  called  their  "  nucleus."  For  all 
except  the  olfactory  and  optic  nerves,  these  nuclei  of  origin  are  situ- 
ated along  the  floor  of  the  fourth  ventricle  or  about  the  aqueduct  of 
Sylvius. 

The  peculiarities  of  peripheral  distribution,  in  the  cranial  nerves,  are 
more  apparent  than  real  in  importance.  The  oculomotorius,  patheti- 
cus,  and  abducens  emerge  from  the  brain  at  very  different  points,  and, 
running  forward  through  the  cranial  cavity  in  the  form  of  separate 
cords,  are  enumerated  as  three  nerves.  But  they  all  originate  from 
the  same  layer  of  gray  substance,  two  of  them,  the  oculomotorius  and 
the  patheticus,  in  close  proximity  to  each  other ;  they  all  pass  from 
the  cranial  into  the  orbital  cavity  by  the  sphenoidal  fissure  ;  and  they 
are  all  distributed  to  muscles  moving  the  eyeball.  In  a  physiological 
point  of  view,  therefore,  they  are  branches  of  a  single  nerve.  Even 
when  two  or  more  nerves  emerge  from  the  cranium  by  different  foram- 
ina, like  the  three  divisions  of  the  trigeminus,  they  are  nevertheless, 
properly  speaking,  parts  of  the  same  nerve,  if  they  have  similar  physi- 
ological properties  and  are  distributed  to  the  same  region.  It  is  the 
character  and  ultimate  destination  of  a  nerve,  and  not  its  course 
through  the  bones  of  the  skull,  which  determine  its  physiological 
position.  In  the  bull-frog,  as  shown  by  Wyman,*  both  the  facial 
nerve  and  the  abducens  are  given  off  as  branches  from  the  fifth  pair ; 
and  in  most  quadrupeds,  the  frontal  branches  of  the  ophthalmic  divi- 
sion of  the  trigeminus  are  nearly  wanting,  in  accordance  with  the 
imperfect  sensibility  of  the  forehead  and  vertex. 

The  cranial  nerves  may,  therefore,  be  conveniently  arranged  in  pairs 
according  to  their  distribution  and  functions,  notwithstanding  the  inci- 
dental peculiarities  of  their  course  or  subdivision.  The  olfactory,  optic, 
and  auditory  nerves  form  a  separate  specific  group ;  while  the  remain- 
der consist  of  motor  and  sensitive  nerves,  supplying  the  muscles  and 
integument  of  different  regions. 

CRANIAL  NERVES. 


Nerves  of  Special  Sense. 
1.  Olfactory.     2.  Optic.     3.  Auditory. 


1st  PAIR. 


2d  PAIR. 
3d  PAIR. 


Motor  nerves. 
Oculomotorius 
Patheticus 
Abducens 
Facial 

Small  root  of  5th  pair 
Hypoglossal 
Spinal  accessory 


Sensitive  nerves. 


Distributed  to  the 


Trigeminus. 


Glosso-pharyngeal. 
Pneumogastric. 


Upper,    middle,    and 
lower  facial  regions. 

Tongue  and  pharynx. 
Passages  of   respira- 
tion and  deglutition. 


This  division  of  the  cranial  nerves,  according  to  their  physiological 
character,  is  not  perfect  in  all  particulars.     For  while  the  hypoglossal 


Nervous  Systems  of  Kana  pipiens.    Smithsonian  Institution  ;  Washington,  1853. 


448  THE    NERVOUS    SYSTEM. 

nerve  supplies  only  the  muscles  of  the  tongue,  its  associate,  the  glosso- 
pharyngeal,  sends  part  of  its  sensitive  fibres  to  the  tongue  and  part 
to  the  pharynx ;  and  while  the  trigeminal  nerve  is  mainly  distributed 
to  the  external  parts  of  the  face,  one  of  its  deeper  branches,  the  lingual, 
is  distributed  to  the  tongue.  The  arrangement,  however,  is  substan- 
tially correct,  and  may  serve  as  a  useful  guide  in  the  study  of  the 
nervous  functions. 

First  Pair.    The  Olfactory  Nerves. 

What  is  called  in  man  the  "olfactory  nerve,"  is  a  prismatic  extension 
of  gray  and  white  substance,  running  in  a  longitudinal  groove  on  the 
under  surface  of  the  anterior  cerebral  lobe,  near  the  median  line,  arid 
terminating  anteriorly  in  a  flattened  ovoid  mass  of  gray  substance,  the 
"olfactory  bulb."  The  olfactory  bulb  rests  upon  the  cribriform  plate 
of  the  ethmoid  bone,  and  gives  off,  through  the  perforations  in  this 
bone,  the  nervous  filaments  supplying  the  olfactory  membrane  in  the 
nasal  passages.  The  prismatic  mass  connecting  the  olfactory  bulb  with 
the  rest  of  the  brain  is,  in  reality,  an  extension  of  the  anterior  lobe,  and 
forms  part  of  the  cerebral  convolutions.  In  most  quadrupeds  it  is 
much  larger  than  in  man,  often  enclosing  a  prolongation  of  the  lateral 
ventricle ;  and  in  size  and  structure  it  exhibits  so  close  a  resemblance 
with  the  remaining  convoluted  portion  of  the  brain,  that  it  is  properly 
designated  as  the  "  olfactory  lobe."  In  man  it  is  so  slightly  developed 
that  this  term  can  hardly  be  applied  to  it ;  but  it  nevertheless  consists 
partly  of  gray  substance,  and  shows  only  on  its  superficial  border  a 
longitudinal  striation  of  white  substance,  which  connects  the  olfactory 
bulb  in  front  with  the  central  parts  of  the  brain  behind. 

The  olfactory  apparatus  consists  accordingly  of,  1st,  the  olfactory 
nerves  proper,  distributed  upon  the  mucous  membrane  of  the  upper 
part  of  the  nasal  passages,  and  connected  at  their  central  extrem- 
ity with  the  gray  substance  of  the  olfactory  bulb ;  2d,  the  olfactory 
bulbs,  situated  on  the  anterior  extremity  of  the  olfactory  lobes,  and 
giving  origin,  as  above  described,  to  the  nerves  of  the  olfactory  mem- 
brane ;  and  3d,  the  olfactory  tracts,  that  is  the  longitudinal  bands 
of  white  substance,  running  along  the  superficial  border  of  the  olfac- 
tory lobes  (commonly  called  "  olfactory  nerves  "),  toward  the  central 
parts  at  the  base  of  the  brain. 

Physiological  Properties  of  the  Olfactory  Nerve. — The  connection 
of  the  olfactory  nerve  with  the  sense  of  smell  is  indicated  by,  1st,  its 
anatomical  relations ;  2d,  its  comparative  development  in  different  ani- 
mals ;  and  3d,  the  results  of  its  injury  or  disease. 

I.  The  only  anatomical  connection  of  the  olfactory  tracts,  at  their 
anterior  extremity,  is  with  the  olfactory  bulb ;  and  the  nerve  fibres 
given  off  from  this  part  are  distributed  only  to  the  olfactory  region 
of  the   nasal  passages.      In  this   region   ordinary  sensibility  is  but 
slightly  developed,  while  it  is  highly  endowed  with  the  sense  of  smell. 

II.  In  animals  possessing  a  more  acute  sense  of  smell  than  man,  like 


THE    CRANIAL    NERVES.  449 

the  dog,  cat,  sheep,  and  most  other  quadrupeds,  both  the  olfactory 
bulbs  and  the  olfactory  tracts  are  increased  in  a  similar  ratio.  There 
is  accordingly  a  direct  correspondence  between  their  development  and 
that  of  the  special  sense  with  which  they  are  connected. 

III.  A  number  of  cases  are  quoted  by  Longet  in  which  congenital 
absence  of  the  olfactory  nerves,  in  man,  was  accompanied  by  congenital 
incapacity  to  distinguish  odors ;  and  others  in  which  loss  of  smell  was 
observed  after  affections  causing  their  compression  or  destruction. 

Finally,  experimental  division  or  destruction  of  these  nerves  in  dogs 
abolishes,  so  far  as  observation  can  show,  the  power  of  discriminating 
odors;  although  it  leaves  the  nasal  mucous  membrane  sensitive  to 
pungent  or  caustic  vapors.  In  the  experiments  of  Magendie,*  a  dog, 
after  destruction  of  both  olfactory  nerves,  would  disentangle  a  package 
containing  meat  when  openly  presented  to  him;  but  he  did  not  find  it, 
when  placed  near  by  without  his  knowledge.  The  same  result  was 
obtained  by  Vulpian  f  in  experiments  upon  hunting  dogs.  These  ani- 
mals, after  recovering  from  the  immediate  effects  of  the  operation, 
were  kept  fasting  for  two  days,  and  then  introduced  into  an  apart- 
ment where  a  piece  of  cooked  meat  was  concealed ;  but  they  were 
never  able  to  discover  it,  when  the  division  of  the  nerves  had  been 
complete.  Notwithstanding,  therefore,  the  difficulty  of  experimenting 
upon  so  obscure  a  function  as  that  of  smell,  there  is  no  doubt  that  the 
olfactory  nerves  and  bulbs  are  the  internal  organs  of  the  olfactory 
sense,  and  that  they  are  disconnected  both  with  ordinary  sensibility  and 
the  power  of  motion. 

Second  Pair,    The  Optic  Nerves. 

The  optic  nerves  are  distinguished  by  their  very  prominent  decussa- 
tion  at  the  base  of  the  brain,  where  they  present  the  appearance  of 
being  consolidated  with  each  other.  By  this  decussation,  which  is 
called  the  "  chiasma,  "J  they  are  divided  into  two  portions.  The  optic 
nerves  proper,  situated  in  front  of  the  chiasma,  are  nearly  cylindrical 
in  form  and  consist  of  fibres  coming  directly  from  the  retina  on  each 
side.  Behind  the  chiasma  they  are  known  as  the  "optic tracts,"  and 
appear  as  flattened  bands  of  nerve  fibres,  connecting  the  visual  organs 
with  the  central  parts  of  the  brain.  The  optic  tract  on  each  side,  after 
following  the  contour  of  the  crus  cerebri  in  a  backward  direction,  divides 
into  two  roots,  an  internal  and  an  external.  The  internal  root  is  con- 
nected with  the  corpus  geniculatum  internum,  through  and  over  which 
its  fibres  pass,  continuing  their  course  upward  and  backward  until  they 
reach  the  anterior  tubercula  quadrigemina.  The  external  root,  which 
is  the  larger  of  the  two,  is  attached  to  the  corpus  geniculatum  externum. 

*  Journal  de  Physiologic  Experimental  et  Pathologique.  Paris,  1825,  tome  iv., 
p.  170. 

f  Le9ons  sur  la  Physiologic  du  Systeme  Nerveux.     Paris,  1866,  p.  882. 

J  This  term  is  of  Greek  origin,  and  is  derived  from  a  verb  which  signifies  to  mark 
with  the  letter  x. 

2D 


450  THE    NERVOUS    SYSTEM. 

Here  some  of  its  fibres  are  connected  with  the  gray  substance  of  this 
ganglion ;  while  others  pass  onward  to  their  termination  in  the  poste- 
rior part  of  the  optic  thalamus.  This  represents  the  central  connec- 
tion of  the  optic  tracts,  as  described  by  Wagner,  Henle,  and  Huguenin, 
and  as  generally  accepted  by  modern  anatomists.  The  optic  tracts  have 
accordingly  their  origin  in  three  separate  nuclei  or  deposits  of  gray 
substance,  namely,  1st,  the  anterior  tubercula  quadrigemina ;  2d,  the 
corpus  geniculatum  externum ;  and  3d,  the  optic  thalamus. 

But  there  are,  beyond  question,  further  indirect  connections  between 
these  nuclei  and  the  cortex  of  the  hemispheres.  They  consist  of  diverg- 
ing fibres  from  both  the  optic  thalamus  and  the  corpora  geniculata, 
which,  according  to  Gratiolet,  Meynert,  and  Huguenin,*  take  part  in 
the  formation  of  the  corona  radiata  and  pursue  their  course  toward  the 
posterior  part  of  the  hemispheres. 

Physiological  Properties  of  the  Optic  Nerves. — The  optic  nerves 
are  nerves  of  special  sense,  and  may  be  regarded  as  tracts  of  fibres 
connecting  the  gray  matter  of  the  cerebrum  with  the  retinal  expansion 
in  the  eyeball.  They  are  destitute  of  tactile  sensibility  and  convey 
inward  only  the  impression  caused  by  luminous  rays.  In  the  central 
parts  of  the  brain  this  impression  produces  the  sensation  of  light ;  and 
the  optic  nerves  are  therefore  the  channels  for  the  sense  of  vision. 
Magendie  found  in  quadrupeds  both  the  retina  and  the  optic  nerves 
throughout  their  length  insensible  to  mechanical  irritation ;  and,  in 
man,  touching  the  retina  with  a  cataract  needle  excited  no  perceptible 
sensation.  It  has  also  been  remarked,  in  cases  of  extirpation  of  the 
eyeball,  that  section  of  the  optic  nerve  is  not  painful ;  and,  according 
to  Longet,  these  nerves  in  the  lower  animals  may  be  pinched,  pricked, 
cauterized,  divided,  or  injured  in  various  ways  without  causing  signs 
of  pain. 

On  the  other  hand,  their  division  at  once  produces  blindness.  The 
impressions  received  by  the  retina  are  no  longer  transmitted  to  the 
central  organ,  and  the  animal  becomes  insensible  to  light,  without  any 
loss  of  tactile  sensibility  or  the  power  of  motion. 

Beside  their  immediate  function  in  the  perception  of  light,  the  optic 
nerves  are  the  channels  for  a  special  reflex  action  ;  namely,  that  of  the 
contractile  movements  of  the  iris. 

These  movements,  by  which  the  quantity  of  light  admitted  to  the  eye 
is  regulated  by  the  size  of  the  pupil,  are  involuntary  in  character,  but 
are  due  to  impressions  conveyed  inward  by  the  optic  nerve.  The  im- 
pression, first  received  upon  the  retina,  passes  through  the  optic  nerve 
to  the  tubercula  quadrigemina.  Its  transformation  into  a  motor  impulse 
is  either  accomplished  in  these  bodies,  or  is  commenced  in  them  and 
completed  by  transmission  to  the  nucleus  of  origin  of  the  oculomotorius 
nerves.  Thus  both  the  optic  nerves  and  the  tubercula  quadrigemina 
are  essential  to  the  movements  of  the  pupil  under  the  influence  of  light. 


*  Anatomic  des  Centres  Nerveux.     Paris,  1879,  pp.  Ill,  135. 


THE    CRANIAL    NERVES. 


451 


That  this  is  a  reflex  action  is  shown  by  dividing  and  irritating  the 
optic  nerves.  After  section  of  the  nerve,  according  to  the  experiments 
of  Mayo  and  Longet,  upon  pigeons,  dogs,  and  rabbits,  irritation  of  its 
peripheral  end,  that  is,  the  portion  still  connected  with  the  eyeball, 
produces  no  effect  on  the  pupil ;  but  irritation  of  its  central  portion, 
which  is  connected  with  the  brain,  at  once  causes  contraction.  On  the 
other  hand,  division  of  the  oculomotorius  nerve  paralyzes  the  iris  and 
puts  an  end  to  the  movements  of  the  pupil,  although  the  eye  may  be 
otherwise  uninjured  and  the  perception  of  light  unimpaired. 

Decussation  of  the  Optic  Nerves. — The  decussation  of  the  optic 
nerves,  which  in  man  and  all  vertebrate  animals  is  visible  on  super- 
ficial examination,  varies  considerably  in  its  details  in  different  classes. 
These  variations  may  be  mainly  referred  to  three  distinct  types,  gen- 
erally known  to  comparative  anatomists,  and  more  distinctly  recog- 
nized in  the  recent  investigations  of  Nicati.* 


FIG.  119. 


FIG.  120. 


INFERIOR  SURFACE  OF  THE  BRAIN  OF  THE 
COD.— 1.  Optic  nerve  of  right  eye.  2.  Optic 
nerve  of  left  eye.  3.  Right  optic  tubercle. 
4.  Left  optic  tubercle.  5,  6.  Cerebral  hemi- 
spheres. 7.  Medulla  oblongata. 


INFERIOR  SURFACE  OF  THE  BRAIN  OF  FOWL. 
— 1.  Optic  nerve  of  right  eye.  2.  Optic  nerve 
of  left  eye.  3.  Right  optic  tubercle.  4.  Left 
optic  tubercle.  5,  6.  Cerebral  hemispheres. 
7.  Medulla  oblongata. 


I.  In  fishes  and  reptiles  the  optic  nerves  cross  each  other  without  com- 
mingling, so  that  their  complete  decussation  is  visible  to  the  unaided 
eye.  In  many  instances,  as  in  the  cod  (Fig.  119),  each  nerve,  preserv- 
ing its  cylindrical  form,  passes  either  above  or  below  its  fellow  to  the 
eye  of  the  opposite  side.  In  others,  as  in  the  herring,  the  nerve  of  the 
right  side  passes  through  a  slit  or  fenestra  in  that  of  the  left ;  and  in 
others  still,  the  decussation  takes  place  by  several  distinct  bundles  of 
fibres  crossing  at  various  levels  above  or  below  each  other.  Through- 
out these  two  classes  it  is  plainly  evident  that  all  the  optic  fibres  com- 


Archives  de  Physiologie.     Paris,  1878,  2me  serie,  tonie  v.,  p.  658. 


•452  THE    NERVOUS    SYSTEM. 

ing  from  one  side  of  the  brain  go  to  the  eye  of  the  opposite  side,  and 
vice  versa. 

II.  In  birds  the  optic  nerves  appear  superficially  to  be  united  at  the 
chiasma,  but  dissection  shows  that  they  are  only  broken  up  into  fascic- 
uli of  fibres  which,  though  interwoven  with  each  other,  remain  anatom- 
ically distinct  (Fig.  120).     The  fasciculi  of  each  nerve,  generally  eight 
in  number,  cross  the  median  line  at  the  point  of  decussation,  so  that 
the  retina  of  each  eye  is  exclusively  supplied  with  nerve  fibres  from  the 
opposite  side  of  the  brain.     Experiment  furthermore  shows  that  in  the 
pigeon,  removal  of  the  optic  tubercle  on  one  side  produces  complete 
blindness  in  the  opposite  eye. 

III.  In  the  mammalia,  a»d  in  man,  the  two  optic  nerves  are  so  inti- 
mately consolidated  at  the  chiasma,  that  the  course  of  their  respective 
fibres  cannot  be  determined  by  simple  inspection,  nor  by  the  ordinary 
means  of  dissection,  but  requires  the  aid  of  hardening  fluids  and  micro- 
scopic sections.     These  methods  demonstrate  that  in  all  cases  there  is 
a  decussation  at  the  median  line.    According  to  Henle,  the  decussating 
fibres,  in  man,  are  arranged  in  laminas,  about  -fa  of  a  millimetre  in 
thickness,  which  cross  above  and  below  each  other  from  side  to  side ; 
while  in  front  and  behind  the  chiasma  sections  of  the  optic  nerves  and 
tracts  present  only  the  appearance  of  longitudinal  fibres.    All  anatomists 
are  agreed  that  the  greater  part  of  the  optic  fibres  decussate  in  this  way 
at  the  chiasma.     But  the  majority  also  admit  that  this  decussation,  in 
man  and  most  quadrupeds,  is  incomplete  ;  a  portion  of  the  fibres  of  each 
tract,  situated  upon  its  outer  border,  passing  to  the  eye  of  the  same  side, 
while  the  remainder  cross  at  the  chiasma,  to  the  eye  of  the  opposite 
side.     Each  eye  is  supplied,  according  to  this  view,  with  nerve  fibres 
from  the  opposite  optic  tract  and  opposite  side  of  the  brain,  and  also 
with  fibres  from  the  optic  tract  and  the  brain  on  its  own  side.     There 
is,  furthermore,  a  transverse  band  of  fibres,  admitted  by  all  modern 
writers,  passing  across,  at  the  posterior  border  of  the  chiasma,  from 
one  optic  tract  to  the  other.    This  band  is  the  only  part  of  the  chiasma 
which  remains  intact  after  destruction  of  both  eyeballs  and  consequent 
atrophy  of  the  optic  nerves  and  tracts.    It  is  considered  as  a  transverse 
commissure  between  corresponding  parts  of  the  brain,  and  as  having 
no  direct  connection  with  the  sense  of  vision.     The  partial  decussation 
of  the  optic  nerve,  in  man  and  the  higher  quadrupeds,  is  regarded  by 
many,  and  especially  by  Henle,*  as  demonstrated  on  anatomical  groin  ids. 
The  possibility  of  this  is  denied  by  others ;  and  the  existence  of  direct 
fibres,  in  addition  to  those  which  decussate,  is  no  doubi  laruvly  inferred 
from  the  partial  disturbance  of  vision  in  patholo.iriml  cases,  and  from 
the  results  of  physiological  experiment.     In  birds,  as  above  stated, 
the   complete    decussation   of    the    optic    nerves    at   the   chiasma    i.s 
demonstrable  by  dissection;  and  removal  of  one  optic  tubercle  cau-rs 
absolute  blindness  on  the  opposite  side  without  perceptible  loss  of  siulit 

*  llaiulbiu-li  tier  Nervenlehrc  ties  Mensclieii.     IJnuuischweig,  1879,  p.  389. 


THE    CRANIAL    NERVES. 


453 


FIG.  121. 


on  the  same  side.  If  the  decussation  were  also  complete  in  quadru- 
peds, a  longitudinal  section  of  the  chiasma  at  the  median  line  would 
divide  at  once  all  the  optic  nerve 
fibres,  and  produce  blindness  of 
both  eyes.  Bat  Nicati*  has 
shown,  by  experiments  on  cats, 
that  after  such  a  section  vision 
still  exists  in  these  animals  in 
an  unmistakable  degree ;  show- 
ing that  the  eyes  recei  ve  through 
the  optic  nerves  some  fibres 
which  have  not  crossed  the 
median  line.  From  a  compari- 
son of  the  form  and  section  sur- 
faces of  the  optic  tracts  and 
chiasma,  he  finds  that  the  same 
conclusion  is  applicable  to  man. 
Disturbances  of  Vision  from 
Lesion  of  the  Optic  Nerves  or 
Tracts. — There  are  certain  va- 
rieties of  partial  or  complete 
blindness  in  one  or  both  eyes, 
occurring  in  man,  which  are 
only  explainable  on  the  suppo- 
sition of  incomplete  decussa- 
tion of  the  Optic  nerves.  They  DIAGRAM  OF  THE  OPTIC  NERVES  AND  TRACTS,  in  Man. 

J      — 1.  Left  eyeball.    2.  Eight  eyeball.    3,  3.  Corpora 
depend    On    lesion   Or    COmpreS-     geniculata  intema.  4, 4.  Corpora  geniculata  externa. 


5.  Tubercula  quadrigemina.  6, 6.  Centres  of  vision  in 
the  cerebral  hemispheres. 


sion  of  the  optic  fibres  at  differ- 
ent parts  of  their  course.  Com- 
plete blindness  of  one  eye  is  produced  by  a  lesion  involving  the  whole 
of  one  optic  nerve,  between  the  chiasma  and  the  eyeball,  as  at  A,  Fig. 
122 ;  since  such  an  injury  interrupts  all  the  nerve  fibres,  from  whatever 
source,  going  to  the  retina  of  the  corresponding  eye. 

In  the  affection  known  as  hemiopia,  the  patient  sees  only  one  lateral 
half  of  objects  presented  to  his  view.  His  field  of  vision,  instead  of 
being  circular,  has  the  form  of  a  semicircle ;  being  divided  at  its  mid- 
dle by  a  vertical  diameter,  on  one  side  of  which  everything  is  invisible. 
Such  a  condition  may  be  produced  by  lesions  affecting  one  of  the  optic 
tracts  behind  the  chiasma,  as  at  B,  Fig.  122.  As  the  direct  fibres,  on 
the  outer  border  of  each  tract,  pass  to  the  external  portion  of  the  retina 
on  the  same  side,  and  the  cross  fibres  pass  to  the  internal  portion  of  the 
opposite  eye,  both  eyes  will  be  blinded  in  the  corresponding  half  of  the 
retina,  and  for  the  opposite  half  of  the  field  of  vision.  If  the  lesion 
involve  the  left  optic  tract,  as  in  Fig.  122,  the  right  lateral  half  of  the 


*  Archives  de  Physiologic.     Paris,  1878,  2me  serie,  tome  v.,  p.  658. 


454 


THE    NERVOUS    SYSTEM. 


FIG.  122. 


field  of  vision  will  be  obliterated ;  since  it  is  the  left  half  of  each  retina 
which  receives  rays  coming  from  the  right  side,  and  vice  versa. 

On  the  other  hand  a  lesion  situated  at  the  front  of  the  chiasma,  and 
on  the  median  line,  as  at  C,  Fig.  122,  will  interrupt  only  the  crossed 
fibres,  which  supply  the  inner  portion  of  both  eyes.  This  will  produce 
a  hemiopia  in  which  the  left  eye  is  blind  for  the  left  half  of  the  visual 
field,  and  the  right  eye  is  blind  for  its  right  half.  The  whole  field  of 
vision  is  therefore  perceptible  when  both  eyes  are  used ;  but  when 
either  of  them  is  covered,  the  defect  becomes  apparent. 

Exactly  the  opposite  condition  is  that  in  which  the  left  half  of  the 
field  of  vision  is  obliterated  for  the  right  eye,  and  the  right  half  for  the 

left  eye.  This  may  be  caused 
by  injuries  affecting  simultane- 
ously the  outer  border  of  the 
chiasma  on  both  sides,  as  at  D, 
D,  Fig.  122 ;  by  which  the  di- 
rect fibres  going  to  each  eye  are 
interrupted,  while  the  cross  fibres 
remain  intact.  According  to 
the  citations  of  Charcot,*  all 
these  forms  of  hemiopia  have 
been  observed  in  company  with 
the  corresponding  lesions. 

Lastly,  unilateral  blindness, 
that  is,  blindness  of  one  eye 
(amblyopia),  may  be  produced 
by  cerebral  lesions,  indepen- 
dently of  any  injury  to  the  optic 
nerves  or  tracts.  It  has  already 
been  seen  (page  430)  that  in 
the  dog  unilateral  blindness,  on 
the  opposite  side,  may  result 
from  destruction  of  a  portion 
of  the  cortical  layer  of  the  hemi- 
sphere. In  man,  as  shown  by 
Charcot,  f  hemianaesthesia,  from 
lesion  of  the  posterior  part  of 
the  internal  capsule  or  corona 
radiata,  is  accompanied,  as  a 
rule,  by  impairment  of  vision  in 
the  opposite  eye.  This  is  no  doubt  due  to  interruption  of  the  ncrvo 
fibres  between  the  central  terminations  of  the  optic  tract  (corpora 
geniculata,  optic  thalamus,  and  tubercula  quadrigemina)  and  the  cere- 


LESIONS  OF  THE  OPTIC  NERVES  AND  TRACTS.— A.  Le- 
sion of  Right  Optic  Nerve ;  blindness  of  Right  Eye. 
B.  Lesion  of  Left  Optic  Tract;  hemiopia  of  left 
side,  both  eyes.  C.  Lesion  of  Decussating  Fibres 
of  the  Chiasma;  internal  hemiopia,  both  eyes.  D, 
D.  Double  Lesion  of  Direct  Fibres ;  external  hemi- 
opia, both  eyes. 


*  Lepons  sur  lea  Localisations  dans  les  Maladies  du  Cerveau.     Paris,  1878,  pp 
124,  125,  126. 
f  Ibid.,  pp.  119,  120,  121,  129. 


THE    CRANIAL    NERVES.  455 

bral  convolutions.  It  is  often  unaccompanied  by  any  perceptible  altera- 
tion in  the  tissues  of  the  eyeball  or  the  optic  nerves. 

But  it  is  not  easy  to  account  for  blindness  confined  to  the  opposite 
eye,  from  lesions  on  one  side  of  the  brain,  if  each  optic  tract  contains 
fibres  destined  for  both  eyes.  We  know  that  injury  of  one  optic  tract 
produces  hemiopia  in  both  eyes ;  and  the  only  plausible  explanation  of 
this  fact  is  in  the  supposed  double  distribution  of  its  fibres.  But  it  is 
equally  certain  that  cerebral  lesions  of  one  side,  above  and  behind  the 
optic  tracts,  produce,  on  the  contrary,  blindness  in  the  opposite  eye. 
It  is  supposed  by  Charcot  that  a  supplementary  crossing  may  take  place 
behind  the  central  attachment  of  the  optic  tracts,  like  that  indicated 
in  Figs.  121  and  122.  According  to  this  view  the  crossed  fibres  of  the 
right  optic  tract,  which  have  come  from  the  left  eye,  communicate  with 
the  right  side  of  the  brain ;  while  its  direct  fibres,  which  have  come 
from  the  right  eye,  cross  the  median  line,  perhaps  in  the  tubercula 
quadrigemina,  and  communicate  with  the  left  side  of  the  brain.  Thus 
a  region  somewhere  in  the  cortex  of  the  left  hemisphere  will  represent 
all  the  fibres  coming  from  the  right  eye,  and  a  corresponding  region 
in  the  right  hemisphere  will  represent  all  those  from  the  left  eye.  This 
hypothesis  still  leaves  some  points  of  difficulty  in  regard  to  unilateral 
blindness  and  hemiopia,  but  it  affords  the  most  rational  explanation  of 
their  principal  phenomena. 

In  birds,  the  reflex  stimulus  which  causes  contraction  of  the  pupil 
passes,  owing  to  the  complete  decussation  of  their  nerves,  to  the  optic 
tubercle  of  the  opposite  side.  But  here,  by  the  transverse  connection 
of  the  parts,  it  becomes  duplicated ;  and  a  beam  of  light,  falling  upon 
one  retina,  will  produce  contraction  in  both  pupils.  Even  when  one 
optic  tubercle  has  been  removed  and  the  opposite  eye  permanently 
blinded,  both  pupils  will  contract  under  the  stimulus  of  light  falling 
upon  the  sound  eye.  In  examining  an  eye,  therefore,  either  in  animals 
or  in  man,  to  determine  whether  it  be  sensitive  to  light,  the  opposite 
eye  should  always  be  covered,  in  order  to  prevent  its  exciting  a  move- 
ment by  crossed  reflex  action. 

Third  Pair.    The  Oeulomotorius. 

The  oculomotorius  nerve,  so  called  because  it  supplies  most  of  the 
muscles  moving  the  eyeball,  originates  from  a  collection  of  gray  sub- 
stance next  the  median  line,  beneath  the  tubercula  quadrigemina  and 
the  aqueduct  of  Sylvius.  As  this  group  of  nerve  cells  is  continuous 
with  that  which  gives  origin  to  the  fourth  nerve  or  patheticus,  it  is 
designated  as  the  common  nucleus  of  the  oculomotorius  and  patheticus 
nerves.  From  this  nucleus  the  fibres  of  the  oculomotorius  pass  down- 
ward and  forward,  through  the  crus  cerebri,  until  they  emerge,  in  the 
form  of  several  flattened  bundles,  from  its  inner  border,  a  little  in  front 
of  the  pons  Yarolii.  They  then  unite  into  a  rounded  cord,  which  runs 
forward  and  outward,  to  penetrate  the  cavity  of  the  orbit  by  the 
sphenoidal  fissure.  During  this  transit  the  nerve  receives  one  or  two 


456  THE    NERVOUS    SYSTEM. 

twigs  of  sensitive  fibres  from  the  trigeminus.  On  entering  the  orbit, 
it  divides  into  several  branches,  supplying  the  superior,  inferior,  and 
internal  straight  muscles  of  the  eyeball,  the  inferior  oblique,  and  the 
levator  palpebrse  superioris.  The  oculomotorius  is  accordingly  con- 
cerned both  in  the  vertical  and  lateral  movements  of  the  eyeball,  and 
in  those  of  rotation ;  while  of  the  two  other  muscular  nerves  of  this 
organ,  the  abducens  is  connected  only  with  the  movement  of  abduc- 
tion, the  patheticus  only  with  that  of  rotation. 

Decussation  of  the  Oculomotorius  Nerve. — According  to  Meynert, 
a  decussation  takes  place  between  the  oculomotorius  nucleus  and  the 
opposite  side  of  the  brain  by  fibres  crossing  the  median  line  in  the 
raphe,  near  which  the  nucleus  is  situated.  These  fibres  come  originally 
from  the  corpus  striatum,  thence  run  backward  along  the  inner  border 
of  the  crus  cerebri,  and  into  the  longitudinal  lamina  forming  the  raphe. 
Underneath  the  aqueduct  of  Sylvius  they  decussate  at  an  acute  angle, 
those  from  the  right  corpus  striatum  passing  to  the  nucleus  of  the  left 
side,  and  vice  versa.  Each  oculomotorius  nerve  is  therefore  in  con- 
nection with  the  opposite  side  of  the  brain,  not  by  means  of  its  own 
fibres,  but  through  the  intervention  of  its  nucleus  and  the  fibres  which 
pass  thence,  through  the  raphe,  to  the  opposite  corpus  striatum. 

Physiological  Properties  of  the  Oculomotorius  Nerve. — The  oculo- 
motorius is  in  itself  an  exclusively  motor  nerve,  and  has  been  found  by 
Longet,  near  its  point  of  emergence  from  the  crus  cerebri,  insensible 
to  mechanical  irritation ;  but  at  some  distance  farther  forward,  after 
receiving  its  branches  of  communication  from  the  trigeminus,  it  exhibits 
a  certain  degree  of  sensibility.  Its  excitability,  on  the  contrary,  is 
very  manifest ;  and  its  irritation  within  the  cranial  cavity,  even  after 
its  separation  from  the  brain,  causes  convulsive  action  in  the  muscles 
of  the  eyeball. 

The  physiological  function  of  this  nerve  is  shown  by  the  paralysis 
following  its  section  either  before  or  after  its  entrance  into  the  orbit. 
These  results  are  for  the  most  part  simple  and  well  marked,  and  are 
established  by  the  uniform  testimony  of  various  observers.  They  con- 
sist of  the  paralysis  of  the  five  muscles  to  which  the  nerve  is  distributed, 
and  induce,  consequently ; 

1.  External   strabismus,   from   continued   action   of    the   external 
straight  muscle  of  the  eyeball,  which  is  no  longer  antagonized  by  the 
internal. 

2.  Immobility  of  the  eyeball,  owing  to  the  abolition  of  its  upward, 
downward,  lateral,  and  rotatory  movements.      For  although  two  of 
the  muscles  of  the  eyeball,  namely,  the  external  rectus  and  the  superior 
oblique,  remain  unparalyzed ;  yet,  as  they  are  no  longer  antagonized 
by  the  remainder,  they  can  only  produce  a  permanent  deviation  of  the 
eyeball,  but  no  alternate  movement  in  different  directions.     In  most  of 
the  lower  animals  there  is  also  an  unusual  prominence  of  the  eyeball, 
owing  to  paralysis  of  the  retractor  muscles. 

3.  Drooping  of  the  upper  eyelid.     In  the  ordinary  action  of  opening 


THE    CRANIAL    NERVES.  457 

the  eye,  it  is  the  upper  eyelid  alone  which  moves,  being  raised  to 
uncover  the  cornea  and  pupil,  by  the  levator  palpebrse  superioris.  As 
this  muscle  is  animated  by  a  branch  of  the  oculomotorius,  it  is  paralyzed 
by  section  of  this  nerve  at  the  same  time  with  the  muscles  moving  the 
eyeball.  The  consequence  is  that  the  eye  can  no  longer  be  fully  opened ; 
though  it  can  be  closed  as  usual  by  the  action  of  the  orbicularis  oculi, 
which  is  supplied  from  the  seventh  pair.  The  eyelid  therefore  droops, 
resting  in  such  a  position  as  to  cover  the  upper  portion  of  the  cornea, 
and  the  greater  part  or  even  the  whole  of  the  pupil.  This  condition  is 
known  as  ptosis,  and  is  one  of  the  consequences  following  paralysis  of 
the  oculomotorius  nerve. 

The  influence  of  the  oculomotorius  on  the  contractile  movements  of 
the  iris  is  important,  though  less  distinct  and  uniform  than  that 
exerted  on  the  movements  of  the  eyeball.  The  connection  of  the 
oculomotorius  with  the  muscular  apparatus  of  the  iris  is  indirect,  tak- 
ing place  through  the  intervention  of  the  ophthalmic  ganglion,  to  which 
it  sends  a  motor  branch,  and  which  in  turn  gives  off  the  ciliary  nerves 
for  the  iris.  Some  observers  (Mayo,  Longet)  have  found  well-marked 
paralysis  of  the  iris  following  division  of  the  oculomotorius  nerve,  and 
enumerate,  as  consequences  of  this  injury,  permanent  dilatation  and 
immobility  of  the  pupil.  In  the  experiments  of  Longet,  on  dogs,  rab- 
bits, and  pigeons,  irritation  of  the  cephalic  extremity  of  the  optic  nerve 
caused  contraction  of  the  pupil  in  both  eyes ;  but  after  division  of  the 
oculomotorius  nerve  the  effect  was  no  longer  produced  on  the  operated 
side.  Bernard  has  also  found  that  division  of  the  oculomotorius  is  fol- 
lowed, in  the  rabbit,  by  dilatation  of  the  pupil,  and  that  in  the  operated 
eye  the  iris  contracts  only  very  slowly  and  imperfectly  under  the  influ- 
ence of  light.  It  is  not,  however,  completely  paralyzed,  since  it  may 
still  move  with  considerable  promptitude  under  the  influence  of  painful 
impressions  conveyed  by  the  fifth  pair.  The  action  of  the  oculomo- 
torius on  the  pupil,  therefore,  is  energetic  and  constant  in  the  ordinary 
reflex  movement  of  contraction  under  the  stimulus  of  light;  but  it 
takes  place  through  the  ophthalmic  ganglion,  to  which  it  communi- 
cates, in  a  certain  degree,  its  motive  power. 

Fourth  Pair.    The  Patheticns. 

This  nerve  presents  certain  peculiarities,  which,  notwithstanding  its 
minute  size,  have  attracted  to  it  special  attention.  It  is  distributed 
exclusively  to  the  superior  oblique  muscle  of  the  eyeball ;  its  name  hav- 
ing been  derived  from  the  erroneous  idea  that  this  muscle  turned  the 
eye  upward  and  inward.  Both  the  superior  and  inferior  oblique  mus- 
cles, however,  have  been  fully  shown  to  cause  in  the  eyeball  a  nearly 
simple  movement  of  rotation  about  its  longitudinal  axis.  They  are 
antagonistic  to  each  other ;  and  by  their  contraction  and  relaxation, 
during  movements  of  inclination  of  the  head  from  side  to  side,  they 
maintain  the  horizontal  planes  of  the  eyeballs  in  the  same  position. 
If  this  parallelism  were  not  preserved,  objects  would  appear  to  stand  in 


458  THE    NERVOUS    SYSTEM. 

different  degree?  of  obliquity  to  the  two  eyes,  producing  uncertainty 
and  double  vision. 

The  apparent  origin  of  the  patheticus  nerve  is  immediately  behind 
the  tubercula  quadrigemina,  on  the  upper  surface  of  the  valve  of 
Vieussens,  a  thin  lamina  of  white  substance,  covering  the  anterior  part 
of  the  fourth  ventricle.  The  root  fibres  of  the  nerve,  however,  can  be 
traced  transversely  through  the  substance  of  the  valve.  According  to 
Henlc  and  Meyuert,  a  great  part  cross  the  median  line,  decussating 
with  those  from  the  corresponding  nerve  on  the  opposite  side ;  then, 
turning  downward  and  forward,  they  reach  a  collection  of  gray  matter 
just  behind  the  nucleus  of  the  oculomotorius  nerve,  and  continuous 
with  it.  According  to  Henle,  a  portion  of  the  fibres  also  terminate, 
without  crossing  the  median  line,  in  the  nucleus  of  the  same  side.  The 
nucleus  is  situated  beneath  the  aqueduct  of  Sylvius  and  the  anterior 
tubercula  quadrigemina ;  while  the  point  of  exit  of  the  nerve  is  above 
the  aqueduct  of  Sylvius  and  behind  the  posterior  tubercula  quadri- 
gemina. Its  root  fibres,  accordingly,  after  leaving  their  nucleus  of 
origin,  encircle  the  walls  of  the  aqueduct,  running  obliquely  upward 
and  backward,  and  then  crossing  the  median  line  to  their  emergence 
on  the  opposite  side. 

From  this  point,  the  nerve  passes  forward,  as  a  slender  filament,  not 
more  than  one  millimetre  in  diameter,  along  the  upper  wall  of  the 
cavernous  sinus,  where  it  lies  in  immediate  proximity  to  the  oculo- 
motorius ;  and  thence,  entering  the  cavity  of  the  orbit  by  the  sphenoidal 
fissure,  terminates  in  the  superior  oblique  muscle  of  the  eyeball. 

The  course  of  the  oculomotorius  and  patheticus,  when  compared, 
shows  a  remarkable  relation  between  the  two  nerves.  Their  fibres 
originate  from  adjacent  portions  of  the  same  nucleus.  Those  of 
the  oculomotorius  pass  downward  and  forward,  to  emerge  from  the 
inner  border  of  the  crus  cerebri,  at  the  base  of  the  brain ;  while  those 
of  the  patheticus  pass  upward  and  backward,  emerging  from  the  valve 
of  Vieussens,  between  the  cerebrum  and  cerebellum.  But  the  nerves 
afterward  run  side  by  side,  in  their  passage  toward  the  orbit,  and  are 
finally  distributed  to  muscles  associated  in  the  movements  of  the  same 
organ. 

Physiological  Properties  of  the  Patheticus  Nerve. — The  distribution 
of  this  nerve  to  a  muscle  which  receives  filaments  from  no  other  source 
indicates  in  great  measure  its  motor  character,  which  is  furthermore 
established  by  the  results  of  observation.  The  experiments  of  Chnu- 
veau  on  the  horse  and  rabbit,  and  those  of  Longet  on  the  horse,  ox, 
and  dog,  show  that  galvanization  of  this  nerve  within  the  cranium 
produces  contraction  of  the  superior  oblique  muscle,  with  rotation  of 
the  eyeball  on  its  longitudinal  axis  from  without  inward;  and  in  those 
of  Longet  there  was  also  a  deviation  of  the  pupil  outward.  In  < 
quoted  by  Longet,  attributed  to  paralysis  of  this  nerve,  in  man,  there 
was  incapacity  of  rotation  of  the  eyeball  on  the  aiVected  side,  and  con- 
sequently double  vision,  the  image  perceived  by  the  affected  eye  being 


THE    CRANIAL    NERVES.  459 

oblique  and  inferior  in  regard  to  the  other ;  but  these  disturbances  of 
vision  disappeared  when  the  head  was  inclined  toward  the  opposite  side. 
The  patheticus  is,  accordingly,  the  motor  nerve  of  the  superior 
oblique  muscle,  and  acts  in  harmony  with  the  oculomotorius  to 
preserve  the  horizontal  plane  of  the  eyeball. 

Fifth  Pair.    The  Trigeminus. 

The  fifth  pair  occupies,  in  every  respect,  a  prominent  place  among 
the  cranial  nerves.  It  is  the  great  sensitive  nerve  of  the  face,  being 
the  only  source  of  general'  sensibility  for  the  integument  and  mucous 
membranes  of  this  region ;  and,  by  branches  of  communication  to  the 
corresponding  motor  nerves,  it  provides  for  the  imperfect  sensibility 
of  the  facial  muscles.  But  while  in  its  main  portion  it  is  preeminently 
sensitive,  it  also  possesses  motor  fibres,  derived  from  a  distinct  root,  and 
distributed  to  muscles  of  a  special  group.  Before  emerging  from  the 
cranial  cavity  it  separates  into  three  main  divisions,  destined  for  the 
corresponding  regions  of  the  face ;  and  its  name,  trigeminus,  is  derived 
from  the  fact  that  in  man  these  three  primary  divisions  are  nearly 
alike  in  size  and  importance. 

The  apparent  origin  of  the  fifth  nerve  is  from  the  lateral  portion  of 
the  pons  Yarolii,  where  its  two  roots  emerge  in  close  approximation 
to  each  other,  but  usually  separated  by  a  narrow  band  of  the  trans- 
verse fibres  of  the  pons.  The  anterior  or  motor  root  is  the  smaller 
of  the  two,  being  about  two  millimetres  in  diameter ;  the  posterior  or 
sensitive  root  is  the  larger,  having  a  diameter  of  about  five  millimetres. 
Both  roots  may  be  traced,  through  the  pons  Yarolii,  backward,  upward, 
and  inward,  to  the  gray  substance  beneath  the  anterior  part  of  the 
fourth  ventricle.  During  the  greater  part  of  this  passage  they  remain 
distinct,  but  join  each  other  above  and  become  closely  entangled  by  the 
interweaving  of  their  bundles ;  though  their  fibres  may  still  be  distin- 
guished, on  microscopic  examination,  by  the  generally  larger  size  of 
those  belonging  to  the  motor  root.  They  finally  reach  a  collection  of 
gray  substance,  the  "trigeminal  nucleus,"  situated  next  behind  that 
of  the  oculomotorius  and  patheticus,  but  farther  outward  from  the 
median  line,  occupying  the  extreme  lateral  part  of  the  fourth  ven- 
tricle, where  its  floor  forms  an  angle  with  the  roof.  The  fibres  of  the 
nerve  terminate  partly  in  or  among  the  large,  stellate,  and  dark-colored 
cells  of  this  nucleus.  According  to  Henle,  a  portion  also  pass  through 
the  nucleus,  and  across  the  median  line  to  the  opposite  side ;  the  two 
sets  together  forming,  in  this  way,  partly  a  direct  and  partly  a  crossed 
connection  between  the  peripheral  organs  and  the  nervous  centres. 

After  emerging  from  the  pons  Yarolii,  the  two  roots  of  the  fifth  nerve 
pass  outward  and  forward  in  company  with  each  other,  the  larger,  pos- 
terior, or  sensitive  root  being  placed  above,  the  smaller,  anterior,  or 
motor  root  underneath.  At  the  apex  of  the  petrous  portion  of  the 
temporal  bone,  a  little  outside  and  behind  the  posterior  clinoid  process 
of  the  sella  turcica,  the  fibres  of  the  sensitive  root  spread  out  into  a 


460 


TITi:    NERVOUS    SYSTEM 


network  of  inosculating  bundles,  in  the  substance  of  the  Gasserian 
ganglion.  This  ganglion  forms  a  flattened,  crescentic  mass  of  gray  sub- 
stance, mingled  with  the  fibres  from  the  sensitive  root.  The  ganglionic 
cells  are  unipolar  in  form,  giving  off  fibres  in  a  peripheral  direction, 
which,  according  to  Key  and  Retzius,  unite  with  those  of  cerebral  origin 

FIG.  123. 


DIAGRAM  OF  THE  FIFTH  NKRVE  AND  ITS  DISTRIBUTION.— 1.  Sensitive  root.  2.  Motor  root.  3.  Gas- 
serian ganglion.  I.  Ophthalmic  division.  II.  Superior  maxillary  division.  III.  Inferior  maxillary 
division.  4.  Supra-orbital  nerve,  distributed  to  the  skin  of  the  forehead,  inner  angle  of  the  eye, 
and  root  of  the  nose.  6.  Infra-orbital  nerve;  to  the  skin  of  the  lower  eyelid,  side  of  the  nose, 
and  skin  and  mucous  membrane  of  the  upper  lip.  6.  Mental  nerve ;  to  the  integument  of  the 
chin  and  edge  of  the  lower  jaw,  and  skin  and  mucous  membrane  of  the  lower  lip.  n,  n.  External 
terminations  of  the  nasal  branch  of  the  ophthalmic  division;  to  the  mucous  membrane  of  the 
inner  part  of  the  eye  and  the  nasal  passages,  and  to  the  base,  tip,  and  wing  of  the  nose.  t.  Tem- 
poral branch  of  the  superior  maxillary  division;  to  the  skin  of  the  temporal  region,  m.  Malar 
branch  of  the  superior  maxillary  division ;  to  the  skin  of  the  cheek  and  neighboring  parts,  b.  Buccal 
branch  of  the  inferior  maxillary  division;  passing  along  the  surface  of  the.  buccinator  muscle, 
and  distributed  to  the  mucous  membrane  of  the  cheek,  and  to  the  mucous  membrane  ami  skin 
of  the  lips.  f.  Lingual  nerve;  to  the  mucous  membrane  of  the  anterior  two-thirds  of  the  tongue. 
at.  Auriculo  temporal  branch  of  the  inferior  maxillary  division  ;  to  the  skin  of  the  anterior  part 
of  the  external  ear  and  adjacent  temporal  region,  x,  x, x.  Muscular  branches;  to  the  temporal, 
masseter,  and  internal  ami  external  pterygoid  muscles,  y.  Muscular  branch;  to  the  mylo-byoid 
and  anterior  belly  of  the  diagastric.  /.  Sensitive  branch  of  communication  to  the  facial  ner\ -e. 


in  the  sensitive  root.  The  motor  root  passes  beneath  the  ganglion 
as  a  distinct  bundle,  neither  giving  nor  receiving  any  communicating 
fibres.  At  the  anterior  border  of  the  ganglion,  the  nerve  separates 
into  its  three  bundles,  namely,  the  first,  or  ophthalmic;  the  second, 


THE    CRANIAL    NERVES.  461 

or  superior  maxillary ;  and  the  third,  or  inferior  maxillary  divisions 
of  the  trigeminus. 

The  ophthalmic  division  passes  through  the  sphenoidal  fissure  into 
the  orbit  of  the  eye,  where  it  gives  filaments  to  the  ophthalmic  ganglion 
and  to  the  eyeball ;  a  nasal  branch,  supplying  the  integument  and 
mucous  membrane  of  the  inner  part  of  the  eye,  the  mucous  membrane 
of  the  middle  and  inferior  nasal  passages,  and  the  integument  of  the 
root,  wing,  and  tip  of  the  nose ;  and  a  branch  to  the  lachrymal  gland 
and  the  integument  of  the  upper  eyelid  and  adjacent  region.  It  then 
emerges  from  the  orbit  by  the  supra-orbital  notch,  and  is  distributed 
to  the  skin  of  the  forehead  and  side  of  the  head,  as  far  back  as  the 
vertex. 

The  superior  maxillary  division  passes  through  the  foramen  rotun- 
dum  into  the.  spheno-maxillary  fossa,  where  it  gives  a  sensitive  branch 
to  the  spheno-palatine  ganglion  of  the  sympathetic,  thence  through  the 
longitudinal  canal  in  the  floor  of  the  orbit,  where  it  gives  off  a  branch 
running  upward  and  outward  to  the  skin  of  the  malar  and  temporal 
regions,  and  numerous  descending  branches  to  the  teeth,  gums,  and 
adjacent  mucous  membrane  of  the  upper  jaw,  and  to  that  of  the  inferior 
nasal  passages.  It  then  emerges  upon  the  face  by  the  infra-orbital 
foramen,  and  is  distributed  to  the  integument  of  the  lower  eyelid  and 
the  side  of  the  nose,  and  to  the  skin  and  mucous  membrane  of  the 
upper  lip. 

The  inferior  maxillary  division  leaves  the  anterior  border  of  the 
Gasserian  ganglion  at  a  different  angle  from  the  two  others,  passing 
almost  vertically  downward  through  the  foramen  ovale.  This  division 
receives  all  the  fibres  of  the  motor  root,  which  become  more  intimately 
united  with  it  during  its  passage  through  the  base  of  the  skull.  While 
the  two  other  divisions  of  the  fifth  nerve  are  therefore  exclusively  sen- 
sitive, the  inferior  maxillary  division  is  a  mixed  nerve,  containing  both 
motor  and  sensitive  fibres. 

After  supplying  one  or  two  filaments  to  the  otic  ganglion  of  the 
sympathetic,  and  while  passing  down  toward  the  inferior  dental  canal, 
it  gives  off  two  sensitive  branches,  namely,  1st,  the  buccal  (Fig.  123,  b) 
to  the  mucous  membrane  of  the  cheek,  and  the  skin  and  mucous  mem- 
brane of  the  lips ;  and  2d,  the  auriculo-temporal  branch  (at),  which 
turns  backward  and  upward,  to  be  distributed  to  the  integument  of 
the  anterior  wall  of  the  external  auditory  meatus,  the  anterior  part 
of  the  external  ear,  and  the  adjacent  temporal  region.  From  this 
branch  a  twig  of  considerable  size  (/)  turns  forward  to  join  the  facial 
nerve,  communicating  to  its  branches  in  front  of  this  point  a  percep- 
tible degree  of  sensibility. 

Another  sensitive  branch  of  this  portion  of  the  nerve  is  the  lingual 
(I),  which  sends  filaments  to  the  submaxillary  gland,  the  sympathetic 
submaxillary  ganglion,  and  adjacent  mucous  membrane  of  the  mouth, 
and  is  mainly  distributed  to  the  mucous  membrane  and  papillae  of  the 
tip,  edges,  and  surface  of  the  anterior  two-thirds  of  the  tongue.  The 


462  THE    NERVOUS    SYSTEM. 

motor  branches  are  those  (x,  x,  x)  going  to  the  temporal,  masseter, 
and  two  pterygoid  muscles,  and  that  distributed  (y)  to  the  mylohyoid 
muscle  and  the  anterior  belly  of  the  digastric. 

The  remaining  portion  of  the  trigeminus  then  enters  the  dental  canal 
of  the  inferior  maxilla,  through  which  it  passes,  giving  off  filaments  to 
the  teeth  and  gums  of  the  lower  jaw.  It  finally  emerges  at  the  mental 
foramen,  and  is  distributed  in  numerous  diverging  ramifications  to  the 
integument  of  the  chin  and  edge  of  the  under  jaw,  and  the  skin  and 
mucous  membrane  of  the  lower  lip. 

Physiological  Properties  of  the  Fifth  Pair. — The  most  prominent 
character  of  this  nerve  is  its  general  sensibility.  The  regions  to  which 
it  is  distributed,  namely,  the  cheeks,  eyelids,  tip  of  the  nose,  lips,  an- 
terior nares,  and  especially  the  tip  of  'the  tongue,  possess  a  tactile  sen- 
sibility of  higher  grade  than  most  other  parts  of  the  body.  The  nerve 
itself,  together  with  its  principal  branches,  is  acutely  sensitive  to  me- 
chanical irritation,  and  will  give  rise  to  indications  of  sensibility  under 
conditions  when  the  spinal  nerves  are  nearly  or  quite  inactive. 

But  the  most  direct  and  conclusive  proof  of  the  function  of  this 
nerve  is  the  loss  of  sensibility  produced  by  its  division.  If  either 
the  infraorbital  or  the  mental  branch  be  divided  at  its  exit  from  the 
superior  or  inferior  maxilla,  tactile  sensibility  is  impaired  or  abolished 
in  the  corresponding  region  of  the  face.  A  still  more  striking  result 
is  produced  by  dividing  the  entire  nerve  within  the  cranium.  This 
operation,  which  was  first  performed  by  Magendie,  may  be  done,  upon 
the  cat  or  the  rabbit,  by  means  of  a  steel  instrument  with  a  slender 
shank  and  a  narrow  cutting  blade  projecting  at  nearly  a  right  angle 
from  its  extremity.  The  instrument  is  introduced  in  a  horizontal  direc- 
tion through  the  squanious  portion  of  the  temporal  bone,  and  pushed 
inward  and  forward,  with  its  blade  lying  flatwise  on  the  floor  of  the 
skull,  until  it  strikes  the  posterior  clinoid  process.  It  is  then  slightly 
withdrawn,  its  cutting  edge  turned  downward,  and  the  nerve  divided 
where  it  crosses  the  petrous  portion  of  the  temporal  bone.  By  this 
method  all  its  fibres  are  cut  off,  and  the  only  part  of  the  brain  neces- 
sarily wounded  is  the  inferior  portion  of  the  temporal  lobe. 

The  immediate  effect  of  this  operation  is  a  complete  anaesthesia  of 
the  integument  and  mucous  membranes  about  the  face  on  the  operated 
side.  The  cornea  can  be  touched  without  exciting  any  movement  of 
the  eyelids.  A  probe  may  be  introduced  into  the  nasal  passages,  or  the 
lips  may  be  pierced  with  a  needle,  without  eliciting  any  sign  of  sensa- 
tion on  the  part  of  the  animal.  At  the  same  time  the  power  of  motion 
in  these  parts  is  unaffected.  The  eyelids  may  be  opened  or  closed  under 
the  influence  of  visual  impressions,  and  the  movements  of  the  lips  con- 
tinue to  be  performed  in  a  nearly  natural  manner.  In  the  cat,  the  loss 
of  sensibility  and  persistence  of  the  power  of  motion  is  shown  by  irri- 
tating at  different  points  the  integument  of  the  external  ear,  which  in 
this  animal  has  an  acute  tactile  sensibility.  If  a  pointed  instrument 
be  brought  in  contact,  on  the  operated  side,  with  the  anterior  part  of 


THE    CRANIAL    NERVES.  463 

the  ear,  which  is  supplied  by  fibres  from  the  third  division  of  the  fifth 
nerve,  no  effect  is  produced.  But  if  the  same  irritation  be  applied  to 
the  back  part  of  the  ear,  which  is  supplied  by  the  great  auricular 
nerve  from  the  cervical  plexus,  a  twitching  movement  is  at  once 
excited.  According  to  Longet,  the  most  violent  injuries,  such  as 
exsection  of  the  eyeball,  evulsion  of  the  hairs  about  the  lips,  extraction 
of  the  teeth,  or  destruction  of  the  integument  by  the  actual  cautery, 
may  be  performed,  after  complete  division  of  the  fifth  nerve,  without 
causing  any  painful  sensation. 

The  fifth  pair  is  accordingly  the  exclusive  source  of  sensibility  in 
the  superficial  regions  of  the  face,  and  all  parts  of  the  nasal  and  buccal 
cavities  to  which  it  is  distributed. 

Painful  Affections  of  the  Fifth  Pair. — This  nerve  is  also  the  seat 
of  neuralgic  affections  about  the  head  and  face.  The  most  common  of 
these  is  headache ;  which  may  be  general,  extending  over  the  whole 
forehead  and  vertex,  or  confined  to  one  side.  It  often  seems  to  be 
located  in  the  branches  supplying  the  periosteum,  especially  of  that 
lining  the  orbit  and  the  frontal  sinuses.  Where  the  pain  is  deep-seated, 
its  location  may  be  in  the  dura  mater  or  the  bones  of  the  skull ;  since 
each  division  of  the  fifth  pair,  either  before  or  immediately  after  leaving 
the  cavity  of  the  cranium,  sends  a  slender  recurrent  branch  to  the  dura 
mater  and  the  cranial  bones.  That  from  the  ophthalmic  division  may 
be  traced  into  the  tentorium,  in  which  it  ramifies  as  far  as  the  sinuses 
bordering  its  attached  edge. 

Toothache,  from  irritation  of  the  dental  filaments  of  the  fifth  pair,  is 
generally  due  to  decay  of  the  dentine,  and  consequent  exposure  of  the 
tooth  pulp  to  mechanical  injury.  Neuralgia  of  the  teeth  may  also  be 
caused,  like  headache,  by  indigestion,  exposure,  or  fatigue ;  the  pain 
existing  simultaneously  in  several  teeth,  without  morbid  alteration  of 
their  structure. 

The  most  severe  and  persistent  form  of  neuralgia  in  this  nerve  is 
tic  douloureux;  habitually  located  in  one  of  its  three  principal  divisions 
as  they  emerge  upon  the  face.  The  pain  is  usually  intermittent,  recur- 
ring in  great  severity  at  various  intervals,  and  lasting  but  a  few  min- 
utes at  a  time.  It  is  most  frequently  seated  in  the  upper  and  middle 
regions  of  the  face,  corresponding  with  the  distribution  of  the  supra 
and  infraorbital  nerves. 

Lingual  Branch  of  the  Fifth  Pair. — This  branch,  known  as  the 
"  lingual  nerve,"  communicates  to  the  mucous  membrane  of  the 
tongue  its  tactile  sensibility.  This  sensibility  is  highly  developed  in 
the  anterior  two-thirds  of  the  tongue,  and  at  its  tip  is  more  acute  than 
in  any  other  region  of  the  body.  It  disappears  completely  on  the  oper- 
ated side,  when  the  fifth  nerve  has  been  divided  within  the  cranium ; 
and  after  section  of  both  lingual  nerves,  according  to  Longet,  it  is  lost 
in  the  whole  anterior  two-thirds  of  the  organ.  The  tactile  sensibility 
of  the  tongue  is  of  great  importance  in  man  and  many  animals,  as  an 
aid  in  mastication,  for  appreciating  the  physical  qualities  of  the  food, 


464  THE    NERVOUS    SYSTEM. 

to  perceive  when  it  is  reduced  to  the  proper  consistency  for  swallowing, 
and  to  detect  any  remnants  left  among  folds  or  crevices  of  the  mucous 
membrane. 

The  lingual  nerve  is  also  endowed  with  the  special  sensibility  of 
taste.  This  function  is  difficult  to  investigate  in  animals,  owing  to  the 
uncertainty  of  its  indications,  and  the  difficulty  of  isolating  separate 
regions  of  the  cavity  of  the  mouth.  Experiments  upon  man,  which  are 
made  with  comparative  facility,  have  been  performed  by  Guyot,  Ver- 
niere,  Duge"s,  and  Longet  in  such  a  manner  as  to  leave  no  doubt  that 
the  sense  of  taste  is  highly  developed  in  those  portions  of  the  tongue 
exclusively  supplied  by  the  lingual  nerve.  They  consist  mainly  in 
applying  to  different  parts  of  the  mucous  membrane  a  pellet  of  lint, 
moistened  with  a  solution  of  some  substance,  like  quinine  or  colocynth, 
possessing  a  distinct  taste  without  irritating  qualities.  In  this  way  it  is 
ascertained  that  the  point,  edges,  and  upper  surface  of  the  tongue,  through- 
out its  anterior  two-thirds,  is  capable  of  perceiving  sensations  of  taste, 
without  aid  from  other  parts  of  the  mucous  membrane.  According 
to  the  experiments  of  Bernard  and  Longet  on  animals,  division  of  the 
lingual  nerve  destroys  the  faculty  of  taste  as  well  as  that  of  general 
sensibility  in  the  corresponding  parts  of  the  tongue  ;  and  similar  obser- 
vations are  quoted  by  Henle,  after  section  of  this  nerve  in  man. 

Muscular  Branches  of  the  Fifth  Pair. — These  branches,  which  are 
all  given  off  from  the  inferior  maxillary  division  of  the  nerve,  are  dis- 
tributed to  the  temporal,  the  masseter,  and  the  external  and  internal 
pterygoid  muscles,  as  well  as  the  mylohyoid  muscle  and  the  anterior 
belly  of  the  digastric.  They  are  all  therefore  concerned  in  the  move- 
ments of  mastication.  The  most  powerful  of  the  muscles  to  which  they 
are  distributed,  namely,  the  temporal  and  the  masseter,  act  by  brin.tr- 
ing  the  teeth  of  the  lower  jaw  forcibly  in  contact  with  those  of  the 
upper.  The  action  of  the  pterygoid  muscles  produces  a  lateral  grind- 
ing movement,  by  which  the  trituration  of  the  food  is  accomplished ; 
and  finally  those  supplied  by  the  mylohyoid  branch  act  by  opening  the 
jaws,  to  allow  a  repetition  of  the  former  motions.  In  different  animals 
these  movements  vary  in  relative  importance.  In  the  carnivora,  the 
closure  of  the  jaws  preponderates  over  the  rest,  enabling  the  animal 
to  seize  and  retain  his  prey.  In  the  herbivora,  the  lateral  grinding 
movements  are  more  important  for  comminuting  the  seeds,  grains,  \ •( 'Ac- 
table fibres  and  other  hard  substances  upon  which  they  feed.  In  man, 
both  movements  exist  in  a  nearly  equal  degree. 

Anastomotic  Branches  of  the  Fifth  Pair. — Although  the  superior, 
middle,  and  inferior  regions  of  the  face  are  respectively  supplied,  in 
,u%eneral,  by  the  three  great  divisions  of  this  nerve,  there  is  yet  more 
or  less  communication  between  adjacent  branches,  so  that  each  region 
receives  fibres  from  different  sources.  Thus  the  infraorlutal  nerve, 
which  semis  filaments  to  the  lower  eyelid,  inosculates  with  a  branch 
of  the  ophthalmic  division.  The  integument  of  the  nose  is  supplied 
by  the  nasal  branches  of  the  ophthalmic  division,  and  also  by  those 


THE    CRANIAL    NERVES.  465 

coming  from  the  infraorbital  nerve.  The  upper  and  lower  lips  are  both 
supplied  from  the  infraorbital  and  mental  nerves  on  the  outside,  and 
from  the  terminal  filaments  of  the  buccal  nerve  on  the  inside ;  and  the 
temporal  region  receives  branches  both  from  the  superior  and  inferior 
maxillary  divisions.  A  most  important  anastomotic  branch  is  that  to 
the  facial  nerve  (Fig.  123,  /),  which  it  supplies  with  sensitive  filaments. 
Many  of  these  filaments  no  doubt  terminate  in  the  facial  muscles,  to 
which  they  communicate  a  certain  amount  of  sensibility ;  but  there  are 
also  abundant  anastomoses  between  the  facial  nerve  and  the  fifth  near 
their  final  distributions,  and  certain  regions  of  the  integument  may  be 
supplied  with  sensibility  from  this  source.  The  observations  of  L'Etie- 
vant  *  show  that  it  is  impossible,  in  man,  to  abolish  completely  the  sen- 
sibility of  any  extended  region  of  the  face  by  section  of  a  single  division 
of  the  fifth  pair ;  some  degree  of  sensibility  still  remaining,  due  to  in- 
osculatory  filaments  from  other  divisions  of  the  nerve,  either  directly 
or  through  the  branches  of  the  facial. 

According  to  Henle,  there  is  still  a  portion  of  the  side  of  the  face 
which  may  derive  sensibility  from  the  great  auricular  nerve  of  the 
cervical  plexus ;  since  the  anterior  branch  of  this  nerve,  after  supply- 
ing the  under  part  of  the  lobe  of  the  ear,  sends  some  slender  filaments 
forward  to  the  integument  of  the  cheeks,  in  some  instances  as  far  as 
the  neighborhood  of  the  malar  bone. 

Influence  of  the  Fifth  Pair  on  the  Special  Senses. — This  nerve  has 
an  important  connection  with  the  special  senses,  since  they  are  more 
or  less  impaired,  and  in  some  instances  practically  destroyed,  by  its 
division  or  injury.  Its  influence,  however,  is  mainly  indirect ;  showing 
itself  for  the  most  part  by  disturbance  of  nutrition  in  the  tissues  of  the 
organ  after  the  nerve  has  been  cut  off.  These  effects  seem  to  depend, 
not  on  the  division  of  the  ordinary  sensitive  fibres  of  the  nerve,  but  on 
that  of  sympathetic  fibres  derived  from  the  Gasserian  ganglion,  or  sup- 
plied, through  its  branches,  to  the  organs  of  sense. 

Influence  on  the  Sense  of  Smell. — The  nasal  passages  are  supplied 
by  two  different  cerebro-spinal  nerves,  namely,  the  olfactory  nerve, 
distributed  to  their  upper  portions,  and  endowed  with  special  sensi- 
bility ;  and  the  nasal  branches  of  the  fifth  pair,  distributed  in  the  lower 
portions,  to  which  they  communicate  general  sensibility.  The  mucous 
membrane  also  contains  filaments  from  the  spheno-palatine  ganglion 
of  the  sympathetic ;  which,  in  turn,  receives  its  sensitive  root  from  the 
superior  maxillary  division  of  the  fifth  pair. 

The  general  sensibility  of  the  nasal  passages  may  accordingly  remain 
after  the  sense  of  smell  has  been  destroyed.  But  if  the  fifth  pair  be 
divided,  not  only  is  general  sensibility  abolished  in  the  nasal  mucous 
membrane,  but  there  is  also  a  disturbance  in  its  nutrition,  which 
destroys  the  power  of  smell.  The  membrane  becomes  swollen,  and 
the  passages  are  obstructed  by  accumulation  of  mucus.  According  to 

*  Traite  des  Sections  Nerveuses.     Paris,  1873,  p.  179. 
2E 


466  THF     NERVOUS     SYSTKNf. 

Lon^et,  the  membrane  also  assumes  a  fungous  consistency,  and  is  liable 
to  bleed  at  the  slightest  touch.  It  is  owing  to  a  similar  condition  that 
the  power  of  smell  is  impaired  in  nasal  catarrh  or  influenza.  The  olfac- 
tory nerves  become  inactive  in  consequence  of  the  morbid  alteration  in 
their  mucous  membrane  and  its  secretions. 

tluence  on  the  Sense  of  Sight.— The  anterior  parts  of  the  eyeball 
art-  provided  with  nerves  of  ordinary  sensibility  from  the  fifth  pair; 
while  impressions  of  light  are  transmitted  exclusively  by  the  optic 
nerve.  The  iris  and  cornea  are  furthermore  supplied  by  filaments 
from  the  ophthalmic  ganglion  of  the  sympathetic,  which  receives  its 
sensitive  root  from  the  fifth  pair.  If  this  nerve  be  divided  either  in 
front  of  or  through  the  Gasserian  ganglion,  the  cornea  often  becomes 
the  seat  of  congestion  and  ulceration,  sometimes  resulting  in  complete 
destruction  of  the  eye.  Immediately  after  the  operation  the  pupil  is 
contracted  and  the  conjunctiva  loses  its  sensibility.  At  the  end  of 
twenty-four  hours  the  cornea  is  opaline,  and  by  the  second  day  the 
conjunctiva  is  congested,  and  discharges  a  purulent  secretion.  As 
the  process  increases  in  intensity,  the  cornea  grows  more  opaque, 
until  it  becomes  quite  impermeable  to  light,  and  vision  is  consequently 
suspended.  In  some  cases  there  is  at  last  sloughing  and  perforation 
of  the  cornea  and  discharge  of  the  humors  of  the  eye ;  in  others,  after 
a  few  days,  the  inflammatory  appearances  subside,  and  the  eye  is 
gradually  restored  to  its  natural  condition. 

According  to  Bernard,  these  effects  are  either  retarded  or  wanting 
when  the  nerve  is  divided  behind  the  Gasserian  ganglion.  This  indi- 
cates that  its  influence  on  the  nutrition  of  the  eyeball  does  not  reside 
in  the  fibres  of  its  own  roots,  but  in  additional  filaments  derived  from 
the  ganglion. 

Influence  on  the  Sense  of  Taste. — The  lingual  branch  of  the  fifth 
pair  communicates  to  the  anterior  portion  of  the  tongue  both  its  general 
sensibility  and  the  faculty  of  taste ;  both  of  which  are  abolished  by  its 
division.  It  is  probable  that  these  two  kinds  of  sensibility  reside  in 
different  nerve  fibres;  since  cases  have  been  observed  in  which  the 
sense  of  taste  is  diminished  or  lost  while  the  tactile  sensibility  of  the 
tongue  remains  unimpaired.  It  has  not  been  possible  thus  far  to  deter- 
mine the  special  source  or  location  of  the  two  functions  in  the  lingual 
nerve ;  but  it  is  evident  that  the  exercise  of  taste  is  facilitated  by  the 
general  sensibility  of  the  tongue,  and  is  influenced  by  the  condition 
of  the  local  circulation  and  the  buccal  secretions.  When  the  tongue 
is  dry  and  coated  from  febrile  action  the  taste  is  either  abolished  or 
replaced  by  morbid  sensations.  It  depends  therefore  for  iis  exercise. 
not  only  on  tin-  .-jM-cial  ^eligibility  of  the  lingual  nerve,  hut  also  on  all 
the  condition-  requisite  for  the  integrity  of  the  mucous  membrane. 

Influence  on  the  Sense  of  Hear in< i . — The  influence  of  the  fifth  pair 
on  the  perception  of  ><>imd  i>  tofl  distinct  than  in  regard  to  the  other 
.-pccial  sen.-e.-,  mid  i>  only  surmised  from  its  anatomical  relations.  It 
provides  for  the  --eneral  -eligibility  of  the  external  ear  l»y  twi.irs  from 


THE    CRANIAL    NERVES.  467 

its  auriculo-temporal  branch,  which  supply  the  anterior  border  of  the 
concha  and  the  anterior  wall  of  the  external  auditory  meatus.  Its 
relation  with  the  deeper  parts  of  the  organ  is  established  through  the 
otic  ganglion  of  the  sympathetic,  which  receives  a  few  fibres  from  its 
inferior  maxillary  division,  and  sends  a  filament  backward  to  the  plexus 
on  the  inner  surface  of  the  membrane  of  the  tympanum.  This  plexus  is 
also  supplied  with  filaments  from  the  ganglion  of  the  glosso-pharyngeal 
nerve ;  and  is  consequently  made  up  of  fibres  from  both  these  sources. 
Its  sensitive  fibres  terminate  in  the  lining  membrane  of  the  middle  ear. 
The  secretions,  both  of  this  cavity  and  of  the  external  auditory  meatus, 
are  important  for  the  preservation  of  the  integrity  of  the  parts  and  for 
the  mechanism  of  audition  ;  and  a  considerable  portion  of  their  nervous 
supply  is  derived  from  the  fifth  pair. 

Sixth  Pair.    The  Abducens. 

The  abducens  nerve,  so  called  because  it  is  distributed  to  the  single 
muscle  causing  abduction  of  the  eyeball,  originates  mainly  from  a 
deposit  of  gray  substance  on  the  floor  of  the  fourth  ventricle  near  its 
widest  part,  at  a  point  corresponding  with  the  posterior  border  of  the 
pons  Varolii.  It  is  situated  next  the  median  line,  and  is  indicated 
on  each  side  by  a  longitudinal  prominence,  known  as  the  "  fasciculus 
teres."  This  nucleus  is  designated  as  the  common  nucleus  of  the 
abducens  and  facial  nerves  ;  since  the  root  fibres  of  both  these  nerves 
are  traced,  through  somewhat  different  routes,  to  its  gray  substance. 
The  fibres  of  the  abducens,  as  shown  by  Dean,  Meynert,  and  Henle, 
originate  from  the  inner  border  of  the  nucleus  without  apparent  decus- 
sation  with  those  of  the  opposite  side.  They  pass  almost  directly  down- 
ward and  forward,  through  the  tuber  annulare,  to  their  emergence  at 
the  base  of  the  brain,  at  the  posterior  edge  of  the  pons  Yarolii.  From 
this  point,  the  nerve,  which  is  about  two  millimetres  in  thickness,  runs 
forward,  beneath  the  pons,  passing,  in  company  with  the  oculomotorius 
and  patheticus,  along  the  wall  of  the  cavernous  sinus  and  through  the 
sphenoidal  fissure,  to  the  cavity  of  the  orbit,  where  it  terminates  in  the 
external  straight  muscle  of  the  eyeball. 

Physiological  Properties  of  the  Abducens. — By  the  experiments  of 
Longet  on  rabbits,  and  those  of  Chauveau  on  rabbits  and  horses,  the 
abducens  is  shown  to  be,  at  its  origin,  exclusively  a  motor  nerve ;  since 
its  irritation  in  this  region  produces  contraction  of  the  external  straight 
muscle  of  the  eyeball,  without  any  indication  of  sensibility.  According 
to  Longet,  the  difference  in  this  respect  between  the  abducens  and  the 
trigeminus  is  very  marked ;  irritation  of  the  trigeminus  always  giving 
rise  to  signs  of  acute  sensibility,  while  that  of  the  abducens  has  no 
other  effect  than  local  muscular  contraction. 

Division  of  this  nerve  causes  internal  strabismus  from  paralysis  of 
the  external  straight  muscle,  and  loss  of  the  power  of  horizontal  rotation 
of  the  eyeball ;  while  its  vertical  movements  are  still  preserved,  owing 
to  the  continued  activity  of  the  oculomotorius  nerve.  There  are  cases 


468  THE    NERVOUS    SYSTEM. 

of  internal  strabismus,  in  man,  accompanied  by  the  above  symptoms, 
apparently  due  to  compression  of  tin-  abducens  nerve  within  the  cranial 
cavity. 

Seventh  Pair.     The  Facial. 

In  the  innervation  of  the  external  parts  of  the  face,  this  nerve  holds 
an  equal  rank  with  the  fifth  pair,  and  may  be  regarded  as  complementary 
to  it  in  physiological  endowments.  As  the  trigeminus  is  the  nerve  of 
sensation  for  the  integument  of  this  region,  the  facial  is  the  motor 
nerve  for  its  superficial  muscles.  It  is  the  nerve  of  expression,  by 
which  the  features  are  animated  in  their  varying  movements,  corre- 
sponding with  the  different  phases  of  mental  or  emotional  activity. 
Although  at  its  origin  an  exclusively  motor  nerve,  it  receives,  soon  after 
its  emergence  from  the  cranium,  a  communicating  branch  from  the  fifth 
pair,  which  gives  to  it,  and  to  the  muscles  in  which  it  terminates,  a 
certain  share  of  sensibility. 

The  facial  nerve  has  its  principal  source  in  a  collection  of  gray  sub- 
stance, already  described  as  giving  origin  to  the  abducens  (page  467). 
The  fibres  of  the  abducens  and  facial  nerves  are  given  off  from  its 
internal  and  external  borders  respectively ;  those  of  the  abducens  passing 
directly  downward  through  the  tuber  annulare,  near  the  median  plane, 
those  of  the  facial  first  passing  outward  and  then  bending  downward, 
to  their  point  of  emergence  at  the  lateral  part  of  the  posterior  edge  of 
the  pons  Varolii. 

According  to  Dean,  Meynert,  and  Henle,  a  considerable  portion  of  the 
root  fibres  of  the  facial  nerve  communicate,  either  directly  or  through 
the  nucleus,  across  the  median  line,  with  the  opposite  side  of  the  brain. 

After  emerging  from  the  edge  of  the  pons  Yarolii,  the  facial  nerve, 
in  company  with  the  auditory,  passes  into  and  through  the  internal 
auditory  meatus.  It  thence  enters  the  aqueduct  of  Fallopius,  and,  fol- 
lowing the  course  of  this  canal  through  the  petrous  portion  of  the 
temporal  bone,  comes  out  at  the  stylomastoid  foramen  and  turns  forward 
upon  the  side  of  the  face.  It  spreads  out  between  the  lobules  of  the 
parotid  gland  in  a  number  of  branches,  which,  by  mutual  interlacement, 
form  the  well-known  "parotid plexus,"  or  "pesanserinus,"  of  thisnerve. 
Its  branches  thence  diverge  upward,  forward,  and  downward,  to  the 
superficial  muscles  of  the  facial  region.  It  also  supplies,  by  branches 
given  off  immediately  after  its  emergence  from  the  stylomastoid  fora- 
men, the  muscles  of  the  external  ear,  as  well  as  the  stylohyoid  and  the 
posterior  belly  of  the  digastric;  and  by  a  twig  which  descends  to  the 
submaxillary  region,  it  supplies  filaments  to  the  upper  part  of  the 
platysma  myoides,  and  communicates  with  an  ascending  branch  of  the 
superficial  cervical  nerve  from  the  cervical  plexus. 

Physiological  Properties  of  the  Facial  Nerve. — The  facial  i>  shown. 
by  the  result  of  abundant  investigations,  to  be,  at  its  origin  and  in  its 
main  physiological  characters,  a  motor  nerve.  Not  only  is  the  tactile 
sensibility  of  the  facial  region  completely  destroyed  by  section  of  the 


THE    CRANIAL    NERVES. 


469 


trigeminus,  though  the  facial  remain  uninjured,  but,  according  to  both 
Magendie  and  Bernard,  the  trunk  of  the  facial,  when  irritated  at  its 
source  within  the  cranial  cavity,  exhibits  no  sign  of  sensibility,  although 
that  of  the  fifth  pair  may  be  at  the  same  time  perfectly  manifest.  On 
the  other  hand,  Chauveau  has  found  that  in  the  recently  killed  animal, 
galvanization  of  the  intracranial  portion  of  the  facial  nerve  causes  con- 
traction of  the  muscles  of  the  face  and  of  the  external  ear.  The  nerve 
is  accordingly,  at  its  source,  excitable,  but  insensible. 

FIG.  124. 


DIAGRAM  OF  THE  FACIAL  NERVE  AND  ITS  DISTRIBTTTION.— 1.  Facial  nerve  at  Its  entrance  Into  the 
internal  auditory  meatus.  2.  Its  exit,  at  the  stylomastoid  foramen.  3,  4.  Temporal  and  posterior 
auricular  branches,  distributed  to  the  muscles  of  the  external  ear  and  to  the  occipitalis.  5. 
Branches  to  the  frontalis  muscle.  6.  Branches  to  the  stylohyoid  and  digastric  muscles.  7.  Branches 
to  the  upper  part  of  the  platysma  myoides.  8.  Branch  of  communication  with  the  superficial 
cervical  nerve  of  the  cervical  plexus. 

Furthermore,  the  most  decisive  results  are  obtained  from  division  of 
the  facial  nerve  at  various  parts  of  its  course.  This  may  be  done,  in 
quadrupeds,  at  its  point  of  exit  from  the  stylomastoid  foramen,  or, 
as  practised  by  Bernard,  during  its  passage  through  the  aqueduct  of 
Fallopius,  by  a  cutting  instrument  introduced  into  the  cavity  of  the 
tympanum,  and  reaching  the  nerve  through  its  upper  wall.  This  sec- 
tion paralyzes  all  the  superficial  muscles  of  the  face  on  the  corresponding 


470  f  H  K     N  I-:  II  V  0  I  r  S     S  Y  S  T  K  M  . 

side.  The  visible  effects  vary  in  tho  different  facial  regions,  according 
t<»  the  function  of  tlie  paraly/ed  muscles. 

Effect  <>n  tin'  /'Ji/e.— Owing  to  paralysis  of  the  orbicularis  oculi,  the 
eve  on  the  affected  side  cannot  be  closed;  according  to  Bernard  it  re- 
mains open  even  while  the  animal  is  asleep.  This  depends  on  the  fact 
that  tin-  muscles  serving  to  open  and  close  the  eyelids  are  animated  by 
different  nerves;  the  levator  palpebrae  superioris,  which  lifts  the  upper 
eyelid,  beinir  supplied  by  the  oculomotorius,  while  the  orbicularis  oculi 
receives  its  filaments  from  the  facial.  In  paralysis  of  the  facial,  there- 
fore, complete  closure  of  the  lids  is  impossible,  although  the  movements 
of  the  eyeball  and  pupil  are  unaffected. 

At  the  same  time  the  movement  of  winking  is  suspended  on  the 
affected  side.  This  is  a  reflex  action,  caused  by  the  contact  of  air  with 
the  surface  of  the  cornea,  and  the  accumulation  of  tears  along  the  edge 
of  the  lower  eyelid.  At  short  intervals  this  excites  a  momentary  con- 
traction of  the  orbicularis,  by  which  the  eyelids  are  brought  together, 
and  again  immediately  separated;  thus  spreading  the  lachrymal  secre- 
tion uniformly  over  the  cornea  and  protecting  it  from  desiccation. 
After  section  of  the  facial  nerve,  this  movement  ceases;  and  if  a  solid 
body  lie  suddenly  thrust  toward  the  face  of  the  animal,  the  eye  on  the 
sound  side  instinctively  closes,  while  the  other  remains  open.  Even 
touching  the  cornea  on  the  operated  side  fails  to  cause  contraction  of 
the  eyelids,  although  the  animal  shrinks  and  the  eyeball  turns  in  its 
orbit;  showing  that  sensibility  remains,  although  the  motor  power  of 
the  orbicularis  is  lost. 

Precisely  opposite  effects,  accordingly,  are  produced  by  section  of  the 
fifth  nerve,  and  by  that  of  the  facial.  After  division  of  the  fifth,  touch- 
ing the  cornea  fails  to  produce  closure  of  the  eyelids  because  the  sensi- 
bility of  the  surface  has  been  destroyed,  though  the  power  of  motion 
remains.  When  the  facial  has  been  'divided,  muscular  action  is  para- 
lyzed, and  sensibility  remains  entire. 

Effect  on  the  Nostrils. — In  man,  as  well  as  in  some  animals,  the 
nostrils  are  nearly  motionless  in  the  ordinary  state  of  respiration.  They 
expand,  however,  with  considerable  vigor  when  the  breathing  is  in- 
creased in  frequency,  or  when  the  air  is  forcibly  inspired  to  assist  the 
e  of  smell;  and  in  many  quadrupeds  they  exhibit  regular  move- 
ments of  expansion  and  collapse,  synchronous  with  those  of  the  chest 
and  abdomen.  In  man,  this  action  becomes  very  marked  whenever 
the  breathing  is  hurried  or  laborious,  owing  to  muscular  exertion  or 
obstruction  of  the  air-passages. 

These  movements  are  suspended  by  section  of  the  facial  nerve.  The 
ril  on  the  affected  side  becomes  flaccid,  and,  instead  of  opening 
for  the  admission  of  air,  it  collapses  and  forms  an  obstruction  to  its 
entrance.  As  the  dyspmra  thus  induced  tends  to  accelerate  respiration, 
the  paralyzed  nostril  is  still  further  compressed  in  inspiration;  and  at 
expiration  it  is  forcibly  extruded  by  the  outgoing  current.  The  natural 
movements  of  the  nostril  are  therefore  reversed  by  paralysis  of  the 


THE    CRANIAL    NERVES.  471 

facial  nerve.  In  the  normal  condition  it  expands  in  inspiration,  and 
partially  collapses  in  expiration.  But  after  section  of  the  nerve  it  col- 
lapses in  inspiration,  and  partially  opens  in  expiration;  moving  pas- 
sively, like  an  inert  valve,  with  the  changing  direction  of  the  air 
current. 

Effect  on  the  Lips. — In  animals,  and  especially  in  the  herbivora,  the 
movements  of  the  lips  serve  mainly  for  prehension  of  the  food ;  and  if 
they  be  paralyzed  on  both  sides,  the  consequent  incapacity  to  introduce 
food  into  the  mouth  may  be  sufficient  to  cause  death  by  inanition.  In 
the  carnivora  the  retraction  and  elevation  of  the  lips,  by  which  the 
canine  teeth  are  uncovered,  have  a  marked  effect  on  the  expression  of 
the  face ;  and  in  most  animals,  after  division  of  the  facial  nerve,  the 
change  of  appearance  in  the  corresponding  side,  even  in  the  quiescent 
condition,  is  distinctly  perceptible.  The  lips  are  inactive,  and  the 
corner  of  the  mouth  hangs  down  partly  open,  owing  to  paralysis  of 
the  orbicularis  oris. 

Effect  on  the  Ears. — In  many  quadrupeds  the  external  ears  are 
more  important  than  in  man,  owing  to  their  greater  development  and 
superior  mobility.  Their  varying  position  has  great  influence  in 
modifying  the  expression;  and  their  rapid  and  extensive  movements 
are  of  essential  aid  in  the  sense  of  hearing.  When  the  facial  nerve 
has  been  divided,  the  ear  on  the  corresponding  side  becomes  motion- 
less; and  if  long  and  narrow,  as  in  the  rabbit,  it  can  no  longer 
maintain  the  erect  position. 

Facial  Paralysis  in  Man. — Facial  paralysis,  from  disease  involving 
the  trunk  of  the  nerve,  or  its  sources  in  the  brain,  is  not  an  uncom- 
mon affection  in  man.  It  is  usually  confined  to  one  side,  being  limited 
by  the  median  line,  and  producing  a  difference  of  expression  on  the  two 
sides  of  the  face.  Where  the  difficulty  is  located  in  particular  branches 
of  the  nerve,  certain  portions  of  the  face  may  be  affected  to  the  exclu- 
sion of  others.  The  lips  may  be  paralyzed  without  loss  of  motion  in 
the  parts  above,  and  vice  versa  ;  or  the  affection  may  be  fully  developed 
in  one  region,  and  only  partial  in  the  remainder.  But  when  the  dis- 
ease is  seated  on  the  trunk  of  the  nerve,  within  the  aqueduct  of  Fal- 
lopius,  or  involves  its  central  origin,  its  consequences  extend  uniformly 
over  one  side,  forming  a  complete  unilateral  facial  paralysis. 

The  signs  of  facial  paralysis  in  man  are,  in  general,  those  which  fol- 
low experimental  division  of  this  nerve  in  animals.  Its  main  peculiar- 
ity depends  on  the  greater  development,  in  man,  of  the  facial  muscles 
as  organs  of  expression ;  and  its  most  marked  effect  is  consequently 
loss  of  expression  on  the  paralyzed  side.  All  the  features  have  a  col- 
lapsed appearance.  The  eyelids  are  motionless,  the  eye  remains  con- 
stantly open,  and  the  lower  lid  sinks  below  the  level  of  the  cornea ; 
thus  giving  to  the  eye  a  staring,  vacant  appearance.  The  act  of  wink- 
ing is  no  longer  performed  on  the  affected  side.  Owing  to  the  paralyzed 
condition  of  the  frontalis  and  superciliary  muscles,  all  the  characteristic 
lines  and  wrinkles  on  this  side  disappear,  and  the  forehead  and  eyebrow 


472 


T  H  E     N  !•;  II  V  O  L  S    S  Y  S  T  E  M  . 


become  smooth  and  expressionless.  The  same  is  true  of  the  cheek, 
which,  as  well  as  the  nostril,  is  flattened  and  collapsed.  The  corner 
of  the  mouth  hanirs  downward,  and  owing  to  imperfect  closure  of 
the  lips  there  is  sometimes  a  continual  escape  of  saliva  from  this  point. 
Beside  these  symptoms  there  is  also  a  deviation  of  the  mouth  toward 
the  sound  side,  owing  to  the  facial  muscles  on  that  side  being  no  longer 
antagonized  by  the  opposite.  In  many  instances  this  deviation  is  not 
observable  during  a  state  of  quiescence,  both  sets  of  muscles  being 
habitually  relaxed;  and  it  becomes  evident  only  when  the  patient 
uses  those  of  the  sound  side,  as  in  speaking,  whistling,  or  laughing, 
or  when  the  emotions  are  excited.  But  in  cases  where  the  face  has 
naturally  an  abundance  of  expression,  the  distortion  of  the  features, 

FIG.  125. 


FACIAL  PARALYSIS  of  the  right  si<l<>. 

and  their  different  appearance  on  the  two  sides,  are  distinct  at  all 
times,  becoming  still  more  marked  when  the  patient  is  excited  or 
engaged  in  conversation. 

Another  effect  of  facial  paralysis  in  man  is  difficulty  in  drinking  and 
in  mastication.  The  difficulty  in  drinking  is  due  to  deficient  action  of 
the  orbieularis  oris  on  the  affected  side;  so  that  the  lips  at  this  corner 
of  the  mouili  cannot  be  kept  in  contact  with  the  sides  of  the  goblet. 


THE    CRANIAL    NERVES.  473 

The  fluid  consequently  escapes  and  runs  over  the  lower  part  of  the 
face,  unless  the  patient  aids  the  paralyzed  part  by  pressure  with  the 
fingers.  The  difficulty  in  mastication  results  from  paralysis  of  the 
buccinator  muscle,  and  the  relaxed  condition  of  the  cheek.  The  food 
consequently  lodges  between  the  gum  and  the  cheek ;  and  the  patient 
is  often  obliged  to  remove  it  by  mechanical  means  in  order  to  complete 
its  mastication. 

The  loss  of  power  in  the  orbicularis  also  produces  imperfect  articu- 
lation. The  lips  cannot  be  brought  together  with  precision,  and  the 
labials,  such  as  B  and  P,  are  imperfectly  pronounced.  In  cases  of  bilat- 
eral paralysis,  which  have  been  sometimes  observed,  the  features  are  no 
longer  deviated  from  their  symmetrical  position,  but  the  difficulty  of 
articulation  is  much  increased,  extending  to  some  of  the  vowels,  such 
as  0  and  U,  which  require  contraction  of  the  orbicularis  oris.  This 
affection  is  distinct  from  that  known  as  "  glosso-labio-laryngeal  paraly- 
sis "  (page  445),  in  which  articulation  is  also  impaired.  In  the  latter 
disease,  which  is  of  central  origin,  the  paralysis  affects  the  muscles  of 
the  tongue  and  larynx,  as  well  as  those  of  the  lips ;  in  facial  paralysis 
it  is  confined  to  those  which  receive  their  filaments  from  the  seventh 
pair.  Facial  paralysis  may  therefore  exist  without  danger  to  life. 

Crossed  Action  of  the  Facial  Nerve. — Minute  examination  of  the 
origin  of  this  nerve  indicates  a  transverse  communication  by  decus- 
sating fibres,  between  its  nucleus  on  the  floor  of  the  fourth  ventricle 
and  the  opposite  side  of  the  tuber  annulare.  It  has  not  yet  been  found 
possible,  however,  to  follow  these  fibres  throughout,  or  to  decide  whether 
they  are  root  fibres  which  have  simply  passed  through  the  nucleus,  or 
whether  they  originate  from  the  nerve  cells  of  the  nucleus  and  thence 
pass  to  the  opposite  side. 

That  the  facial  nerve  has  in  great  part  a  crossed  action  is  evident 
from  the  results  of  pathological  observation.  Facial  paralysis  is  a  fre- 
quent accompaniment  of  hemiplegia;  and  in  the  great  majority  of 
instances,  that  is,  when  the  cerebral  lesion  is  above  the  tuber  annulare, 
the  hemiplegia  of  the  body  and  limbs  and  the  paralysis  of  the  face  are 
on  the  same  side  with  each  other.  The  injury  to  the  brain,  therefore, 
in  such  cases,  produces  both  hemiplegia  and  facial  paralysis  on  the 
opposite  side.  But  when  the  injury  is  lower  down,  in  the  tuber  annu- 
lare, it  may  affect  at  the  same  time  the  roots  of  the  facial  nerve  outside 
its  nucleus,  and  the  anterior  pyramids  above  their  decussation ;  caus- 
ing in  this  way  a  facial  paralysis  on  the  same  side  and  hemiplegia  on 
the  opposite  side.  It  thus  appears  that  the  facial  paralysis  is  on  the 
side  of  the  cerebral  lesion  when  this  is  below  the  nucleus,  and  on  the 
opposite  side  when  it  is  above  the  nucleus  or  in  the  hemispheres.  This 
shows  that  the  action  of  the  facial  nerve  is  largely  a  crossed  action. 

The  cross  connection,  however,  between  the  nucleus  and  the  opposite 
side  of  the  brain  does  not  affect  all  the  functions  of  this  nerve.  The 
only  decussation  of  its  fibres  known  to  exist  is  that  which  takes  place  at 
the  raphe  on  the  floor  of  the  fourth  ventricle.  If  all  the  fibres  of  the 


474  THK    NERVOUS     SYSTEM. 

nerve  root  crossed  at  this  point,  n  longitudinal  section  at  the  median 
line  between  the  two  nuclei  would  completely  paralyze  both  sides  of 
the  face.  But  this  effect  is  not  produced;  since  in  the  experiments 
of  Vulpian,*  on  dogs  and  rabbits,  the  animals  after  this  operation  were 
still  capable  of  winking-  with  both  eyes ;  only  the  action  was  no  longer 
simultaneous,  each  eye  being  closed  at  irregular  intervals  independently 
of  the  other. 

It  is  evident,  therefore,  that  the  reflex  action,  in  winking,  takes 
place  for  each  eye  on  the  same  side,  no  doubt  in  the  gray  substance 
of  the  facial  nucleus;  the  two  nuclei  habitually  acting  in  harmony  by 
means  of  their  conimissural  fibres.  But  the  voluntary  and  emotional 
impulses,  which  cause  movement  of  the  features,  are  transmitted  by 
decussating  fibres  from  opposite  sides  of  the  brain. 

This  is  still  further  indicated  by  the  effects  of  peripheral  and  central 
lesions  of  the  nerve.  In  man,  as  well  as  in  animals,  if  this  nerve  be 
divided  or  destroyed  during  its  passage  through  the  aqueduct  of 
Fallopius,  all  the  facial  movements  are  paralyzed  together.  But  in 
paralysis  depending  on  a  cerebral  lesion  above  the  nucleus,  it  is  gen- 
erally observed  that  the  loss  of  motion  is  not  complete ;  but  that, 
while  all  other  movements  of  the  face  are  paralyzed,  the  action  of 
winking  remains  on  the  affected  side.  This  peculiarity  is  used  as  a 
means  of  diagnosis  between  facial  paralysis  from  injury  of  the  nerve 
and  that  caused  by  a  lesion  in  the  brain. 

Sensibility  of  the  Facial  Nerve. — Although  this  nerve  is  exclusively 
motor  at  its  origin,  it  subsequently  receives  filaments  of  communication 
from  the  trigeminus,  which  give  it  a  certain  degree  of  sensibility.  The 
most  important  of  these  branches,  given  off  from  the  inferior  maxillary 
division  of  the  fifth  nerve,  joins  the  facial  soon  after  its  emergence  from 
the  stylomastoid  foramen,  and  thence  accompanies  its  principal  rami- 
fications. According  to  the  united  testimony  of  modern  experimenters, 
the  facial  nerve,  if  examined  on  the  side  of  the  face,  is  found  sensi- 
tive to  mechanical  irritation,  although  its  sensibility  is  much  inferior 
to  that  of  the  tilth  pair.  Owing  to  this  communication,  the  neuralgic 
pain  of  tic  douloureux  sometimes  seems  to  follow  the  horizontal 
branches  of  the  facial  nerve.  The  proof,  however,  that  its  sensitive 
fibres  are  derived  from  anastomosis  and  do  not  originally  form  part 
of  its  trunk,  is  that  the  sensibility  of  the  regions  to  which  it  is  distrib- 
uted disappears  completely  after  division  of  the  iifth  pair,  notwith- 
standing that  the  facial  remains  entire. 

Beside  the  communication  above  mentioned,  this  nerve  contracts 
frequent  anastomoses,  in  the  anterior  part  of  the  face,  with  the  supra- 
orbital,  infraorbital,  and  mental  branches  of  the  fifth  pair. 

Communication*  <>f  the  Facial  Nerve  in  the  Aqueduct  of  Fallujiiua. 
— While  passing  through  its  canal  in  the  petrous  portion  of  the  temporal 
bone,  the  facial  nerve  gives  off  a  number  of  slender  filaments  by  which 


i  la  Physiologic  du  SystC-me  Nerveux.     Paris,  1866,  p.  480. 


THE    CRANIAL    NERVES. 


475 


it  communicates  with  other  nerves  or  with  ganglia  of  the  sympathetic 
system.  The  physiological  character  of  most  of  these  filaments  is  im- 
perfectly understood ;  but 
they  are  of  interest  from 
being  usually  involved  in 
injury  of  the  nerve  within 
its  bony  canal,  thus  pro- 
ducing secondary  symp- 
toms, in  addition  to  those 
of  facial  paralysis. 

At  the  elbow  formed  by 
the  anterior  bend  of  the 
facial  nerve,  soon  after  its 
entrance  into  the  aqueduct 
of  Fallopius,  there  is  a 
small  collection  of  gray 
substance,  known  as  the 

"  o-ano-linn       rrpniVnlitiim  "    THE  FACIAL  NKRVE  AND  ITS  CONNECTIONS,  within  the 

aqueduct  of  Fallopius.-l.  Fifth  nerve,  with  the  Gas- 
serian  ganglion.  2.  Ophthalmic  division  of  the  fifth 
nerve.  3.  Superior  maxillary  division  of  the  fifth  nerve. 
4.  Lingual  nerve.  5.  Sphenopalatine  ganglion.  6.  Otic 
ganglion.  7.  Submaxillary  ganglion.  8.  Facial  nerve  in 
the  aqueduct  of  Fallopius.  9.  Great  superficial  petrosal 
nerve.  10.  Small  superficial  petrosal  nerve.  11.  Stape- 
dius  hranch  of  facial  nerve.  12.  Branch  of  communica- 
tion with  pneumogastric  nerve.  13.  Branch  of  communi- 
cation with  glossopharyngeal  nerve.  14.  Chorda  tympani. 


From  this  ganglion  a  slen- 
der filament,  the  great  su- 
perficial petrosal  nerve 
(Fig.  126, 9),  runs  obliquely 
forward  through  the  base 
of  the  skull,  and  terminates 
in  the  sphenopalatine  gan- 
glion (5).  This  ganglion,  which  is  also  connected  with  the  superior 
maxillary  division  of  the  fifth  nerve  (3),  sends  branches  to  the  mucous 
membrane  of  the  posterior  part  of  the  nasal  passages  and  the  hard  and 
soft  palate,  and  to  the  levator  palati  and  uvular  muscles ;  that  is,  to 
the  dilators  of  the  isthmus  of  the  fauces. 

This  filament  of  communication  between  the  facial  nerve  and  the 
sphenopalatine  ganglion,  is  no  doubt  the  motor  root  of  the  ganglion, 
supplying  motive  force  for  its  muscular  branches.  Such  an  inference 
seems  justified  by  the  affection  of  the  palatal  muscles  accompanying 
certain  cases  of  facial  paralysis  from  deep-seated  lesions.  It  consists  in 
an  incapacity  to  lift  the  soft  palate,  which  hangs  passively  downward, 
and  in  a  lateral  deviation  of  the  uvula,  which,  according  to  Longet,  is 
always  toward  the  sound  side.  The  levator  palati  and  uvular  muscles 
being  paralyzed,  the  uvula  is  drawn  into  an  oblique  position  toward 
the  non-paralyzed  side.  As  there  is  no  other  communication  between 
the  facial  nerve  and  the  palatal  muscles  than  that  through  the  spheno- 
palatine ganglion  by  the  great  superficial  petrosal  nerve,  the  latter 
must  be  regarded  as  containing  motor  fibres  running  from  the  facial 
to  the  ganglion. 

A  little  below  the  last-mentioned  filament,  the  facial  nerve  gives  off 
a  second,  the  small  superficial  petrosal  nerve  (10),  which  communicates 
both  with  the  otic  ganglion  and  with  the  plexus  on  the  inner  wall  of 


476  THE    NERVOUS    SYSTEM. 

the  tympanum,  known  as  tho  "tympanic  plexus,"  which  supplies  the 
lining  membrane  of  the  tympanic  cavity,  while  the  otic  ganglion  sends 
a  motor  filament  to  the  tensor  tymparii  muscle. 

From  the  concave  border  of  the  facial  nerve,  as  it  bends  downward, 
a  fine  motor  filament,  the  xtapedius  branch  („),  passes  forward  to  the 
stapedius  muscle.  The  facial,  therefore,  in  this  part  of  its  course,  has 
an  influence  on  the  mechanism  of  hearing,  through  the  muscles  which 
regulate  the  tension  of  the  membrana  tympani.  This  influence  is 
exerted  direetlv  bv  its  stapedius  branch,  and  indirectly,  through  the 
otic  ganglion,  by  the  filament  supplied  to  the  tensor  tympani.  Facial 
paralysis  is  sometimes  accompanied  by  partial  deafness,  and  sometimes 
bv  abnormal  sensibility  to  sonorous  impressions;  but  it  has  not  been 
determined  how  far  these  symptoms  are  due  to  paralysis  of  the  muscles 
of  the  middle  ear,  or  to  the  implication  of  other  parts. 

From  its  descending  portion,  the  facial  nerve  gives  off  two  small 
branches  of  communication  (12,M),  one  to  the  pneumogastric  and  one  to 
the  glossopharyngeal  nerve,  both  of  which  are  usually  considered  as 
motor  filaments.  This  seems  nearly  certain  in  regard  to  the  glosso- 
pharyngeal branch ;  since  Cruveilhier  describes  a  separate  filament  of 
the  facial  sometimes  passing  to  the  styloglossal  and  palatoglossal  mus- 
cles, and  Longet  cites  an  instance  in  which  a  branch  of  the  facial,  on 
one  side,  without  making  connection  with  the  glossopharyngeal  nerve, 
was  distributed  directly  to  the  palatoglossal  and  glossopharyngeal  mus- 
cles; that  is,  to  the  constrictors  of  the  isthmus  of  the  fauces. 

Finally  the  facial  nerve,  shortly  before  its  exit  from  the  stylomastoid 
foramen,  gives  off  from  its  concave  border  the  chorda  tympani  d4). 
It  first  passes  in  a  recurrent  direction,  traverses  the  cavity  of  the  tym- 
panum near  the  inner  surface  of  the  membrana  tympani,  curves  down- 
ward and  forward,  and  at  last  joins  the  descending  portion  of  the 
lingual  nerve.  Some  of  its  fibres  afterward  diverge,  passing  to  the 
snlmiaxillary  ganglion  and  the  submaxillary  gland;  while  others  con- 
tinue onward  with  the  lingual  nerve  and  accompany  its  distribution  in 
the  tongue. 

The  most  positive  knowledge  in  our  possession  as  to  the  physiologi- 
cal character  of  the  chorda  tympani  relates  to  its  influence  on  the  phe- 
nomena of  circulation  and  secretion  in  the  tongue  and  the  submax- 
illary gland.  The  experiments  of  Bernard,  corroborated  by  subsequent 
observers  and  especially  by  Vulpian,*  show  that  galvanization  of  the 
chorda  tympani  increases  both  the  circulation  of  the  blood  and  the 
secretion  of  saliva  in  the  submaxillary  ^land.  But  if  the  chorda  tym- 
pani br  divided  both  these  actions  suffer  diminution,  and  the  gland 
remains  inexcitable  when  a  sapid  substance  is  introduced  into  the  mouth. 
If  the  peripheral  extremity  of  the  divided  nerve  be  galvanized,  circula- 
tion and  secretion  are  excited  as  before;  and  the  same  effect  is  pro- 
duced by  M imulatin.tr,  either  the  lingual  nerve,  or  the  filament  which 


*  Leyons  aur  1'Apparcil  Vuso-moteur.     Paris?,  1875,  tome  i.,  p.  150. 


THE    CRANIAL    NERVES.  477 

it  sends  to  the  submaxillary  gland.  A  similar  influence  is  exerted  on 
the  circulation  in  the  corresponding  half  of  the  tongue ;  and  it  is  of 
special  importance  that  this  increase  of  circulatory  activity,  excited  by 
galvanizing  the  chorda  tympani  above  its  union  with  the  lingual,  is 
also  produced,  according  to  Yulpian,*  by  galvanizing  the  separated 
extremity  of  the  divided  lingual  nerve  containing  fibres  of  the  chorda 
tympani.  This  shows  that  its  influence  is  in  the  nature  of  a  motor 
action ;  that  is,  it  passes  from  the  central  parts  toward  the  periphery, 
and  not  in  the  inverse  direction.  Finally,  while  evulsion  of  the  facial 
nerve  from  the  aqueduct  of  Fallopius  arrests  the  secretive  action  of  the 
submaxillary  gland,  its  section  at  the  stylomastoid  foramen  does  not 
have  this  effect,  but  only  paralyzes  the  muscles  of  the  face.  This  dif- 
ference depends  on  the  fact  that  in  the  former  case  the  chorda  tym- 
pani is  involved  in  the  injury,  in  the  latter  it  remains  intact. 

Another  symptom  observed  in  deep-seated  lesions  of  the  facial  nerve, 
and  also  dependent  on  injury  of  the  chorda  tympani,  is  a  disturbance 
of  the  sense  of  taste  in  the  tip  and  surface  of  the  tongue.  In  this 
affection,  the  taste  is  not  absolutely  abolished,  but  is  diminished  in 
acuteness  and  in  promptitude.  If  a  bitter  substance  be  placed  alter- 
nately on  the  two  sides  of  the  tongue,  it  is  perceived  almost  imme- 
diately on  the  sound  side,  but  only  after  a  considerable  interval  on  the 
side  of  the  paralysis.  Various  explanations  have  been  suggested  for 
these  phenomena,  which  by  most  writers  are  referred  exclusively  to 
the  chorda  tympani.  As  the  fibres  of  this  nerve  have  so  marked  an 
influence  on  the  circulation  in  the  tongue  ancl  on  salivary  secretion, 
it  is  plain  that  when  these  functions  are  depressed  by  its  division  or 
injury  the  sense  of  taste  may  be  impaired  as  an  indirect  result.  But 
whatever  be  the  mechanism  of  its  action,  there  is  no  question  that  its 
paralysis  interferes,  to  an  appreciable  degree,  with  this  sense ;  and  an 
alteration  of  taste,  accompanying  facial  paralysis  on  the  same  side, 
consequently  fixes  the  location  of  the  nervous  lesion  at  some  point 
within  the  stylomastoid  foramen. 

Eighth  Pair.    The  Auditory. 

On  the  posterior  surface  of  the  medulla  oblongata,  a  little  behind  the 
widest  part  of  the  fourth  ventricle,  a  number  of  white  striations  run 
from  the  neighborhood  of  the  median  line  transversely  outward,  toward 
the  peduncles  of  the  cerebellum.  These  striations  represent  the  roots 
of  the  auditory  nerve.  The  nucleus  from  which  they  originate  is  a 
mass  of  gray  substance  beneath  them,  containing  nerve  cells  of  the 
smaller  variety.  It  extends  outward  and  upward  toward  the  white 
substance  of  the  cerebellum,  with  which  it  is  connected  by  numerous 
radiating  fibres. 

From  this  nucleus  the  root  fibres  run  almost  horizontally  outward, 
and,  uniting  with  each  other,  curve  round  the  inferior  peduncle  of  the 


Comptes  Eendus  de  1' Academic  des  Sciences.    Paris,  1879,  tome  Ixxxix.,  p.  274. 


478  THE    XEKVOT'S     SYSTEM. 

cerebellum  to  tin-  lateral  surface  of  the  medulla  at  the  lower  border 
..{'  the  pons  Yan.lii.  Some  of  them  follow  a  deeper  course,  passing 
obliquely  through  the  substance  of  the  medulla  to  the  same  point. 
They  form  the  superior  or  external  root  of  the  auditory  nerve. 

The  internal  root  consists  of  fibres  which,  according  to  Huguenin. 
may  hr  traced  backward  from  their  point  of  emergence  into  the  inferior 
peduncle  of  the  cerebellum,  where  they  meet  with  a  second  nucleus  of 
gniy  substance,  and  continue  their  course,  in  company  with  the  longi- 
tudinal fibres  of  the  peduncle,  toward  the  white  substance  of  the  cere- 
bellum. This  connection  with  the  cerebellum  is  the  main  anatomical 
peculiarity  bv  which  the  auditory  is  distinguished  from  the  other  cranial 
nerves. 

The  auditory  nerve,  formed  by  the  union  of  these  two  roots,  after 
emerging  from  the  lateral  surface  of  the  medulla  oblongata,  passes  for- 
ward and  outward,  through  the  internal  auditory  meatus,  and  termi- 
nates in  the  nervous  expansions  of  the  internal  ear. 

Physiological  Properties  of  the  Auditory  Nerve. — The  auditory 
i>  a  nerve  of  special  sense,  serving  to  communicate  the  impression  of 
sonorous  vibrations.  In  the  experiments  of  Magendie  on  dogs  and 
rabbits,  the  auditory  nerve,  when  exposed  in  the  cranial  cavity,  was 
found  insensible  to  mechanical  irritation,  although  the  roots  of  the  fifth 
pair  exhibited  at  the  same  time  an  acute  sensibility.  Its  exclusive 
distribution  to  the  internal  ear,  for  which  it  forms  the  only  nervous 
connection  with  the  brain,  leaves  no  doubt  that  its  function  is  that  of 
transmitting  to  the  centfal  organ  the  nervous  influences  which  produce 
the  sensation  of  sound. 

Tin-  remaining  cranial  nerves,  comprising  the  glossopharyngeal,  the 
pneumogastric,  and  the  spinal  accessory,  are  distributed  to  the  deeper 
parts  about  the  commencement  of  the  digestive  and  respiratory  pa- 
sages,  where  general  sensibility  is  but  slightly  developed,  and  the 
movements  are,  for  the  most  part,  involuntary.  Externally,  they  show 
a  marked  similarity  of  anatomical  arrangement,  originating  one  behind 
the  other,  in  a  continuous  line,  along  the  lateral  furrow  of  the  medulla 
oblon-ata  and  the  side  of  the  spinal  cord,  each  by  a  series  of  separate 
filaments;  and  in  such  juxtaposition  that  it  is  in  some  instances  ditti- 
cult  to  mj  \\here  the  root  fibres  of  one  terminate,  and  those  of  the 
other  begin.  Tin-  two  sensitive  nerves  belonging  to  this  group, 
namely,  the  -lossopharyngcal  and  the  pneumogastric,  have  each  a 
distinct  -an-lion,  situated  within  their  point  of  emergence  from  the 
cranium,  and  originate  from  two  continuous  nuclei  at  the  posterior 
>iirl'aee  of  the  medulla  oblongatu.  The  motor  nerve  of  the  group,  or 
the  spin.-  .ry.  originates  from  a  nucleus  of  its  own,  and  sends 

branches  of  communication  to  the  other  two.  While  these  nerves, 
therefore,  can  hardly  be  regarded  as  a  single  pair,  they  have  never- 
thele.-s  a  close  mutual  relation  both  in  anatomical  arrangement  and  in 
physiological  properties. 


THE    CRANIAL    NERVES.  479 

Ninth  Pair.     The  Glossopharyngeal. 

The  fibres  of  the  glossopharyngeal  nerve  originate  from  a  nucleus 
situated  a  little  behind  and  below  that  of  the  auditory,  and  near  the 
outer  border  of  the  fasciculus  teres,  by  which  it  is  separated  from  the 
median  line.  The  root-fibres,  after  leaving  the  nucleus,  pass  downward 
and  outward  through  the  medulla,  and  emerge  from  its  lateral  surface, 
next  behind  the  auditory  nerve,  in  a  series  of  five  or  six  filaments,  which 
soon  unite  into  a  single  cord.  The  nerve  then  passes  into  and  through 
the  jugular  foramen,  in  company  with  its  associated  nerves,  the  pneumo- 
gastric  and  spinal  accessory.  In  this  situation  it  presents  a  ganglionic 
enlargement,  known  as  the  petrosal  ganglion,  from  its  occupying  a 
shallow  depression  in  the  petrous  portion  of  the  temporal  bone.  It 
here  gives  off  a  small  branch,  the  "  nerve  of  Jacobson,"  which  is  dis- 
tributed to  the  lining  membrane  of  the  tympanum  and  Eustachian 
tube,  and  sends  a  filament  of  communication  to  the  otic  ganglion  of 
the  sympathetic.  The  trunk  of  the  glossopharyngeal  nerve  then  passes 
downward  and  forward,  receiving  branches  of  communication  from  both 
the  facial  and  the  pneumogastric  nerves,  after  which  it  separates  into 
two  main  divisions,  one  of  which  is  destined  for  the  tongue,  the  other 
for  the  pharynx ;  a  double  distribution,  to  which  the  nerve  owes  its 
name.  The  portion  passing  to  the  tongue  is  distributed  to  the  mucous 
membrane  of  the  posterior  third  of  this  organ,  namely,  to  that  portion 
situated  behind  the  Y-shaped  row  of  circumvallate  papillaB,  and  to  these 
papillaB ;  it  also  supplies  filaments  to  the  tonsils  and  to  the  mucous 
membrane  of  the  pillars  of  the  fauces  and  the  soft  palate.  The  re- 
maining portion  of  the  nerve  is  distributed  to  the  mucous  membrane 
of  the  pharynx  and  to  the  digastric  and  stylopharyngeal  muscles,  by 
junction  with  a  branch  of  the  facial  to  the  styloglossal  muscle,  and  by 
junction  with  branches  of  the  pneumogastric  to  the  superior  and  middle 
constrictor  muscles  of  the  pharynx.  The  muscles,  accordingly,  to  which 
this  nerve  is  directly  or  indirectly  distributed  are  those  by  which  the 
tongue  is  drawn  backward  (styloglossal),  the  larynx  and  pharynx  ele- 
vated (digastric  and  stylopharyngeal),  and  the  upper  part  of  the  pharynx 
contracted  (superior  and  middle  constrictors) ;  that  is,  those  concerned 
in  the  act  of  deglutition. 

Physiological  Properties  of  the  Glossopharyngeal. — The  glossopha- 
ryngeal is  for  the  most  part  a  nerve  of  sensibility.  Its  origin  from 
the  gray  substance  in  the  medulla  oblongata  corresponding  to  the  pos- 
terior horns  of  the  spinal  cord,  the  ganglion  located  upon  its  trunk 
in  the  jugular  foramen,  and  its  principal  distribution  to  the  mucous 
membranes  of  the  tongue  and  pharynx,  all  indicate  its  anatomical  re- 
semblance to  other  sensitive  nerves  or  nerve  roots.  The  result  of 
direct  experiment  corroborates  this  view.  Longet,  in  irritating  the 
glossopharyngeal  nerve  within  the  cranium,  was  never  able  to  pro- 
duce muscular  contraction  ;  and  although  Chauveau,  in  experimenting 
upon  this  nerve  in  the  same  situation  in  recently  killed  animals,  saw 


480  THE     XERVOUS    SYSTEM. 

its  galvanization  followed  by  contraction  of  the  upper  part  of  the 
pharynx,  this  effect  was  probably  due  to  reflex  action,  since  the  nerve 
was  still  in  connection  with  the  medulla  oblougata.  This  conclusion 
is  rendered  certain  by  the  investigations  of  Reid,*  who  found  that 
irritation  of  the  glossopharyngeal  nerve  produced  movements  of  the 
throat  and  lower  part  of  the  face;  but  these  movements  wore  also  pro- 
duced, after  the  nerve  had  been  divided,  by  irritation  of  its  cranial 
extremity.  Its  sensibility,  however,  appears  to  be  of  a  low  »Tade, 
as  compared  with  that  of  the  trigeminal  nerve.  While  some  ob- 
servers (Reid)  found  its  irritation,  outside  the  jugular  foramen,  give 
ri>e  to  indications  of  pain,  others  (Panizza)  have  failed  to  elicit  by 
this  means  any  signs  of  sensibility  whatever;  and  others  still  (Longet) 
speak  of  them  in  an  uncertain  manner.  This  variation  in  the  observed 
results  is  sufficient  to  show  the  inferior  capacity  of  the  glossopharyngeal 
nerve  for  painful  impressions ;  since  no  experimenter  has  ever  doubted 
the  acute  sensibility  of  the  fifth  pair. 

But  notwithstanding  the  comparative  deficiency  of  this  nerve  and 
the  parts  to  which  it  is  distributed,  in  ordinary  sensibility,  it  serves 
to  transmit  impressions  of  a  special  character,  which  are  connected 
with  two  different  but  associated  functions,  namely :  1.  The  sense  of 
taste,  and,  2.  The  act  of  deglutition. 

Connection  with  the  Sense  of  Taste. — The  sensation  of  taste  exists 
not  only  in  the  anterior  portion  of  the  tongue  supplied  from  the  lingual 
branch  of  the  fifth  pair,  but  also  at  the  base  of  the  organ,  throughout 
its  posterior  third,  and  in  the  arches  of  the  palate,  supplied  by  fibres 
of  the  glossopharyngeal.  But  while  the  region  supplied  by  the  fifth 
pair  possesses  also  a  tactile  sensibility  of  high  grade,  in  the  posterior 
region  the  general  sensibility  is  much  inferior  to  that  of  taste.  The 
method  adopted  by  Longet  for  examining  the  sense  of  taste  in  dogs 
was  to  place  on  the  base  of  the  tongue  a  few  drops  of  a  concentrated 
solution  of  colocynth.  Although  this  always  produced,  in  the  natural 
condition  of  the  animal,  manifest  signs  of  disgust,  it  had  no  such  effect, 
as  a  rule,  after  section  of  the  glossopharyugeal  nerves,  provided  the 
solution  were  applied  only  to  the  posterior  part  of  the  tongue  and  the 
pharynx;  while  if  even  a  minute  quantity  came  in  contact  with  tin- 
tip  or  edges  of  the  organ  it  caused  brisk  movements  of  the  jaws 
with  all  the  indications  of  repugnance.  In  the  anterior  and  more 
movable  parts  of  the  tongue,  accordingly,  the  sensations  of  taste  are 
appreciated,  during  mastication,  by  the  filaments  of  the  lingual  nerve. 
The  glossopharx  nireal,  on  the  other  hand,  is  the  nerve  of  taste  for  the 
posterior  part  of  the  organ;  and  is  called  into  activity  after  mastica- 
tion  is  accomplished,  when  the  food  is  carried  backward  for  deglutition 
and  compressed  by  the  base  of  the  tongue,  the  pillars  of  the  fauces, 
and  the  walls  of  the  pharynx. 


*  Todd's   Cyclopedia   of    Anatomy    and    Physiology.      Article, 

AVnr. 


THE    CRANIAL    NERVES.  481 

Connection  with  Deglutition.  —  In  the  fauces  and  pharynx,  the 
glossopharyngeal  nerve  is  sensitive  to  certain  impressions,  which 
excite  the  muscles  of  the  neighboring  parts  and  bring  into  play  the 
mechanism  of  deglutition.  The  beginning  of  this  process  consists  in 
drawing  backward  and  upward  the  base  of  the  tongue,  by  which  the 
masticated  food  is  carried  through  the  isthmus  of  the  fauces  into  the 
pharynx.  Next,  the  muscles  of  the  pillars  of  the  fauces  (palatoglossal 
and  palatopharyngeal)  close  the  opening  of  the  isthmus,  while  the  soft 
palate  is  extended  across  the  upper  end  of  the  pharynx,  shutting  off  its 
communication  with  the  posterior  nares ;  and  the  constrictor  muscles 
of  the  pharynx  then  force  its  contents  downward  into  the  oesophagus. 
This  is  an  involuntary  reflex  action.  The  contraction  of  the  muscles, 
and  their  coordination  in  a  series  of  successive  movements,  will  take 
place  even  in  a  state  of  unconsciousness  under  the  stimulus  of  food  or 
liquids  in  contact  with  the  fauces  and  pharynx.  This  contact  produces 
an  impression  which  is  conveyed  by  the  glossopharyngeal  nerve  inward 
to  the  medulla  oblongata,  whence  it  is  reflected  in  the  form  of  a  motor 
impulse. 

Motor  Properties  of  the  Glossopharyngeal. — Although  this  nerve 
appears  to  be  exclusively  sensitive  at  its  origin,  it  is  found,  when 
examined  outside  the  cranium,  to  possess  motor  properties.  In  the 
experiments  of  Mayo  on  the  ass,  confirmed  by  those  of  Longet  on 
the  horse  and  dog,  irritation  of  the  glossopharyngeal  nerve  in  the 
neck  produced  contraction  of  the  stylopharyngeal  muscle  and  the 
upper  part  of  the  pharynx.  These  movements  were  the  result  of 
direct  motor  action,  since,  in  the  experiments  of  Longet,  they  were 
excited  by  irritating  the  peripheral  extremity  of  the  divided  nerve. 

The  glossopharyngeal,  therefore,  after  its  exit  from  the  jugular  fora- 
men, is  a  mixed  nerve.  In  addition  to  its  original  sensitive  filaments, 
it  has  received  a  branch  of  communication  from  the  facial,  and  also 
a  branch  from  the  pneumogastric.  The  latter  branch  is  regarded,  on 
anatomical  grounds,  as  made  up,  wholly  or  in  part,  of  motor  fibres 
coming  from  the  spinal  accessory,  through  its  anastomosis  with  the 
pneumogastric.  The  results  obtained  by  experiment  also  indicate  a 
double  source  for  the  motor  fibres  of  the  glossopharyngeal  nerve.  If 
these  were  derived  exclusively  from  either  the  facial  or  the  spinal 
accessory,  the  division  of  one  or  the  other  of  these  nerves  above  its 
communicating  branch  would  abolish  completely  the  motor  power  of 
the  glossopharyngeal.  But  the  experiments  of  Bernard  and  Longet, 
in  which  the  facial  nerve  was  divided  in  the  aqueduct  of  Fallopius,  and 
those  in  which  the  spinal  accessory  was  destroyed  on  both  sides,  show 
that  the  process  of  deglutition,  though  retarded,  is  not  abolished  by 
either  operation. 

Beside  these  anastomotic  branches  near  its  origin,  the  glosso- 
pharyngeal is  joined  by  a  second  branch  from  the  facial,  which  accom- 
panies it  to  the  styloglossal  muscle,  and  perhaps  also  to  the  pillars  of 
the  fauces ;  and,  according  to  Cruveilhier,  a  branch  derived  from  the 

2F 


482  THE    NERVOUS    SYSTEM. 

spinal  accessory  takes  part  in  the  formation  of  the  pharyngeal  plexus 
supplying  the  upper  constrictor  muscles  of  the  pharynx.  The  process 
of  deglutition,  therefore,  is  excited  at  its  commencement  by  sensitive 
impressions  conveyed  through  the  glossopharyngeal  nerve ;  but  its 
movements  are  executed  by  a  reflex  impulse  transmitted  through  the 
motor  fibres  of  several  distinct  branches  of  communication. 

Tenth  Pair.    The  Pnenmogastric. 

The  pneumogastric  nerve,  remarkable  for  its  extensive  course  and 
varied  distribution,  has  received  its  name  from  the  two  most  important 
organs  in  which  it  terminates,  namely,  the  lungs  and  stomach.  It 
arises  from  the  side  of  the  medulla  oblongata  by  ten  or  fifteen  fila- 
ments, arranged  in  linear  series  continuously  with  those  of  the  glosso- 
pharyngeal. Their  nucleus  of  origin  is  an  extended  tract  of  gray  sub- 
stance on  the  posterior  surface  of  the  medulla  oblongata,  just  outside 
the  lower  extremity  of  the  fasciculus  teres.  This  deposit,  which,  by  the 
divergence  of  the  posterior  columns,  is  exposed  to  view  on  the  floor 
of  the  fourth  ventricle,  is  known  as  the  ala  cinerea.  At  its  anterior 
extremity  it  is  continuous  with  the  nucleus  of  the  glossopharyngeal ; 
and  at  its  posterior  extremity  it  joins  that  of  the  spinal  accessory. 
From  its  deep  surface  it  gives  out  the  root  fibres  of  the  pneumo- 
gastric nerve,  which  run  downward  and  outward  through  the  medulla, 
and  emerge,  in  the  above  mentioned  series  of  filaments,  from  its  lateral 
surface. 

The  filaments  of  the  pneumogastric,  after  leaving  the  medulla,  unite 
into  a  trunk  which  passes  out  of  the  cranium  by  the  jugular  foramen. 
Here  it  presents  a  ganglionic  swelling,  known  as  the  "jugular  ganglion." 
At  or  immediately  beyond  this  situation,  the  nerve  is  joined  by  a  motor 
branch  from  the  spinal  accessory  ;  and  it  afterward  receives  similar  fila- 
ments from  four  other  sources;  namely,  the  facial,  the  hypoglossal,  and 
the  anterior  branches  of  the  first  and  second  cervical  nerves. 

While  passing  down  the  neck  the  pneumogastric  nerve  contributes 
an  anastomotic  branch  to  the  pharyngeal  plexus.  Its  first  important 
branch  of  distribution  is  the  superior  laryngeal  nerve,  which  pene- 
trates the  larynx  by  an  opening  in  the  thyro-hyoid  membrane,  and  is 
distributed  to  the  mucous  membrane  of  the  epiglottis  and  the  larynirea] 
cavity.  It  also  gives  off  a  small  muscular  branch  to  the  inferior  con- 
st rictor  of  the  pharynx  and  to  the  crico-thyroid  muscle  of  the  larynx. 
It  supplies  several  filaments,  which,  with  others  from  the  great  sym- 
pathetic, form  the  laryngeal  plexus ;  and  by  this  plexus  it  sends  fibres 
to  the  upper  cardiac  nerves  of  the  sympathetic.  Other  filaments  which 
it  gives  off  in  the  neck  also  join  the  cardiac  branches  of  tin-  sympa- 
thetic, or  sometimes,  according  to  Cruveilhier,  pass  directly  to  the 
cardiac  plexus  beneath  the  arch  of  the  aorta. 

The  next  branch  is  the  inferior  laryngeal  nen-e,  which  separates 
from  tin-  imeunioirastric  after  its  entrance  into  the  chest,  and  ascends, 
between  the  trachea  and  u'sophatriis,  to  the  larynx,  giving  off  filaments 


THE    CRANIAL    NERVES. 


483 


FIG.  127. 


to  the  oesophagus  and  the  inferior  constrictor  of  the  pharynx.  This 
nerve  is  distributed  to  all  the  muscles  of  the  larynx,  except  the  crico- 
thyroid  already  supplied  by  the  su- 
perior laryngeal.  The  larynx  there- 
fore receives  from  the  pneumogastric 
two  different  branches,  of  distinct 
properties  and  functions.  The  supe- 
rior laryngeal  branch  is  mainly  a  sen- 
sitive nerve,  supplying  the  mucous 
membrane;  the  inferior  laryngeal 
branch  is  motor,  and  provides  for  the 
activity  of  the  laryngeal  muscles. 

The  most  important  dependency  of 
the  pneumogastric  nerve  in  the  chest 
is  the  pulmonary  plexus.  This  is 
formed  by  a  number  of  inosculating 
branches,  from  which  the  filaments 
of  distribution  pass,  along  the  bronchi 
and  their  subdivisions,  to  the  pulmo- 
nary lobules.  In  the  inferior  portion 
of  the  chest,  other  inosculating  branches 
surround  the  oesophagus  with  the 
cesophageal  plexus,  from  which  fibres 
are  supplied  to  its  mucous  membrane 
and  muscular  coat. 

The  pneumogastric  nerves,  after  re- 
union of  their  branches  below  the  pul- 
monary plexus,  enter  the  abdomen 
and  spread  out  in  two  sets  of  gastric 
branches,  wThich  supply  the  mucous 
membrane  and  muscular  coat  of  the 
stomach.  Those  from  the  left  pneu- 
mogastric nerve  supply  the  anterior 

wall  Of  the  organ,  and   send  filaments  ORIGIN  AND  CONNECTIONS  OF  THE  GLOSSO- 

tO   the   transverse  fissure  of  the  liver,  PHARYNGEAL,  PNEUMOGASTRIC,  AND  SPI- 

.    ,          i  •   i     ,1                                 .  NAL  ACCESSORY  NERVES.— l.Facial  nerve. 

into  Which  they  penetrate  1U  Company  2.  Glossopharyngeal.    3.  Pneumogastric. 

with  the  hepatic  plexus  of  the  sympa- 
thetic ;  those  from  the  right  pneumo- 
gastric supply  the  posterior  wall  of 
the  stomach,  and  finally  communicate 

With    the    SOlar    pleXUS    Of    the    SVmpa-      10-  TymPanic  plexus,  from  a  branch  of 


4.  Spinal  accessory.  5.  Hypoglossal.  6. 
External  (muscular)  branch  of  the  spinal 
accessory.  7.  Superior  laryngeal  branch 
of  the  pneumogastric.  8.  Pharyngeal 
plexus.  9.  Laryngeal  plexus  and  upper" 
cardiac  branches  of  the  pneumogastric. 


thetic. 


the  glossopharyngeal.    (Hirschfeld.) 


The  pneumogastric  nerve,  therefore,  is  distributed  to  the  passages 
by  which  air  and  food  are  introduced  into  the  body.  It  also  forms  con- 
nection at  several  points  with  the  great  sympathetic,  and,  through  it, 
sends  fibres  to  the  heart. 

Physiological  Properties  of  the  Pneumogastric. — According  to  Lon- 


484  THE    NERVOUS    SYSTEM. 

get,  the  pneumogastric  at  its  origin  is  exclusively  sensitive.  Irritation 
of  the  nerve  roots,  separated  from  the  medulla,  is  without  effect ;  but  if 
applied  to  the  trunk  of  the  nerve  at  a  lower  level,  it  excites  muscular 
contraction.  At  this  situation  the  nerve  contains  motor  fibres  derived 
from  the  spinal  accessory,  the  facial,  the  hypoglossal,  and  the  two  upper 
•  •ervieal  nerves.  It  is,  accordingly,  a  mixed  nerve,  and  is  capable  of 
providing  both  for  movement  and  sensibility  in  the  organs  to  which  it 
is  distributed. 

Its  sensibility,  however,  to  mechanical  irritation  is  but  slightly 
marked,  as  shown  by  the  experience  of  all  observers.  It  may  fre- 
quently be  divided,  in  the  unetherized  animal,  without  causing  signs 
of  pain  ;  and  tin's  want  of  reaction  is  at  times  so  complete  as  to  indi- 
cate entire  absence  of  ordinary  sensibility.  In  other  instances,  accord- 
ing to  Bernard,  it  appears  sensitive ;  but  the  conditions  on  which  this 
difference  depends  are  unknown.  It  is  certain  that,  as  a  rule,  the  pneu- 
mogastric  is  deficient  in  that  kind  of  sensibility  which  produces  pain ; 
and  the  organs  to  which  it  is  distributed  have  little  or  no  appreciation 
of  tactile  impressions.  Nevertheless,  it  evidently  possesses  a  sensibility 
of  peculiar  kind,  and  of  the  highest  importance  for  the  vital  functions. 

Connection  with  Respiration. — The  most  important  endowment  of 
the  pneumogastric  nerve  is  that  connected  with  the  movements  of  res- 
piration. Its  influence  in  this  respect  is  evident  from  the  results  fol- 
lowing its  division  in  the  neck. 

When  the  nerves  have  been  simultaneously  divided  on  both  sides  in 
the  dog,  and  the  slight  disturbance  which  immediately  follows  their  sec- 
tion has  subsided,  the  most  striking  change  produced  in  the  animal's 
condition  is  a  diminished  frequency  of  respiration.  The  respiratory 
movements  sometimes  fall  at  once  to  ten  or  fifteen  per  minute,  becom- 
ing, in  an  hour  or  two,  still  more  infrequent.  They  are  performed 
easily  and  regularly ;  and  the  animal,  if  undisturbed,  usually  remains 
quiescent,  without  any  special  sign  of  discomfort.  By  the  second  or 
third  day  the  respirations  are  often  reduced  to  five,  four,  or  even  three 
JKT  minute;  the  general  condition  of  the  animal  being  also  exceedingly 
sluggish.  The  movement  of  inspiration  is  slow,  easy,  and  silent,  occu- 
pying several  seconds  in  its  duration ;  while  that  of  expiration  is  sud- 
den and  audible,  and  is  accompanied  by  a  well-marked  effort,  which  has, 
to  some  extent,  a  convulsive  character.  The  intercostal  spaces  sink  in- 
ward during  the  lifting  of  the  ribs;  and  the  whole  movement  of  respi- 
ration has  an  appearance  of  insufficiency,  as  if  the  lungs  wrere  not  thor- 
oughly filled  with  air. 

Death  takes  place  from  one  to  six  days  after  the  operation  ;  the  only 
marked  symptoms  during  this  time  being  steady  failure  of  the  respira- 
tion, with  increasing  general  sluggishness.  After  death  the  lungs  are 
found  in  a  peeuli;ir  Mate  of  solidification  ;  of  a  dark  purple  color,  leath- 
ery ami  resisting  to  the  touch,  destitute  of  crepitation,  and  infiltrated 
with  lilood.  Pieces  of  the  pulmonary  tissue  cut  out  sink  in  water. 
The  plennil  >urface>.  however,  are  natural  in  appearance,  and  there  is 


THE    CRANIAL    NERVES.  485 

no  effusion  into  the  pleural  cavity.  The  lungs  are  simply  engorged 
with  blood,  and,  to  a  considerable  extent,  empty  of  air. 

The  inference  from  these  phenomena  is  that  the  pneumogastric  nerves 
are  the  channels  for  a  sensitive  impression  from  the  lungs  to  the  me- 
dulla oblongata  which  excites,  by  reflex  action,  the  movement  of  respira- 
tion. Consequently  when  they  are  divided,  their  impression  being  no 
longer  conveyed  to  the  nervous  centres,  the  reflex  act  in  the  medulla 
lacks  its  usual  stimulus,  and  the  movements  of  respiration  diminish  in 
frequency.  They  do  not  cease  altogether,  because  a  similar  impression 
comes  from  other  parts  of  the  circulatory  system.  But  the  lungs  are 
the  organs  most  directly  concerned  in  respiration,  and  the  most  sensi- 
tive to  its  deficiency ;  and  when  their  influence  is  cut  off,  the  greater 
part  of  the  normal  respiratory  stimulus  is  wanting.  The  medulla, 
accordingly,  reacts  less  frequently,  and  the  movements  of  respiration 
are  performed  at  longer  intervals. 

This  appears  to  be  the  only  explanation  which  will  account  for  the 
immediate  effects  of  dividing  the  pneumogastric  nerves.  The  infre- 
quency  of  respiration  which  follows  directly  upon  this  operation  is  not 
due  to  paralysis  of  the  respiratory  muscles.  It  is  not  accompanied  by 
dyspnoea,  nor  by  any  sign  of  distress  from  defective  respiration.  It  is 
evident  that  the  animal  does  not  feel  the  need  of  breathing  as  under 
ordinary  conditions,  and  consequently  makes  no  effort  to  compensate 
for  the  loss.  If  respiration  were  reduced  in  frequency,  the  pneumogas- 
tric nerves  remaining  entire,  a  sense  of  suffocation  would  soon  be  mani- 
fest. This  happens  when  the  breath  is  voluntarily  suspended;  the 
sensation  of  discomfort  being  first  perceptible  in  the  lungs,  but  after- 
ward extending  over  the  whole  system,  and  assuming  the  character 
of  an  intolerable  distress.  When  breathing  is  renewed,  the  unpleasant 
sensation  disappears,  as  inspiration  renovates  the  air  in  the  pulmonary 
cavities.  The  impression  transmitted  by  the  pneumogastric  nerves  to 
the  medulla  is  sufficient  to  maintain  respiration  at  its  normal  frequency. 
When  this  impression  is  cut  off,  the  rate  of  respiration  is  lowered  nearly 
one-half. 

But  the  subsequent  changes  after  this  operation  are  due  to  other 
causes.  When  the  pneumogastric  nerves  are  divided  in  the  middle  of 
the  neck,  the  fibres  of  the  inferior  laryngeal  nerve  are  involved  in  the 
section.  This  paralyzes  the  laryngeal  muscles,  including  those  which 
separate  the  vocal  chords  and  open  the  glottis  at  the  moment  of  inspi- 
ration (page  238).  The  glottis  is  then  left  in  a  condition  of  flaccidity, 
and  instead  of  opening  in  inspiration  for  the  admission  of  air,  it  col- 
lapses and  obstructs  the  passage.  The  quantity  of  air  entering  the 
lungs  is  thus  diminished,  and  the  aeration  of  the  blood  still  further 
impaired.  This  no  doubt  causes  the  general  sluggish  condition  of  the 
nervous  system  after  section  of  the  pneumogastrics.  The  medulla  par- 
ticipates in  this  derangement.  It  becomes  less  sensitive  to  the  respira- 
tory stimulus  ;  and  as  the  stimulus  itself  is  diminished,  these  conditions 
react  upon  each  other,  and  increase  the  difficulty  of  respiration.  Thus 


TIT  K   NKI:  v<>rs  SYSTEM. 

the  breathing  becomes  slower  and  slower,  until  it  is  at  last  so  infre- 
quent that  it  can  no  longer  sustain  life. 

Furthermore,  the  physical  change  in  the  pulmonary  tissues  is  super- 
added  to  their  functional  derangement.  This  alteration  has  no  inflam- 
matory character,  but  consists  in  a  diminution  of  the  air  in  the  vesicle- 
of  the  lungs,  and  a  passive  accumulation  of  blood  in  the  capillaries. 
It  combines  with  the  causes  already  described,  to  interfere  with  tl it- 
aeration  of  the  blood  and  to  hasten  the  failure  of  the  vital  powers. 

Protection  of  the  Glottis  from  Foreign  Substances. — The  superior 
laryngeal  branch  of  the  pneumogastric  supplies  to  the  mucous  mem- 
brane of  the  larynx  a  peculiar  sensibility  which  is  essential  for  the  pro- 
tection of  the  respiratory  passages.  It  stands  as  a  sort  of  sentinel,  at 
the  entrance  of  the  glottis,  to  prevent  the  intrusion  of  foreign  sub- 
stances. If  a  crumb  of  bread  fall  within  the  aryteno-epiglottidean 
folds,  or  on  the  edges  of  the  vocal  chords,  the  sensibility  of  the  parts 
excites  an  expulsive  cough,  by  which  the  foreign  body  is  dislodged. 
The  impression  conveyed  inward  by  the  superior  laryngeal  nerve  is 
reflected  upon  the  expiratory  muscles  of  the  chest  and  abdomen,  by 
which  the  movement  of  coughing  is  accomplished.  This  reaction  is 
dependent  on  the  sensibility  of  the  laryngeal  mucous  membrane ;  and 
it  can  no  longer  be  produced  after  section  of  the  superior  laryngeal 
nerve. 

Connection  with  the  Voice. — In  addition  to  its  function  in  respiration, 
the  larynx  is  an  organ  for  the  production  of  vocal  sounds.  The  forma- 
tion of  the  voice  can  be  studied  in  animals  after  exposing  the  glottis 
by  the  operation  of  pharyngotomy ;  and  in  man  by  the  use  of  the 
laryngoscope.  The  first  important  fact  demonstrated  in  this  way  is 
that  the  voice  is  formed  always  in  expiration,  never  in  inspiration.  The 
column  of  outgoing  air  is  set  in  vibration  by  the  glottis,  and  its  res- 
onance modified  in  the  pharynx,  mouth,  and  nasal  passages.  Secondly, 
it  requires  tension  and  approximation  of  the  vocal  chords,  by  which  the 
orifice  of  the  glottis  is  narrowed  to  a  comparatively  minute  crevice. 
When  the  vocal  chords  are  relaxed  during  expiration,  nothing  can  be 
heard  except  a  faint  whisper  of  the  air  passing  through  the  larynx. 
In  the  production  of  a  vocal  sound  the  chords  are  made  tense  and 
closely  applied  to  each  other ;  and  the  air,  driven  by  forcible  expiration 
through  the  narrowed  chink  of  the  glottis,  between  the  vibrating  vocal 
chords,  is  itself  thrown  into  sonorous  vibration.  The  tone,  pitch,  and 
intensity  of  the  sound  vary  with  the  conformation  of  the  larynx,  the 
tension  and  approximation  of  the  vocal  chords,  and  the  force  of  expira- 
tion. The  narrower  the  opening  and  the  greater  the  tension  of  the 
chords,  the  more  acute  the  sound;  while  a  wider  opiMiin.tr  and  a  lower 
t< •  n -ion  produce  a  graver  note.  The  quality  of  the  sound  is  also  modi- 
fied by  the  length  of  the  column  of  air  between  the  glottis  and  the 
mouth,  the  tense  or  relaxed  condition  of  the  pharynx  and  fauces,  and 
the  dryness  or  moist  urn  of  the  mucous  membrane. 

The  production  of  a  vocal  sound  takes  place,  therefore,  in  the  larvnx  j 


THE    CRANIAL    NERVES.  487 

while  articulation,  or  division  of  the  sound  into  vowels  and  consonants, 
words  and  phrases,  is  accomplished  by  the  lips,  tongue,  teeth,  and  pal- 
ate. Consequently,  division  of  the  pneumogastric  nerve  or  of  its  inferior 
laryngcal  branch  on  both  sides,  produces  loss  of  voice.  Furthermore, 
as  vocalization  and  articulation  are  distinct  nervous  actions,  they  may 
be  deranged  independently  of  each  other,  by  injury  or  disease  of  different 
parts  of  the  nervous  system.  The  movements  of  articulation  are  regu- 
lated by  the  facial  and  hypoglossal  nerves ;  while  vocalization  is  under 
the  control  of  the  pneumogastric. 

Connection  with  Deglutition. — The  act  of  deglutition,  which  com- 
mences in  the  fauces  and  pharynx,  is  continued  and  completed  by  the 
lower  portion  of  the  pharynx  and  by  the  oesophagus.  These  parts 
receive  both  their  sensitive  and  motor  filaments  from  the  pneumogastric 
nerve,  and  under  its  influence  'the  food,  once  started  on  its  downward 
passage,  is  conducted  by  the  peristaltic  action  of  the  oesophagus  into 
the  stomach. 

The  inferior  constrictor  of  the  pharynx  and  the  cervical  portion  of 
the  oesophagus  both  receive  filaments  from  the  inferior  laryngeal  nerve  ; 
while  the  thoracic  portion  of  the  oesophagus  is  supplied  from  the  trunk 
of  the  pneumogastric.  Deglutition,  therefore,  becomes  incomplete,  as 
shown  by  Bernard  in  dogs,  horses,  and  rabbits,  by  division  of  the 
pneumogastric  nerves  in  the  neck.  The  masticated  food  is  still  con- 
veyed by  the  pharynx  from  the  fauces  to  the  oesophagus ;  but  here  it 
accumulates,  distending  the  walls  of  the  paralyzed  canal,  and  finding 
its  way  into  the  stomach  only  in  small  quantities  under  the  pressure 
from  above.  The  normal  process  of  swallowing  is  accomplished  by 
a  series  of  contractions,  beginning  at  the  fauces  and  ending  at  the 
stomach.  Each  portion  of  the  mucous  membrane  receives  in  turn  a 
stimulus  from  the  contact  of  the  food,  followed  by  excitement  of  the 
corresponding  muscle ;  so  that  the  alimentary  mass  is  carried  rapidly 
downward  by  reflex  action,  independent  of  voluntary  control.  Section 
of  the  pneumogastric  nerves  destroys  sensibility  and  motive  power 
in  the  oesophagus,  and  consequently  interferes  with  deglutition. 

Protection  of  the  Glottis  in  Deglutition. — As  the  laryngeal  orifice 
communicates  directly  with  the  cavity  of  the  pharynx,  and  as  all  solids 
and  liquids,  in  swallowing,  pass  over  its  surface,  portions  of  the  food 
would  find  their  way  into  the  larynx  unless  there  were  some  means  for 
its  protection.  The  epiglottis,  which  stands  in  front  of  the  glottis,  and 
shuts  over  it  like  a  cover  when  the  tongue  is  drawn  back  in  degluti- 
tion, might  seem  to  be  a  safeguard  in  this  respect. 

But  experience  shows  that  this  organ  is  not  essential  to  protect  the 
glottis  in  deglutition.  It  may  be  completely  excised,  in  dogs,  without 
any  subsequent  difficulty  in  swallowing  either  liquid  or  solid  food. 
The  epiglottis,  furthermore,  exists  only  in  mammalians,  being  absent 
in  all  other  vertebrate  animals.  Finally,  the  epiglottis  does  not  pre- 
vent foreign  substances  passing  into  the  larynx  when  the  other  con- 
ditions of  normal  deglutition  are  disturbed.  The  protection  of  the 


488  T  n  K  N  E  it  v  o  r  s  SYSTEM. 

glottis  against  the  entrance  of  food  does  not  depend  on  a  mechani- 
cal obstacle,  but  on  a  special  association  of  nervous  acts. 

The  first  requisite  for  swallowing  is  the  suspension  of  respiration. 
This  takes  place,  at  the  beginning  of  deglutition,  by  an  influence  desig- 
nated as  tin-  "  action  of  arrest."  The  same  nervous  impression  which 
excites  contraction  of  the  pharynx,  suspends  for  a  time  the  movement 
of  inspiration. 

The  effect  of  this  arrest  is  to  prevent  the  opening  of  the  glottis. 
As  the  respiratory  movements  of  the  glottis  are  coincident  with  those 
of  the  chest,  and  are  excited  by  the  same  nervous  influence,  the  impres- 
sion which  puts  a  stop  to  one  also  suspends  the  other.  The  glottis 
consequently  not  being  opened  when  food  enters  the  pharynx,  its 
liability  to  admit  any  portion  of  the  alimentary  mass  is  considerably 
diminished.  But  it  is  furthermore  completely  closed  by  the  inferior 
constrictor  of  the  pharynx,  the  most  active  muscle  in  the  apparatus  of 
deglutition;  since  the  fibres  of  this  muscle  are  attached  to  the  exter- 
nal surface  and  borders  of  the  thyroid  cartilage,  thus  compressing  the 
larynx  on  both  sides  at  the  instant  of  deglutition.  By  this  means  the 
glottis  is  protected,  as  in  birds  and  reptiles,  even  where  an  epiglottis  is 
wanting. 

The  accident  by  which  food  or  foreign  substances  sometimes  gain 
access  to  the  larynx,  in  man,  is  always  caused  by  a  sudden  attempt  at 
inspiration.  This  cannot  take  place  during  deglutition  in  the  ordinary 
state  of  the  nervous  system;  but  it  may  be  produced  by  any  unex- 
pected shock  or  excitement  which  disturbs  the  coordination  of  the 
reflex  actions.  Such  a  shock  usually  causes,  as  its  first  effect,  a  spas- 
modic inspiration ;  and  if  this  take  place  while  food  is  passing  through 
the  pharynx,  a  portion  of  it  finds  its  way  through  the  open  orifice  of 
the  glottis  into  the  larynx. 

Connection  with  Stomach  Digestion. — The  effect  produced  on  the 
stomach  by  division  of  the  pneumogastric  nerve  shows  that  its  influ- 
ence on  this  organ  is  mainly  similar  to  that  which  it  exerts  on  the 
oasophagus ;  that  is,  it  supplies  the  mucous  membrane  with  a  special 
sensibility  to  the  contact  of  food,  and  provides  for  the  peristaltic  action 
of  the  muscular  coat.  After  section  of  both  pneumogastric  nerves  in 
the  neck,  the  sensations  of  hunger  and  thirst  remain;  the  animals 
often  exhibiting  a  desire  for  food  and  drink,  which  they  sometimes  take 
in  considerable  quantity,  though  but  little  reaches  the  stomach,  owing 
to  the  paralysis  of  the  esophagus.  In  the  experiments  of  Bernard  on 
dogs,  the  secretion  of  gastric  juice  was  suspended  after  this  operation, 
and  food  introduced  into  the  stomach  through  a  gastric  fistula  remained 
undigested.  But  Longet  found  that  if  the  food  were  introduced  only 
in  small  quantity,  it  might  cause  the  secretion  of  gastric  juice,  and  lie 
finally  digested.  This  indicates  that  secretion  and  digestion  in  the 
stomach  are  not  immediately  under  the  control  of  the  pneumoirnstric 
nerve,  but  that  after  its  section  they  become  practically  suspended, 
owing  mainly  to  paralysis  of  the  muscular  coat. 


THE    (5 II  AX  1  AT,    NERVES.  489 

According  to  Bernard,  the  finger,  if  introduced  into  the  stomach 
through  a  gastric  fistula  in  a  healthy  dog,  is  compressed  with  considera- 
ble force  by  the  walls  of  the  organ ;  but  this  pressure  disappears  com- 
pletely on  division  of  the  pneumogastric  nerves.  The  absence  of  mus- 
cular action  in  a  paralyzed  stomach  is  sufficient  to  account  for  the  failure 
of  digestion.  This  action  is  necessary  to  bring  successive  portions  of  the 
food  in  contact  with  the  mucous  membrane,  and  for  the  thorough  admix- 
ture of  gastric  juice  with  the  alimentary  mass.  The  pneumogastric 
nerves  therefore  supply  to  the  stomach  a  sensibility  and  motor  power, 
which  are  practically  essential  to  the  digestive  process. 

Influence  on  the  Heart. — The  pneumogastric  filaments,  destined  for 
distribution  in  the  heart,  are  partly  derived  from  its  superior  laryngeal 
branch,  whence  they  join  the  upper  cardiac  nerve  coming  from  the 
superior  cervical  ganglion  of  the  sympathetic.  Others  are  furnished 
by  the  trunk  of  the  pneumogastric  in  the  neck,  which  inosculates  with 
the  continuation  of  the  upper  cardiac  nerve.  The  inferior  laryngeal 
branch,  during  its  reascending  course,  supplies  so  many  filaments  to  the 
same  plexus  that,  according  to  Cruveilhier,  it  sometimes  appears  dis- 
tributed in  almost  equal  proportions  to  the  larynx  and  to  the  heart. 
Finally  other  small  branches  of  the  pneumogastric  in  the  chest  lose 
themselves  at  once  in  the  cardiac  plexus,  beneath  the  arch  of  the  aorta. 
All  the  filaments,  accordingly,  finally  reaching  the  heart  through  the 
cardiac  plexus,  originate  either  from  the  sympathetic  or  the  pneumo. 
gastric ;  and  the  entire  group  is  characterized  by  the  frequent  and  inti- 
mate admixture  of  fibres  from  these  two  sources. 

The  effect  produced  on  the  heart  by  irritation  of  the  pneumogastric 
is  precisely  the  opposite  to  that  usually  caused  by  irritating  the  nerves 
of  a  muscular  organ.  If  the  heart  be  exposed  in  a  warm-blooded  quad- 
ruped by  opening  the  chest,  and  the  circulation  maintained  by  artificial 
respiration,  the  action  of  the  pneumogastric  may  be  studied  by  apply- 
ing to  its  trunk  the  poles  of  a  galvano-faradic  apparatus.  On  stimu- 
lating the  nerve  in  this  way  with  an  interrupted  current  of  moderate 
strength,  the  first  visible  effect  is  a  diminution  in  frequency  of  the  car- 
diac pulsations.  If  the  intensity  of  the  current  be  increased,  the  heart 
acts  still  more  slowly;  and  with  a  further  increase  of  intensity  it  stops 
altogether. 

When  the  faradization  of  the  nerve  is  suspended,  the  cardiac  pulsa- 
tions recommence  ;  and  this  may  be  repeated  for  many  successive  trials. 

There  are  three  important  facts  to  be  noted  in  regard  to  these  phe- 
nomena : 

I.  When  the  heart  ceases  to  move,  under  the  faradization  of  the 
nerve,  it  stops  in  the  condition  of  muscular  relaxation.  It  lies  flaccid 
and  motionless,  while  its  cavities  are  slowly  filled  with  blood  returning 
from  the  venous  system.  On  stopping  the  faradization,  on  the  other 
hand,  the  first  sign  of  activity  in  the  heart  is  a  normal  pulsation. 
Stimulation  of  the  pneumogastric  nerve,  accordingly,  tends  to  arrest 
the  muscular  action  of  the  heart. 


490  THE     NF.RYors    SYSTEM. 

II.  If  the  pnmmo.irastric  nerve  be  divided,  and  the  faradic  current 
applied  to  its  central  extremity,  the  heart's  pulsations  are  not  inter- 
rupted ;  but  when  the  current  is  applied  to  the  peripheral  extremity  of 
the  nerve,  they  cease  as  before.     The  influence  therefore  which  arrests 
the  heart's  action,  under  stimulation  of  the  pneumogastric,  is  not  a 
centripetal  influence,  operating  through  the  nervous  centres  ;  it  is  a 
centrifugal  influence,  passing  from  above  downward  through  the  pneu- 
mogastric to  the  heart. 

III.  After  stimulating  the  pneumogastric  nerve  with  a  current  suffi- 
cient to  stop  the  cardiac  pulsations,  if  the  current  be  continued  the  heart 
does  not  remain  motionless.     At  the  end  of  ten  or  fifteen  seconds  it 
performs  a  beat.     A  little  later  this  is  repeated,  and  the  pulsations  then 
recur,  with  increasing  frequency,  until  their  normal  rate  is  reestab- 
lished, notwithstanding  the  continued  faradization  of  the  nerve.     This 
shows  that  the  nervous  action  which  arrests  the  heart  is  exhausted 
after  a  certain  time.     If  the  stimulation  be  now  applied  to  the  pneu- 
mogastric nerve  of  the  opposite  side,  the  heart  stops,  as  before.     The 
heart,  accordingly,  is  still  sensitive  to  the  action  of  arrest ;  it  is  the 
nerve  only  which,  by  continued  excitement,  loses  the  power  of  exerting 
this  action.    But  after  a  pneumogastric  nerve  has  been  thus  exhausted, 
so  that  it  no  longer  retards  the  cardiac  pulsations,  if  allowed  to  repose 
for  a  time,  and  again  stimulated,  it  again  stops  the  heart ;  showing 
that  it  has  recovered  the. power  which  it  had  temporarily  lost.      In 
these  respects,  the  influence  of  the  pneumogastric  nerve  on  the  heart 
resembles  that  of  a  motor  nerve  on  the  muscles  of  the  limbs.     The 
difference  between  the  two  is  in  their  effect.    An  ordinary  motor  nerve, 
when  stimulated,  causes  contraction  of  the  corresponding  muscle ;  stimu- 
lation of  the  pneumogastric  nerve,  as  connected  with  the  heart,  causes 
relaxation. 

Eleventh  Pair.    The  Spinal  Accessory. 

This  nerve,  so  named  from  its  spinal  origin  and  subsequent  associa- 
tion with  the  cranial  nerves,  consists  of  filaments  emerging  from  the 
cervical  portion  or  the  spinal  cord,  from  the  level  of  the  fourth  or 
fifth  cervical  nerve  upward  (Fig.  127, 4).  They  unite  into  a  slender 
cord,  which  ascends  between  the  anterior  and  posterior  roots  of  the 
cervical  spinal  nerves,  to  the  foramen  magnum,  where  it  enters  the 
cranial  cavity.  Here  it  receives  a  new  supply  of  root  fibres  from  the 
medulla  oblongata,  arranged  in  a  continuous  line  with  those  of  the 
pneumogastric.  The  nerve  trunk,  thus  constituted  by  the  union  of  its 
spinal  and  medullary  roots,  accompanies  the  pneumogastric  and  glos- 
sopharyngeal  nerves  in  their  passage  through  the  jugular  foramen. 

The  central  origin  of  this  nerve  is  a  collection  of  nerve  cells  situated 
in  the  upper  portion  of  the  spinal  cord  and  the  medulla  oblongata, 
on  the  outer  and  posterior  aspect  of  the  anterior  horn  of  gray  sub- 
stance. From  this  source  its  fibres  curve  downward  and  outward  to 
their  point  of  emergence  on  the  lateral  surface  of  the  medulla. 


THE    CRANIAL    NERVES.  491 

While  passing  through  the  jugular  foramen,  the  spinal  accessory 
becomes  adherent  to  the  jugular  ganglion  of  the  pneumogastric,  but 
without  taking  part  in  its  formation,  except  by  furnishing  one  or  two 
small  filaments  of  communication.  Immediately  after  its  exit  from  the 
foramen  it  divides  into  two  main  branches ;  namely,  1st,  the  internal, 
or  anastomotic  branch,  which  joins  the  trunk  of  the  pneumogastric, 
and  2dly,  the  external,  or  muscular  branch,  which  passes  downward 
and  outward  and  is  distributed  to  the  sterno-mastoid  and  trapezius 
muscles.  According  to  many  observers  (Bernard,  Cruveilhier,  Henle, 
Longet)  the  internal  or  anastomotic  branch  is  made  up  of  fibres  from 
the  medulla  oblongata;  the  external  or  muscular  branch  consists  of 
those  originating  from  the  spinal  cord. 

The  spinal  accessory  is  without  question  a  motor  nerve.  According 
to  Bernard  and  Longet,  mechanical  or  galvanic  irritation  applied,  within 
the  cranium,  to  the  central  extremity  of  the  divided  nerve,  causes  no 
indication  of  sensibility.  On  the  other  hand  its  fibres  may  be  traced 
in  great  part  directly  to  their  termination  in  muscular  tissues,  and  its 
division  or  evulsion  induces  effects  which  consist  exclusively  in  the  loss 
of  motive  power. 

The  most  complete  method  of  experimenting  on  this  nerve  is  that 
adopted  by  Bernard,  namely,  its  evulsion.  For  this  purpose,  the  mus- 
cular branch  of  the  nerve  is  followed  by  dissection  to  its  point  of 
emergence  from  the  jugular  canal,  where  it  separates  from  the  anas- 
tomotic branch.  The  combined  trunk  is  then  seized  between  the 
blades  of  a  forceps,  and  by  steady  and  continuous  traction  the  whole 
nerve,  with  its  medullary  and  spinal  roots,  may  be  extracted  entire.  By 
appropriate  variations  of  the  procedure,  either  the  medullary  portion 
with  the  anastomatic  branch,  or  the  cervical  portion  with  the  external 
branch,  may  be  removed  separately,  and  the  comparative  effects  of  the 
two  operations  observed.  But  when  the  whole  trunk  is  extracted  as 
above,  all  its  fibres,  both  anastomotic  and  muscular,  are  destroyed  at 
the  same  time. 

The  most  striking  effects  of  this  operation  are  those  due  to  paralysis 
of  the  internal  or  anastomotic  branch.  From  this  branch  the  pneu- 
mogastric nerve  receives  a  large  share  of  its  motor  fibres.  According 
to  Cruveilhier,  the  pharyngeal  filament  is  sometimes  given  off  exclu- 
sively from  the  anastomotic  branch  of  the  spinal  accessory,  sometimes 
partly  from  this  branch  and  partly  from  the  pneumogastric.  Beyond 
this  point,  the  fibres  of  the  pneumogastric  nerve  derived  from  the  spinal 
accessory  can  no  longer  be  followed  by  dissection  ;  but  the  results  of 
experiment  show  that  they  are  finally  distributed,  through  the  inferior 
laryngeal  branch,  to  the  muscles  of  the  larynx,  where  they  preside  over 
its  action  as  a  vocal  organ. 

After  evulsion  of  the  spinal  accessory  nerve  on  both  sides,  the  most 
noticeable  result  is  loss  of  power  to  produce  vocal  sounds.  The  respi- 
ratory movements  of  the  glottis  are  not  interfered  with  ;  but  the  voice 
is  completely  lost,  as  much  so  as  if  the  inferior  laryngeal  nerves,  or 


THE    NERVOUS    SYSTEM. 

the  pneamogastric  trunks  themselves,  had  been  divided.  The  total 
result  in  the  two  cases,  however,  is  very  different.  Section  of  the 
pneumogastrics,  or  of  their  inferior  laryngeal  branches,  paralyzes  all 
the  movements  of  the  glottis,  those  of  respiration  as  well  as  those  of 
phonation;  since  tliese  nerves  contain  all  the  motor  fibres  distributed 
t«.  the  larynx,  exn-pt  those  for  the  crico-thyroid  muscles.  On  the  other 
hand,  evulsion  of  the  spinal  accessory  nerves  paralyzes  the  movements 
of  ph< mat  ion  alone,  namely,  those  in  which  the  vocal  chords  are  approxi- 
mated and  the  rima  glottidis  narrowed;  leaving  untouched  the  move- 
ments of  respiration,  in  which  the  vocal  chords  are  separated  and  the 
glottis  opened. 

The  larynx,  accordingly,  performs  two  distinct  functions,  and  is  sup- 
plied with  motor  nerves  from  two  different  sources.  Those  which 
preside  over  the  production  of  sound  originate  from  the  spinal  acces- 
sory ;  those  for  respiration  are  derived  from  other  motor  nerves  (facial, 
hypoglossal,  cervical)  which  also  communicate  with  the  pneumogastrics. 

The  function  of  the  external  or  muscular  branch  of  the  spinal  acces- 
sory nerve  is  not  so  fully  understood.  The  sternomastoid  and  tra- 
pezius  muscles,  to  which  it  is  distributed,  also  receive  filaments  from 
the  cervical  spinal  nerves ;  and  they  still  retain  the  power  of  motion 
after  evulsion  of  the  spinal  accessory  on  both  sides.  The  sterno- 
mastoid and  trapezius  muscles  have  no  such  peculiar  action  as  that 
of  the  larynx  in  vocalization ;  and  it  is  not  easy  to  distinguish  what 
movements  of  these  muscles  are  paralyzed  by  division  of  the  spinal 
accessory,  and  what  remain  unaffected.  The  most  plausible  conclusions 
are  those  derived  by  Bernard  from  the  continued  observation  of  animals 
after  division  of  these  nerves. 

According  to  this  view,  the  external  branch  of  the  spinal  accessory, 
like  the  internal  branch,  performs  a  function  antagonistic  to  respiration. 
Respiration  is  naturally  suspended  during  strenuous  and  prolonged 
muscular  effort.  In  the  acts  of  straining,  lifting,  pushing,  and  the 
like,  respiration  ceases,  the  spinal  column  is  made  rigid,  and  the  head 
and  neck  are  fixed  in  position  largely  by  means  of  the  sternomastoid 
and  trapezius  muscles.  Such  efforts  cannot  be  made  with  success  if 
these  muscles  be  paralyzed.  According  to  Bernard,  they  also  take  part 
in  the  production  of  a  cry,  or  prolonged  vocal  sound.  After  destruc- 
tion of  the  entire  spinal  accessory  the  voice  is  completely  abolished  by 
paralysis  of  the  laryn«rcal  muscles.  If  its  external  branch  alone  be 
divided,  the  animal  can  still  produce  a  vocal  sound;  but  this  sound 
cannot  be  prolonged  into  a  cry,  and  the  voice  is  confined  in  duration 
to  the  ordinary  length  of  an  expiratory  movement.  Although  the 
animals,  furthermore,  are  apparently  not  otherwise  inconvenienced  by 
this  operation  so  lon<_r  as  they  remain  quiet,  any  increased  exertion,  as 
in  runninir  or  leaping.  «-aii>es  a  want  of  harmony  between  respiration 
and  muscular  action,  which  results  in  shortness  of  breath. 

The  Mernoinastoid  and  trape/ius  muscles,  like  those  of  the  larynx, 
are  therefore  animated  by  two  sets  of  motor  fibres.  Those  coming 


THE    CRANIAL    NERVES.  493 

from  the  cervical  spinal  nerves  provide  for  the  ordinary  movements  of 
locomotion ;  those  derived  from  the  spinal  accessory  supply  the  stimu- 
lus for  continuous  muscular  exertion,  or  for  a  prolonged  vocal  sound. 

Twelfth  Pair.    The  Hypoglossal. 

The  hypoglossal  nerve,  or  the  motor  nerve  of  the  tongue,  emerges 
from  the  anterior  part  of  the  medulla  oblongata  by  ten  or  twelve 
slender  filaments  between  the  anterior  pyramids  and  the  olivary  bodies 
(Fig.  127,  5),  on  a  line  with  the  anterior  roots  of  the  cervical  spinal 
nerves. 

The  central  origin  of  these  fibres,  according  to  Clarke,  Dean,  Kolliker, 
Henle,  and  Meynert,  is  a  nucleus  of  gray  substance  in  the  posterior 
part  of  the  medulla  oblongata  next  the  median  line,  at  the  inferior  ex- 
tremity of  the  fourth  ventricle.  It  has  an  elongated  form,  extending 
from  the  divergence  of  the  posterior  columns  upward  and  forward  to 
the  level  of  the  auditory  nucleus.  It  is  parallel  in  position  with  the 
spinal  accessory  and  pneumogastric  nuclei,  but  situated  between  them 
and  the  median  line. 

During  the  passage  of  the  hypoglossal  nerve  roots  through  the 
medulla  oblongata,  they  reach  the  inner  surface  of  the  olivary  nucleus, 
and  pass  in  great  measure  between  the  folds  or  through  the  substance 
of  its  convoluted  wall.  It  is  shown  by  Dean*  that  although  a  direct 
continuity  between  the  root  fibres  of  the  nerve  and  the  cells  of  the 
olivary  nucleus  cannot  be  demonstrated,  yet  prolongations  of  these 
cells  can  sometimes  be  traced  upward  and  inward,  in  company  with 
the  nerve  roots,  toward  the  hypoglossal  nucleus ;  and  in  the  sheep, 
the  tracts  of  fibres  connecting  the  two  nuclei  are  very  evident.  Accord- 
ing to  Henle,  in  some  transverse  sections  through  the  olivary  body 
fibres  from  the  hypoglossal  nerve  roots  may  be  seen  bending  round 
the  inner  border  of  the  nucleus  into  its  interior  ;  while  others  emerge 
in  a  corresponding  manner  from  the  opposite  border  and  continue  on- 
ward, with  the  main  root-bundles,  to  the  hypoglossal  nucleus.  Although 
the  minute  anatomical  structure  of  these  parts  is  not  fully  made  out,  it 
is  evident  that  a  close  relation  exists  between  the  gray  substance  of 
the  olivary  bodies  and  the  hypoglossal  nucleus  and  roots. 

Kolliker  regards  the  roots  of  the  hypoglossal  nerves  as  undergoing 
complete  decussation  through  the  raphe,  at  the  level  of  the  nuclei. 
According  to  Clarke  and  Dean,  a  portion  of  the  fibres  of  each  root  ter- 
minate in  the  corresponding  nucleus,  while  another  portion  decussate 
with  those  of  the  opposite  side.  It  is  certain  that  the  hypoglossal,  like 
other  cranial  nerves,  has,  in  some  way,  a  connection  with  the  opposite 
side  of  the  brain ;  since  cases  of  facial  paralysis  from  cerebral  hemor- 
rhage are  often  accompanied  by  paralysis  of  the  tongue  on  the  same 
side  with  that  of  the  face,  and  opposite  to  the  lesion.  One  of  the  genio- 


*  Gray  Substance  of  the  Medulla  Oblongata  and  Trapezium.     Washington,  1864, 
p.  36. 


4:94  THE    NERVOUS    SYSTEM. 

hyoglossal  muscles  having  lost  its  power,  while  the  other  remains 
active,  the  point  of  the  tongue,  when  protruded,  deviates  toward  the 
paralyzed  side. 

After  leaving  tin-  medulla  oblongata,  the  fibres  of  the  hypoglossal 
nerve  become  parallel  with  each  other,  and,  passing  through  the  ante- 
rior condyloid  foramen,  emerge  from  the  skull  in  the  form  of  a  cylin- 
drical cord.  Immediately  beyond  this  point  it  presents  one  or  two 
branches  of  communication  with  th«  pneumogastric,  where  it  crosses 
the  track  of  this  nerve.  According  to  Cruveilhier,  these  branches  con- 
sist of  fibres  from  the  hypoglossal  nerve  which  join  those  of  the  pneu- 
mogastric,  and  run  with  them  in  a  peripheral  direction.  The  hypo- 
glossal  nerve  then  passes  downward,  nearly  to  the  level  of  the  hyoid 
bone,  where  it  curves  forward,  giving  filaments  to  the  styloglossal  and 
hyoglossal  muscles,  and  to  those  immediately  beneath  the  hyoid  bone ; 
after  which  it  turns  upward,  penetrating  the  tongue  from  below,  inos- 
culates with  the  lingual  branch  of  the  fifth  pair,  and  is  finally  distributed 
to  the  muscles  of  the  tongue.  It,  therefore,  animates  not  only  the  lin- 
gual muscles  proper,  but  also  those  which  draw  the  tongue  backward 
and  upward  (styloglossal),  and  backward  and  downward  (hyoglossal 
and  infrahyoid  muscles).  It  also  receives  filaments  from  the  first  and 
second  cervical  nerves,  which,  according  to  Cruveilhier,  are  fibres  of 
reinforcement,  accompanying  the  hypoglossal  nerve  to  its  peripheral 
termination. 

Physiological  Properties  of  the  Hypoglossal  Nerve. — The  motor 
character  of  this  nerve  is  easily  established  by  the  results  of  its  irrita- 
tion and  division.  If  it  be  exposed,  either  in  the  living  or  the  recently- 
killed  animal,  where  it  runs  parallel  to  and  a  little  above  the  hyoid 
bone,  its  irritation  produces  immediate  convulsive  action  of  the  tongue. 
The  same  effect  follows  irritation  applied  to  the  peripheral  extremity 
of  the  divided  nerve  ;  showing  that  the  contractions  thus  produced  are 
not  reflex,  but  due  to  a  direct  stimulus  conveyed  through  the  nerve  to 
the  tongue.  Whether  the  nerve  possess  also  sensitive  fibres  of  its 
own  is  not  certain.  Longet  obtained  in  this  respect  only  negative 
results;  the  division  of  the  nerve  roots  in  dogs,  between  the  occiput 
and  the  atlas,  not  producing  perceptible  signs  of  pain.  Outside  the 
cranial  cavity,  according  to  nearly  all  experimenters,  it  possesses  some 
de-Tee  of  sensibility;  but  this  is  probably  derived,  by  inosculation, 
from  the  first  and  second  cervical  nerves  near  the  base  of  the  skull,  and 
from  branches  of  the  fifth  pair  near  its  terminal  distribution.  Whatever 
sensibility  it  may  possess  is  destined  only  for  the  muscular  substance 
of  the  ton-lie,  and  not  for  its  mucous  membrane;  since  division  of  the 
linirnal  branch  of  the  fifth  pair  and  of  the  glossopharyn.u'eal  nerve 
destroys  sensibility  over  tin-  whole  surface  of  the  organ,  though  the 
hypoglossal  be  untouched;  and  secondly,  the  tongue  evinces  its  ordi- 
nary sensibility,  according  to  Longet,  after  the  division  of  both  hypo- 
nerve.-. 

Tin-  uniform  result  of  section  of  both  hypoglossal  nerves  is  loss 


THE    CRANIAL    NERVES.  495 

of  muscular  power  in  the  tongue,  while  its  tactile  and  gustatory  sen- 
sibilities are  preserved.  In  the  experiments  of  Panizza  and  Longet, 
the  animals  after  this  operation  were  unable  to  move  the  tongue  in 
any  direction ;  and  in  mastication  it  was  liable  to  be  caught  and 
wounded  by  the  teeth.  It  was  therefore  reduced  to  a  helpless  condi- 
tion, by  division  of  its  motor  nerves. 

Connection  with  Mastication  and  Deglutition. — Although  the  move- 
ments of  the  tongue  take  no  direct  part  in  mastication,  they  are  yet 
essential  to  its  performance,  by  bringing  successive  portions  of  the  food 
between  the  teeth  and  removing  those  which  have  undergone  tritura- 
tion.  In  animals  which  introduce  liquids  into  the  mouth  by  lapping, 
this  act  also  becomes  impossible  after  section  of  the  hypoglossal  nerves. 
The  action  of  the  lingual  muscles  is  practically  of  so  much  importance 
that,  according  to  Longet,  it  requires  great  expenditure  of  time  and 
patience,  in  keeping  animals  with  paralysis  of  the  tongue,  to  supply 
them  with  sufficient  nourishment  for  the  support  of  life. 

Connection  with  Articulation. — In  man,  another  function  performed 
by  the  tongue  is  that  of  articulation.  As  the  lingual  muscles  are  im- 
portant for  the  pronunciation  of  all  consonants  except  the  labials  (6, 
ra,  p)  and  the  labio-dentals  (/,  v),  as  well  as  for  that  of  the  vowels,  a, 
e,  i,  and  y,  their  paralysis  produces  a  nearly  complete  incapacity  of 
articulation.  In  man,  disease  or  injury  of  the  hypoglossal  nerve  alone 
is  a  rare  occurrence,  and,  when  it  exists,  is  almost  invariably  confined 
to  one  side.  In  glosso-labio-laryngeal  paralysis,  from  lesion  of  the 
medulla  oblongata  (p.  445),  the  disease  is  of  central  origin,  and  affects 
other  muscles  as  well  as  those  of  the  tongue.  In  these  cases,  however, 
the  imperfect  action  of  the  lingual  muscles  is  an  early  sign ;  and  when 
the  disease  is  fully  developed  and  the  tongue  completely  paralyzed,  all 
power  of  articulation  is  lost. 

The  hypoglossal  nerve,  accordingly,  though  one  of  the  simplest  of 
the  cranial  nerves  in  its  physiological  endowments,  is  important  as  an 
aid  in  mastication  and  deglutition,  and  essential  for  the  production  of 
articulate  speech. 


CHAPTER  VII. 
THE   SYMPATHETIC   SYSTEM. 

THE  sympathetic  nerves,  as  compared  with  those  of  the  cerebro- 
spinal  system,  have  certain  peculiarities  of  arrangement  and  dis- 
tribution. The  double  nervous  cord  running  through  the  great  cavi- 
ties of  the  body,  the  numerous  and  scattered  ganglia,  united  with 
each  other  by  slender  filaments,  the  frequent  plexiform  arrangement  of 
the  branches,  and  their  distribution  to  the  organs  of  circulation  and 
nutrition,  form  a  well-marked  group  of  anatomical  features.  But  not- 
withstanding the  general  importance  of  these  characters,  the  sympa- 
thetic nerves  and  ganglia  do  not  constitute  an  independent  nervous 
system.  Neither  their  anatomical  elements  nor  their  external  connec- 
tions are  essentially  different  from  those  of  the  cerebro-spinal  nerves 
and  centres.  The  sympathetic  trunks  and  branches  contain  medullated 
nerve  fibres  like  those  of  the  spinal  nerves ;  and  its  ganglia  contain 
nerve  cells  with  prolongations  in  the  form  of  axis  cylinders.  The  main 
peculiarity  of  the  sympathetic  .nerve  fibres  is  that  they  are,  as  a  rule, 
of  small  diameter,  though  not  smaller  than  the  average  of  those  in  the 
cerebro-spinal  nerves.  The  cells  of  the  sympathetic  are  also  generally 
small,  never,  according  to  Kolliker,  equalling  the  largest  of  those  in 
the  spinal  cord  or  the  brain ;  and  they  are  also  characterized  by  the 
frequency  with  which  they  send  out  a  single  prolongation,  becoming 
apparently  the  source  of  new  fibres. 

On  the  other  hand,  the  posterior  roots  of  the  spinal  nerves  are  pro- 
vided with  ganglia  similar  to  those  of  the  sympathetic  system.  The 
same  arrangement  exists  in  some  of  the  cranial  nerves,  as  in  the  pneu- 
mogastric,  glossopharyngeal,  and  the  fifth  pair.  Thus  all  the  sensitive 
and  mixed  cerebro-spinal  nerves  contain  fibres  of  ganglionic  origin,  in 
addition  to  those  from  the  brain  and  spinal  cord.  Furthermore,  all  the 
sympathetic  ganglia  receive  filaments  from  the  cerebro-spinal  nerves, 
t  he  (litres  of  which,  there  is  reason  to  believe,  pass  through  the  ganglion 
to  the  peripheral  branches  of  the  sympathetic  system.  This  is  in  lei-red 
from  the  fact  that  many  of  these  fibres  cannot  be  seen  either  to  origin- 
ate or  terminate  in  the  ganglion,  and  also  from  the  paralyzing  elleet 
produced  on  n  mu>eul:ir  organ  supplied  with  sympathetic  fibres,  by 
division  of  the  eerebro-spinal  nerve  which  communicates  with  its 
ganglion.  This  is  especially  shown  by  dilatation  of  the  pupil  follow- 
ing division  of  the  oenloniotorins  nerve,  which  supplies  the  iris  will) 
a  motor  branch  through  the  ophthalmic  ganglion.  The  numerous 
filaments  supplied  by  the  pneunioinistric  nerve  to  the  cardiac  branches 

496 


THE    SYMPATHETIC    SYSTEM.  497 

of  the  sympathetic,  and  to  the  cardiac  plexus,  afford  a  striking  instance 
of  the  same  kind. 

The  ganglia  on  the  spinal  and  cranial  nerve  roots  are  undoubtedly 
analogous,  in  their  anatomical  relations,  to  those  of  the  sympathetic 
system  ;  and  this  system  may  be  considered  as  made  up  of  nervous 
centres  disseminated  through  the  great  cavities  of  the  body,  and  con- 
necting filaments  which  receive  fibres  from  the  cerebro-spinal  nerves 
and  supply  to  these  nerves  fibres  of  their  own.  All  the  organs  in  the 
body,  accordingly,  contain  nerve  fibres  from  both  sources ;  the  differ- 
ence consisting  in  the  relative  numbers  of  one  kind  or  the  other  in  par- 
ticular parts.  The  cerebro-spinal  nerves  are  in  greatest  abundance, 
and  manifest  their  most  striking  properties,  in  the  organs  of  animal 
life ;  those  of  the  sympathetic  system  preponderate  in  the  organs  of 
nutrition,  and  in  their  influence  on  the  functions  of  circulation,  secre- 
tion, and  growth. 

General  Arrangement  of  the  Sympathetic  System.— The  central  part 
of  the  sympathetic  system  is  a  double  chain  of  ganglia,  on  the  sides 
of  the  spinal  column,  united  with  each  other  by  longitudinal  filaments. 
Each  ganglion  is  connected,  by  motor  and  sensitive  fibres,  with  the 
cerebro-spinal  system.  Its  nerves  are  distributed  to  glands  and  mucous 
membranes,  mostly  destitute  of  general  sensibility,  and  to  muscular 
fibres  which  are  independent  of  the  will.  The  sympathetic  ganglia 
are  situated  in  the  head,  neck,  chest,  and  abdomen ;  and  in  each  of 
these  regions  are  connected  by  their  nerves  of  distribution  with  special 
organs. 

The  first  sympathetic  ganglion  in  the  head  is  the  ophthalmic  ganglion, 
in  the  orbit  of  the  eye,  on  the  outer  aspect  of  the  optic  nerve.  It  com- 
municates by  slender  filaments  with  the  carotid  plexus  of  sympathetic 
nerves,  receives  a  motor  root  from  the  oculomotorius,  and  a  sensitive 
root  from  the  ophthalmic  division  of  the  fifth  pair.  Its  filaments  of  dis- 
tribution, known  as  the  "ciliary  nerves,"  pass  forward  upon  the  eye- 
ball, pierce  the  sclerotic,  and  terminate  in  the  iris. 

The  next  is  the  spheno-palatine  ganglion,  in  the  spheno-maxillary 
fossa.  It  communicates,  like  the  preceding,  with  the  carotid  plexus, 
receives  a  motor  root  from  the  facial  nerve,  and  a  sensitive  root  from 
the  superior  maxillary  division  of  the  fifth  pair.  Its  filaments  are  dis- 
tributed to  the  levator  palati  and  uvular  muscles,  to  the  mucous  mem- 
brane of  the  posterior  part  of  the  nasal  passages,  and  to  that  of  the 
hard  and  soft  palate. 

The  third  is  the  submaxillary  ganglion,  connected  with  the  submax- 
illary  gland.  It  communicates  with  the  superior  cervical  ganglion  of 
the  sympathetic  by  filaments  accompanying  the  external  carotid  and 
facial  arteries.  It  derives  its  sensitive  filaments  from  the  lingual 
branch  of  the  fifth  pair,  and  its  motor  filaments  from  the  facial  nerve, 
by  the  chorda  tympani.  Its  branches  of  distribution  pass  mainly  to 
the  submaxillary  gland  and  duct. 

The  last  sympathetic  ganglion  in  the  head  is  the  otic  ganglion,  situ- 

2G 


498 


THE    NERVOUS    SYSTEM. 


FIG.  128. 


atcd  beneath  the  base  of  the  skull,  on  the  inner  side  of  the  inferior  max- 
illary division  of  the  fifth  pair.  It  receives  filaments  of  communication 
from  the  carotid  plexus ;  a  motor  root  from  the  facial  by  the  small  super- 
ficial petrosal  nerve,  as  well  as  one  or  two  short  fibres  from  the  infe- 
rior maxillary  division  of  the 
fifth  pair ;  and  a  sensitive  root 
from  the  glossopharyngeal  by  the 
nerve  of  Jacobson.  Its  branches 
are  sent  to  the  internal  muscle 
of  the  malleus  in  the  middle  ear 
(tensor  tympani),  to  the  circum- 
flexus  palati,  and  to  the  mucous 
membrane  of  the  tympanum  and 
Eustachian  tube. 

The  continuation  of  the  sym- 
pathetic nerve  in  the  neck  con- 
sists of  two  and  sometimes  three 
ganglia,  the  superior,  middle,  and 
inferior,  communicating  with 
each  other  and  the  cervical  spinal 
nerves.  Its  filaments  follow  the 
course  of  the  carotid  artery  and 
its  branches,  forming  by  their 
inosculations  the  corresponding 
arterial  plexuses,  and  supplying 
fibres  of  distribution  to  the  thy- 
roid gland,  the  larynx,  trachea, 
pharynx,  and  oesophagus.  By 
the  superior,  middle,  and  infe- 
rior cardiac  nerves  it  also  sup- 
plies fibres  to  the  cardiac  plexus, 
and  through  it  to  the  heart. 

In  the  chest,  the  communica- 
tions of  the  sympathetic  ganglia 
with  the  spinal  nerves  are  double ; 
each  ganglion  receiving  two  fila- 
ments from  the  intercostal  nerve 
next  above  it.  The  nerves  orig- 
inating from  the  ganglia  are  dis- 
tributed to  the  plexuses  on  the 
thoracic  aorta,  and  to  those  of  the  lungs  and  oesophagus. 

In  the  abdomen,  the  sympathetic  system  consists  mainly  of  an  aggre- 
gation of  gantrlionic  enlargements  situated  on  the  cceliac  artery,  known 
as  the  semilunar  or  ccrliac  ganglion.  From  this  centre  a  multitude 
of  diverging  and  inosculating  branches  are  sent  out,  which,  from  their 
common  origin  and  radiating  course,  are  termed  the  "solar  plexus." 
Its  secondary  plexuses,  accompanying  the  branches  of  the  abdominal 


GANGLIA  AND  NKRVKS  OP  THK  SYMPATHETIC 

SYSTI  M. 


THE    SYMPATHETIC    SYSTEM.  499 

aorta,  are  distributed  to  the  stomach,  intestine,  spleen,  pancreas,  liver, 
kidneys,  supra-renal  capsules,  and  internal  organs  of  generation. 

In  the  pelvis,  there  are  four  or  five  pairs  of  ganglia,  situated  on  the 
anterior  aspect  of  the  sacrum,  and,  at  its  lower  extremity,  the  "  gan- 
glion irnpar,"  which  is  regarded  as  a  fusion  of  two  symmetrical  ganglia. 

In  all  these  parts  a  main  characteristic  of  the  sympathetic  nerves  is 
their  arrangement  in  the  form  of  plexuses,  which  surround  the  arterial 
branches,  and  follow  their  peripheral  distribution  in  the  vascular  organs. 

Sensibility  and  Motor  Power  in  the  Sympathetic  System. 

The  sympathetic  ganglia  and  nerves  are  endowed  both  with  sensi- 
bility and  the  power  of  exciting  motion ;  but  these  properties  are  less 
active  than  in  the  cerebro-spinal  system,  and  are  exercised  in  a  different 
manner.  If  a  motor  or  sensitive  spinal  nerve  be  irritated  by  the 
galvanic  current,  the  evidences  of  pain  or  of  muscular  reaction  are 
decisive  and  instantaneous.  There  is  hardly  an  appreciable  interval 
between  the  application  of  the  stimulus  and  the  sensation  or  motion 
which  results.  But  in  experiments  on  the  sympathetic  nerves,  evi- 
dences of  sensibility,  when  manifested,  are  much  less  acute,  and  show 
themselves  only  after  prolonged  application  of  the  exciting  cause. 

The  same  character  is  exhibited  in  their  motor  action.  If  the  semilunar 
ganglion  or  its  nerves  be  galvanized,  no  immediate  effect  is  visible  ;  but 
after  a  few  seconds  a  slow,  progressive,  vermicular  contraction  takes 
place  in  the  intestine,  and  continues  for  some  time  after  the  galvaniza- 
tion has  ceased. 

Connection  with  the  Special  Senses. — In  the  head,  the  sympathetic  has 
an  important  connection  with  the  special  senses.  This  is  especially 
noticeable  in  the  eye,  from  influences  regulating  the  movements  of 
the  pupil.  The  reflex  action,  by  which  these  movements  take  place, 
is  transmitted  by  the  oculomotorius  nerve  to  the  ophthalmic  ganglion, 
and  thence  by  the  ciliary  nerves  to  the  muscular  fibres  of  the  iris. 

The  movements  of  the  iris  exhibit  consequently  a  somewhat  slug- 
gish character,  which  indicates  the  intervention  of  the  sympathetic 
system.  They  do  not  take  place  instantaneously  with  the  variation 
of  light,  but  require  an  appreciable  interval  of  time  If  both  eyes  be 
closed  and  covered,  long  enough  to  allow  complete  dilatation  of  the 
pupils,  and  then  suddenly  opened,  the  pupils  contract  somewhat  rap- 
idly to  a  certain  extent,  and  afterward  continue  to  diminish  for  several 
seconds,  until  equilibrium  is  fairly  established. 

As  the  movements  of  the  iris  derive  their  stimulus,  through  the 
ophthalmic  ganglion,  from  the  oculomotorius  nerve,  if  this  nerve  be 
divided  between  the  brain  and  the  eyeball,  the  pupil  becomes  sensibly 
dilated,  and  loses  in  great  measure  its  power  of  contraction  under  the 
influence  of  light.  There  is  a  partial  paralysis,  in  which  the  circular 
fibres  of  the  iris  are  relaxed,  while  its  radiating  fibres  continue  to  act, 
causing  enlargement  of  the  pupil. 

On  the  other  hand,  if  the  sympathetic  nerve  be  divided  in  the  neck, 


500  THE    NERVOUS    SYSTEM. 

or  its  superior  cervical  ganglion  extirpated,  the  pupil  on  the  correspond- 
ing side  becomes  contracted  from  paralysis  of  its  radiating  fibres.  In 
quadrupeds,  the  eyeball  is  also  drawn  backward  into  the  orbit,  causing 
partial  closure  of  the  upper  and  lower  eyelids,  and  advance  of  the  third 
eyelid  or  "  nictitating  membrane  "  over  the  cornea.  This  recession  of 
the  eyeball  is  due  to  paralysis  of  a  muscle  composed  of  unstriped  fibres, 
which  exists  in  most  quadrupeds  under  the  name  of  the  "  orbital 
muscle,"  and  which  normally  maintains  the  eyeball  in  a  moderate 
state  of  protrusion.  After  its  paralysis,  the  straight  muscles  of  the 
orbit,  being  no  longer  antagonized,  produce  permanent  retraction  of 
the  eyeball,  and  consequently  partial  closure  of  the  lids.  Both  the 
closure  of  the  lids  and  the  narrowing  of  the  pupil  are  therefore  sec- 
ondary effects  of  division  of  the  sympathetic  nerve. 

But  if,  under  these  circumstances,  the  upper  extremity  of  the  divided 
nerve  be  stimulated  by  faradization,  the  conditions  are  reversed.  The 
eyeball  advances  to  its  former  place  in  the  orbit,  and  the  pupil  con- 
tracts. Both  these  effects  correspond  in  degree  with  the  stimulation 
of  the  nerve.  If  the  electric  current  be  of  moderate  strength,  the  eye 
may  be  simply  restored  for  the  time  to  its  normal  condition.  If  of 
greater  intensity,  it  may  cause  protrusion  of  the  eyeball  and  reduc- 
tion of  the  pupil  to  its  minimum  diameter.  When  faradization  is 
suspended,  the  pupil  again  enlarges,  and  the  eyeball  returns  to  its 
retracted  position. 

It  is  evident,  accordingly,  that  the  muscular  apparatus  of  the  eye  is 
under  the  control  of  two  nervous  influences,  derived  respectively  from 
the  cerebro-spinal  and  the  sympathetic  system.  The  iris  receives  all 
its  motor  fibres  from  the  ophthalmic  ganglion.  But  those  causing  con- 
traction of  the  pupil  come  through  this  ganglion  from  the  oculomo- 
torius  nerve :  those  causing  dilatation  are  derived,  through  the  same 
channel,  from  the  central  ganglia  of  the  sympathetic  system. 

Vasomotor  Nerves  and  Nerve  Centres, 

The  most  important  general  function  of  the  sympathetic  nerves  and 
nerve  centres  is  connected  with  the  blood-vessels  and  the  circulation  in 
different  regions  of  the  body.  Their  filaments  and  plexuses  are  espe- 
cially associated  with  the  arterial  branches,  which  they  follow  in  their 
subsequent  ramification  ;  and  their  terminal  fibres  are  largely  distributed 
to  the  muscular  coat  of  these  vessels.  Under  their  influence  the  muscu- 
lar elements  contract,  thus  approximating  the  walls  of  the  artery,  and 
diminishing  its  calibre.  The  nerves  which  excite  in  this  way  the  con- 
traction of  the  blood-vessels  are  called  "Vasomotor  nerves,"  and  the 
nerve  centres  from  which  they  emanate  "  vasomotor  centres." 

Muscularity  and  Contractility  of  the  Blood-vessels. — So  far  as  their 
structure  is  concerned,  the  arteries  are,  in  great  measure,  muscular 
organs.  Their  middle  coat,  at  least  in  those  of  medium  and  smaller 
size,  contains  unstriped  muscular  fibres  min.irlod  with  elastic  tissue; 
and  the  relative  abundance  of  these  fibres  increases  as  the  size  of  the 


THE    SYMPATHETIC    SYSTEM.  501 

artery  diminishes,  the  middle  coat  of  the  smallest  arterial  branches 
being  almost  exclusively  muscular.  The  fibres  of  this  coat  are  wrapped 
round  the  artery  in  an  annular  direction ;  producing,  when  called  into 
activity  at  any  point,  a  local  constriction  of  the  arterial  tube. 

Furthermore,  it  is  shown  by  observation  that  arteries,  like  other 
muscular  organs,  have  the  power  of  contractility.  Their  contraction 
in  the  living  animal,  under  mechanical  irritation  or  galvanic  stimulus, 
has  been  demonstrated  in  various  observations  quoted  by  Milne  Ed- 
wards,* and  corroborated  by  Yulpian")*  in  more  extended  experiments 
on  the  same  subject.  The  carotid,  femoral,  hypogastric,  interdigital, 
auricular,  and  mesenteric  arteries,  have  all  been  seen  to  contract  when 
touched  with  the  point  of  a  needle,  rubbed  with  a  smooth  instrument, 
or  subjected  to  the  galvanic  current.  There  are  certain  peculiarities 
in  the  phenomena  thus  produced,  showing  a  physiological  relationship 
between  the  arteries  and  other  organs  composed  of  unstriped  muscular 
fibres.  First,  the  contraction  of  the  artery  does  not  take  place  imme- 
diately on  the  application  of  the  stimulus,  but  only  after  a  perceptible 
interval.  According  to  Vulpian,  when  the  electrodes  are  placed  for  a 
few  instants  in  contact  with  an  artery,  no  effect  may  be  visible  on  their 
withdrawal ;  but  after  a  short  time  the  vessel  diminishes  in  size, 
becoming  gradually  smaller  at  the  point  of  stimulation,  until  its 
calibre  is  nearly  or  quite  obliterated.  It  remains  in  this  condition 
for  ten  or  fifteen  seconds,  after  which  it  slowly  enlarges  to  its  previ- 
ous size.  Secondly,  the  contractility  of  the  vascular  walls  under  local 
stimulation  is  more  distinct  in  the  branches  than  in  the  trunks  of  the 
arteries,  and  is  most  pronounced  in  their  smallest  ramifications.  This 
corresponds  to  the  anatomical  structure  of  these  vessels,  in  which  the 
muscularity  of  their  middle  coat  increases  with  their  diminution  in  size. 

The  contraction  of  an  artery  under  these  circumstances  has  an  effect 
on  the  local  circulation.  The  diminished  calibre  of  the  vessel  allows 
a  smaller  quantity  of  blood  to  pass  through  it,  and  thus  produces  a 
partial  anemia  of  the  region  supplied  by  its  branches.  If  this  region 
be  wanting  in  collateral  inosculations,  its  change  in  vascularity  may  be 
very  marked.  All  the  vascular  ramifications  beyond  the  constricted 
portion  of  the  artery  become  comparatively  bloodless ;  and  they  con- 
tinue in  this  condition  until  the  artery  relaxes,  and  again  allows  the 
free  entrance  of  blood.  While  the  entire  system,  therefore,  depends 
on  the  heart  as  an  organ  of  impulsion  for  the  circulation  in  general, 
each  artery  controls,  for  its  own  special  region,  the  quantity  of  blood 
admitted  to  the  capillaries  and  veins. 

Rhythmical  Contraction  of  Arteries  in  Particular  Parts. — If  the 
ear  of  a  white  rabbit  be  held  for  a  few  moments  against  the  light  it 
will  be  seen  that  its  blood-vessels  change  their  appearance  from  time  to 
time,  and  that  this  change  occurs  with  a  certain  regularity.  The  cen- 

*  Lefons  sur  la  Physiologic  et  1'Anatomie  Compare.    Paris,  1859,  tome  iv.,  p.  207. 
f  Lepons  sur  1'Appareil  Vasomoteur.     Paris,  1875,  tome  i.,  p.  43. 


502  THE    NERVOUS    SYSTEM. 

tral  artery,  as  it  passes  from  the  base  of  the  ear  toward  its  apex,  divides 
into  branches  supplying  the  capillary  plexus  ;  and  the  vessels  emerging 
from  this  plexus  unite  in  two  principal  veins,  which  return  along  the 
edges  of  the  organ  toward  its  base.  Both  the  central  artery  with  its 
branches,  and  the  principal  veins,  are  readily  visible  by  transparency, 
while  the  intervening  tissue  has  a  light  rosy  hue,  from  the  blood  in 
the  capillary  circulation.  The  change  in  vascularity,  first  observed  by 
Schiff,*  takes  place  in  the  following  manner  :  The  central  artery  dimin- 
ishes in  size,  becoming  narrower  and  fainter,  until  nearly  invisible  Its 
branches  disappear,  the  ear  generally  becomes  more  pallid,  and  the 
veins,  receiving  from  the  capillaries  a  smaller  quantity  of  blood,  appear 
less  numerous  and  less  distinct.  The  circulation  in  the  organ  is  thus 
reduced  in  quantity  at  least  one-half.  This  condition  lasts  for  eight  or 
nine  seconds,  after  which  the  artery  begins  to  enlarge.  A  thread-like 
stream  of  blood  enters  it  from  below,  increasing  in  thickness  and  capac- 
ity, and  extending  rapidly  upward  into  the  arterial  ramifications.  The 
tissues  regain  their  rosy  color,  and  the  veins  become  prominent  along 
the  edges  of  the  organ.  The  artery  is  then  in  a  state  of  diastole,  sup- 
plying the  ear  with  a  full  quantity  of  blood.  It  remains  in  this  condi- 
tion for  two  or  three  seconds,  when  another  contraction  takes  place, 
and  the  circulation  is  again  reduced.  These  alternations  of  constric- 
tion and  expansion  recur  usually  about  ten  or  twelve  times  per  minute. 
They  are  not  strictly  uniform  either  in  extent  or  frequency,  but  they 
take  place  with  sufficient  regularity  to  show  that  they  are  not  accidental, 
but  depend  on  causes  of  internal  origin. 

It  is  probable  that  other  organs,  if  they  could  be  examined  by  trans- 
parency, would  show  a  similar  variation  in  vascularity.  The  small 
saphenous  artery  in  the  rabbit  has  been  seen  by  Loven,  Riegel,  and 
Yulpian  to  exhibit  alternate  movements  of  constriction  and  dilatation 
once  or  twice  per  minute.  In  examining  the  circulation  in  the  frog's 
foot  under  the  microscope,  the  small  arteries  sometimes  show  a  local 
constriction  by  which  they  are  reduced  in  diameter  for  a  certain  time, 
afterward  enlarging  to  their  former  size ;  and  temporary  changes  of 
vascularity  in  the  glandular  organs  or  the  mucous  membranes  have 
long  been  known  to  take  place  in  connection  with  secretion  or  digestion. 

Contraction  and  Dilatation  of  Arteries  under  Nervous  Influence. — 
When  the  sympathetic  nerve  is  divided  in  the  neck,  one  of  the  most 
immediate  and  striking  effects  is  a  vascular  congestion  in  the  parts 
above,  on  the  corresponding  side.  This  effect  may  be  produced  in 
any  warm-blooded  animal,  but  is  especially  manifest  in  the  ear  of  the 
white  rabbit,  where  the  vascularity  is  easily  examined  by  transparency, 
and  where  the  corresponding  parts  on  the  two  sides  can  be  directly 
compared  with  each  other.  A  few  minutes  after  section  of  the  nerve 
all  the  vessels  of  the  ear  on  the  affected  side  become  turgid  with  blood. 
The  artery  enlarges,  its  branches  become  more  visible,  the  tissues  gen- 

*  Comptes  Rendus  de  l'Acade"niie  des  Sciences.     Paris,  1854,  tome  xxxix  ,  p.  508. 


THE    SYMPATHETIC    SYSTEM.  503 

erally  are  ruddy  in  color,  and  the  marginal  veins  are  increased  in  size ; 
while  many  venous  branches,  which  were  before  imperceptible,  become 
distinctly  apparent.  The  artery  no  longer  exhibits  its  periodical  con- 
strictions, but  remains  in  a  state  of  permanent  diastole,  and  the  quantity 
of  blood  circulating  in  the  ear  is  consequently  increased. 

A  variety  of  secondary  consequences  follow  from  this  condition. 
First,  the  temperature  of  the  ear  is  increased.  A  larger  quantity  of 
blood  from  the  interior  of  the  body,  passing  through  the  vessels,  com- 
municates its  warmth  to  the  tissues  of  the  part,  and  the  elevation  of 
temperature  is  perceptible  both  by  the  touch  and  the  thermometer. 
Secondly,  the  blood  in  the  veins  becomes  brighter,  since  in  its  more 
rapid  passage  through  the  capillaries  it  loses  less  oxygen,  and  con- 
sequently retains  more  nearly  the  hue  of  arterial  blood.  Thirdly,  the 
sensibility  of  the  parts  is  increased  and  reflex  actions  from  irritation  of 
the  integument  are  more  strongly  pronounced. 

These  results  are  not  confined  to  the  ear,  but  extend  to  all  parts  of 
the  head  and  face  on  the  side  of  the  section.  The  skin,  the  conjunctiva, 
the  mucous  membranes  of  the  mouth  and  nasal  passages,  even  the 
meninges  of  the  brain,  and,  according  to  Yulpian,  the  fundus  of  the 
eye  when  examined  by  the  ophthalmoscope,  all  show  an  increased 
vascularity  and  more  abundant  circulation. 

The  phenomena  above  described  are  increased  in  intensity  by  extir- 
pation of  the  superior  cervical  ganglion  of  the  sympathetic.  They  are 
due  to  paralysis  of  the  muscular  coat  of  the  arteries  in  the  regions  sup- 
plied by  sympathetic  filaments  from  this  source.  Owing  to  this  paral- 
ysis, the  arteries  no  longer  offer  their  usual  resistance  to  the  pressure 
of  blood  from  the  heart.  Their  relaxation  admits  a  larger  quantity  to 
the  capillaries  of  the  corresponding  regions,  and  thus  causes  an  in- 
creased local  circulation. 

These  effects  of  division  of  the  sympathetic  are  all  reversed  by  its 
stimulation.  If  the  upper  extremity  of  the  divided  nerve  be  subjected 
to  faradization,  the  arteries  of  the  affected  ear  diminish  in  size,  the 
vascular  congestion  disappears,  and  the  local  temperature  becomes 
reduced  to  its  normal  standard,  or  even  lower.  The  varying  condition 
of  the  blood-vessels  under  nervous  influence  is  shown  by  an  experiment 
of  Bernard,*  in  which  the  upper  part  of  a  rabbit's  ear  is  cut  off  by 
a  clean  incision,  allowing  the  blood  to  escape  in  jets  from  the  divided 
arteries.  The  force  and  height  of  the  jets  having  been  observed,  the 
sympathetic  nerve  is  divided  in  the  neck  on  the  corresponding  side. 
The  blood  at  once  escapes  from  the  wounded  ear  in  greater  abundance, 
and  the  arterial  jets  rise  to  double  or  triple  their  former  height.  The 
galvanic  current  is  then  applied  to  the  nerve,  above  the  point  of 
section,  when  the  streams  of  blood  escaping  from  the  wound  diminish 
or  disappear ;  but  they  recommence  when  the  galvanization  of  the  nerve 
is  suspended. 

*  Journal  de  la  Physiologic.     Paris,  1862,  p.  397. 


50-i  THE    NERVOUS    SYSTEM. 

The  sympathetic  nerves  accordingly  exert  an  influence  on  the  muscu- 
lar coat  of  the  arteries  similar  to  that  of  the  cerebro-spinal  nerves  on 
the  voluntary  muscles.  They  cause  contraction  of  these  vessels,  a  dimin- 
ished flow  of  blood  through  them,  and  consequently  pallor  and  coolness 
in  the  corresponding  parts.  On  the  other  hand,  division  of  these 
nerves  causes  relaxation  of  the  arteries  and  all  the  secondary  results  of 
an  increased  supply  of  blood. 

Centres  of  Origin  of  the  Vasomotor  Nerves.  —  From  facts  above 
detailed  it  is  evident  that  the  vasomotor  nerves  of  the  head  and  face 
come  from  below.  They  ascend  in  the  cervical  portion  of  the  sympa- 
thetic nerve,  and  pass,  through  the  superior  cervical  ganglion,  to  their 
distribution  in  the  blood-vessels.  The  superior  cervical  ganglion  is 
itself,  in  some  degree,  a  source  of  power  for  these  nerves  ;  and  its  extir- 
pation produces  complete  and  durable  vascular  relaxation  in  the  parts 
above.  But  it  receives  at  least  a  portion  of  this  power  from  the 
sympathetic  nerve  in  the  neck  ;  since  division  of  the  nerve  below  the 
ganglion  is  sufficient  to  cause  a  distinct  congestion  in  the  corresponding 
parts. 

The  real  origin  of  the  vasomotor  fibres  of  the  sympathetic  is  in  the 
spinal  cord.  All  the  sympathetic  ganglia,  beside  their  connection  with 
each  other  by  the  longitudinal  filament  of  the  sympathetic  nerve,  are 
connected  with  the  adjacent  spinal  nerves  by  communicating  branches  ; 
and  many  of  the  fibres  composing  these  branches  may  be  traced, 
through  the  spinal  nerve  roots,  to  the  spinal  cord.  Furthermore, 
experiment  also  shows  that  the  spinal  cord  is  the  source  of  nervous 
action  for  the  sympathetic  system. 

This  was  first  proved  by  Budge  and  Waller*  in  regard  to  the  action 
of  the  sympathetic  on  the  radiating  fibres  of  the  iris.  They  found  in 
the  rabbit  a  region  in  the  spinal  cord,  extending  from  the  first  cer- 
vical to  the  sixth  dorsal  vertebra,  within  which  galvanization  pro- 
duces dilatation  of  the  pupil,  as  if  the  sympathetic  itself  had  been  gal- 
vanized ;  but  if  the  sympathetic  be  previously  divided  in  the  neck 
on  one  side,  galvanization  of  the  cord  is  without  effect  on  the  pupil 
of  the  corresponding  eye,  while  it  still  causes  dilatation  on  the  side 
where  the  sympathetic  is  entire.  The  stimulus  therefore  passes,  in 
this  instance,  through  the  spinal  nerve  roots  and  their  branches  to  the 
irsmtflia  at  the  root  of  the  neck,  and  thence  upward,  through  the  cervical 
portion  of  the  sympathetic  to  the  head.  The  part  of  the  spinal  cord 
where  galvanization  produces  its  maximum  effect  on  the  pupil  is  that 
included  between  the  second  and  third  dorsal  vertebra. 

It  was  subsequently  shown  by  Bernard  f  that  the  vasomotor  fibres 
for  the  head  emanate  from  the  spinal  cord  in  the  same  region,  but 
at  a  slightly  different  level  ;  so  that  the  fibres  going  to  the  iris  and 
those  influencing  the  blood-vessels  are  distinct  though  adjacent  in  their 
origin  from  the  cord.  If,  in  the  dog,  the  roots  of  the  first  two  dorsal 
iirrvcsbe  divided  within  the  spinal  canal,  all  the  phenomena  connected 


*  (  'oiiiptr*  lu-mliis  <]«•  1'  Ara.lriim-  »K's  Sru-nces.     Paris,  iSol,  tome  xxxiii.,  p.  372. 
tlbul.,  1SIJ2,  tome  lv.,  p.  383. 


THE    SYMPATHETIC    SYSTEM.  505 

with  the  pupil  and  eyeball  follow  in  the  same  way  as  if  the  sympathetic 
had  been  cut  in  the  neck,  but  there  is  no  vascular  congestion  or  in- 
creased temperature  of  the  parts ;  and  galvanization  of  the  peripheral 
extremities  of  the  divided  nerve  roots,  causes  dilatation  of  the  pupil, 
like  galvanization  of  the  sympathetic  in  the  neck.  On  the  other 
hand,  if  the  trunk  of  the  sympathetic  be  divided  in  the  upper  part  of 
the  chest,  between  the  heads  of  the  second  and  third  ribs,  there  is  no 
contraction  of  the  pupil,  but  the  temperature  of  the  ear  is  increased 
from  4°  to  6°  C.  above  that  of  the  opposite  side. 

There  is  accordingly  a  remarkable  difference  between  the  nerve  fibres 
for  sensation  and  voluntary  motion  and  those  for  the  blood-vessels  in 
the  route  which  they  follow  to  their  distribution  in  the  head.  The 
sensitive  and  motor  nerves  of  the  head  and  face  emerge  from  the  base 
of  the  brain  and  pass,  through  the  cranial  foramina,  to  the  integument 
and  muscles.  Those  destined  for  the  blood-vessels  are  given  off  from 
the  spinal  cord,  mainly  with  the  roots  of  the  third  pair  of  dorsal  nerves, 
whence  they  join  the  sympathetic,  passing  upward  through  its  cervical 
portion  to  the  head  and  face. 

There  is  also  a  difference  of  origin,  though  less  marked,  between  the 
fibres  for  sensation  and  volition  and  those  for  vasomotor  action  in  the 
limbs.  The  vasomotor  fibres  for  the  upper  limb  do  not  originate 
with  the  nerve  roots  going  to  form  the  brachial  plexus,  but  farther 
down,  in  the  dorsal  portion  of  the  cord.  Bernard  found  that,  in  the 
dog,  division  of  the  last  three  cervical  and  first  two  dorsal  nerves  within 
the  spinal  canal  causes  paralysis  of  'motion,  and  sensation  in  the  cor- 
responding foreleg,  but  no  vascular  congestion  or  calorification.  On 
the  other  hand,  extirpation  of  the  first  thoracic  ganglion  of  the  sym- 
pathetic, or  section  of  the  nerves  of  the  brachial  plexus  after  they  have 
been  joined  by  filaments  from  this  ganglion,  causes  an  elevation  of  tem- 
perature in  the  corresponding  limb ;  and  the  samo  result  follows  divi- 
sion of  the  thoracic  portion  of  the  sympathetic  between  the  third  and 
fourth  dorsal  vertebrae.  The  vasomotor  fibres  paralyzed  by  this  section 
come  therefore  from  below  the  first  thoracic  ganglion ;  and,  according 
to  Cyon,  they  emanate  from  the  spinal  cord  with  the  roots  of  the  dorsal 
nerves,  from  the  third  to  the  seventh  pairs  inclusive. 

The  vasomotor  fibres  for  the  lower  limb  have  a  similar  origin.  Ac- 
cording to  Bernard,  section  of  the  spinal  nerve  roots  destined  for  the 
lumbo-sacral  plexus,  in  the  dog,  paralyze  the  corresponding  hind  leg 
without  causing  increase  of  temperature ;  but  the  latter  effect  is  pro- 
duced in  addition  by  dividing  the  sympathetic  at  the  level  of  the  fifth 
and  sixth  lumbar  vertebra,  or  by  section  of  the  sciatic  nerve.  The 
vasomotor  fibres  of  the  limbs  are  therefore  distinct  from  those  which 
supply  them  with  ordinary  motion  and  sensibility. 

Tonic  Contraction  of  Blood-vessels  and  its  Influence  on  the  Circu- 
lation.— Under  the  stimulus  of  the  sympathetic  fibres  distributed  to 
the  arterial  walls,  the  vessels  are  normally  maintained  in  a  moderate 
state  of  contraction.  This  continuous  muscular  activity  is  the  "  tone  " 
or  tonic  contraction  of  the  arteries,  by  which  they  offer  a  certain  resist- 


506  THE    NERVOUS    SYSTEM. 

ance  to  the  pressure  of  the  blood.  The  blood  moves  accordingly  under 
the  influence  of  two  opposite  forces,  namely:  First,  the  cardiac  im- 
pulse, which  tends  to  urge  it  rapidly  through  the  circulation ;  and 
secondly,  the  tonic  arterial  resistance,  which  tends  to  delay  its  passage 
into  the  capillary  vessels.  The  tonic  arterial  contraction  varies  with 
the  nervous  influences  which  control  it;  and  in  this  way  the  local 
activity  of  the  circulation  is  increased  or  diminished.  There  appears 
to  be  furthermore  a  compensating  action  in  this  respect,  between  the 
blood-vessels  of  different  parts.  When  the  arteries  of  one  organ  are 
contracted,  diminishing  the  quantity  of  blood  which  it  contains,  vascu- 
lar pressure  must  be  increased  in  the  neighboring  parts,  unless  a  pro- 
portionate enlargement  of  their  blood-vessels  restores  the  normal  rela- 
tion between  them.  But  when  the  vascular  tone  is  abolished  in  any 
region  by  division  of  its  sympathetic  nerves,  its  blood-vessels  yield  to 
the  pressure  of  the  rest  of  the  arterial  system,  and  remain  in  a  state 
of  turgescence  and  relaxation. 

Dilator  Nerves. — Beside  the  nerve  fibres  which  cause  contraction 
of  the  blood-vessels,  there  are  others  which  cause  their  dilatation.  The 
latter  class,  which,  from  their  mode  of  action,  are  called  "dilator 
nerves,"  do  not  all  pass  through  the  sympathetic  system,  but  are  dis- 
tributed from  the  cerebro-spinal  nerves  to  the  vascular  organs. 

The  most  striking  and  earliest  known  instance  of  the  action  of  a 
dilator  nerve  is  that  of  the  pneumogastric  in  connection  with  the  heart 
(page  489).  This  action  is  characterized  essentially  as  follows :  1st. 
Galvanization  of  the  nerve  causes  relaxation  of  the  heart,  and  conse- 
quently its  dilatation  by  blood  flowing  in  from  the  large  veins  ;  2d.  If 
the  nerve  be  divided  and  galvanization  applied  to  its  peripheral  extrem- 
ity, the  same  effect  is  produced,  showing  that  the  influence  is  direct  in 
its  operation,  following  a  centrifugal  course  through  the  nerve  to  the 
heart. 

A  similar  action  is  exerted  on  the  circulation  in  the  tongue  and  sub- 
maxillary  gland.  These  observations,  first  made  by  Bernard,*  have 
been  corroborated  and  extended  by  subsequent  experimenters,  and 
especially  by  Vulpian.f 

The  vascular  supply  of  the  tongue  and  submaxillary  gland  receives 
nerve  fibres  from  two  sources,  namely :  1st,  sympathetic  fibres  coming 
from  the  carotid  plexus  and  passing  with  the  arterial  branches  to  their 
distribution  ;  and  2d,  fibres  coming  from  the  facial  nerve  through  the 
chorda  tympani,  which  join  the  lingual  branch  of  the  fifth  pair,  and 
are  thence  distributed  to  the  tongue  and  submaxillary  gland.  The 
influences  exerted  by  these  two  sets  of  fibres  on  the  vascularity  of  the 
parts  are  the  opposite  of  each  other.  Section  of  the  sympathetic- 
filaments  causes  relaxation  of  the  blood-vessels,  increased  circulation, 
ruddy  color  of  the  venous  blood,  and  abundant  salivary  secretion; 
while  galvanization  of  their  peripheral  extremity  produces  contraction 
"/ 

*  Lecons  BUT  les  Liquidea  <lr  rOrjj.-misim-.     Paris,  1X."><),  tome  i.,  p.  31 '_'. 
f  Le9ona  sur  1'Apparcil  Vasomotuur.     Paris,  1875,  tome  i.,  p.  153. 


THE    SYMPATHETIC    SYSTEM.  507 

of  the  blood-vessels  and  general  reversal  of  the  foregoing  results.  But 
if  either  the  lingual  nerve,  or  the  chorda  tympani  above  its  junction, 
be  divided,  the  effect  is  a  diminution  of  the  circulatory  current  both  in 
the  tongue  and  submaxillary  gland.  On  the  other  hand,  galvanization 
of  the  peripheral  extremities  of  these  nerves  causes  dilatation  of  the 
blood-vessels,  and  all  the  phenomena  of  increased  circulation. 

It  must  be  admitted,  accordingly,  that  the  dilator  nerves  exert  a 
direct  local  influence  which  causes  relaxation  of  the  blood-vessels. 
The  mechanism  of  this  influence  is  not  easily  understood ;  since  the 
only  muscular  fibres  connected  with  the  arteries  surround  them  in  a 
circular  direction,  and  could  produce  by  their  contraction  no  other 
effect  than  a  narrowing  of  the  arterial  tube.  The  action  of  the  dilator 
nerves  can  only  be  explained  as  an  "action  of  arrest."  They  convey 
from  the  nervous  centres  outward  an  influence  which  for  the  moment 
interrupts  the  tonic  contraction  of  the  blood-vessels.  Owing  to  this 
suspension  of  tonicity,  the  vessels  dilate  under  the  pressure  of  the 
blood,  and  allow  it  to  circulate  in  larger  quantity.  When  the  suspen- 
sive action  is  terminated,  the  normal  stimulus  of  the  sympathetic  fibres 
restores  the  tonicity  of  the  blood-vessels,  and  the  circulation  returns  to 
its  ordinary  condition. 

The  action  of  arrest,  as  a  nervous  phenomenon,  is  not  confined  to  the 
vascular  system.  All  the  sphincters  exhibit  it  in  a  marked  degree. 
These  muscles  are  habitually  in  a  state  of  tonic  contraction,  by  which 
they  keep  the  outlets  of  the  body  closed  without  voluntary  effort. 
But  when  evacuation  of  the  rectum  or  bladder  is  to  take  place,  the 
first  step  in  the  process  is  an  influence  proceeding  from  the  spinal  cord, 
which  suspends  the  contraction  of  the  sphincters ;  and  after  their  relaxa- 
tion, the  expulsion  of  the  urine  or  feces  is  effected  by  other  muscles. 
Wherever  antagonistic  muscles  exist,  it  is  evident  that  the  contraction 
of  one,  to  be  effective,  must  be  accompanied  by  the  relaxation  of  its 
opposite ;  and  in  all  voluntary  movements,  the  relaxation  of  one  set 
of  muscles  is  as  prompt  and  as  accurately  adjusted  as  the  contraction 
of  the  other.  It  is  probable  that  the  action  of  arrest  plays  an  impor- 
tant part  in  the  nervous  operations  generally  ;  but  it  is  most  distinctly 
manifest  in  the  dilator  nerves  of  the  vascular  system. 

Reflex  Contraction  and  Dilatation  of  the  Blood-vessels. — Thus  far 
the  variations  in  calibre  of  the  blood-vessels  have  been  shown,  in  exper- 
imental observations,  to  depend  on  the  immediate  action  of  the  vasomotor 
and  dilator  nerves.  But  in  the  living  body  these  variations  are  habit- 
ually reflex  in  their  mode  of  production.  The  vascular  contraction  or 
dilatation  which  shows  itself  in  a  particular  area,  is  due  to  the  impres- 
sion received  by  a  sensitive  surface,  conveyed  inward  to  some  nervous 
centre  of  the  vasomotor  system,  and  thence  reflected  in  a  centrifugal 
direction  to  the  blood-vessels.  The  most  frequent  instance  of  reflex 
vascular  constriction  is  that  which  follows  irritation  of  the  central 
extremity  of  a  sensitive  nerve.  This  effect  has  been  observed  by 
many  experimenters,  and  is  regarded  as  nearly  invariable.  Galvaniza- 
tion of  the  central  extremity  of  the  sciatic  nerve  causes  general  con- 


508  THE    NERVOUS    SYSTEM. 

striction  of  the  blood-vessels  throughout  other  parts  of  the  body,  indi- 
cated by  increased  arterial  pressure.  A  similar  result  is  produced  by 
irritation  of  the  trigeminus  or  other  sensitive  nerves  or  nerve  roots, 
or  by  that  of  extended  regions  of  the  integument.  According  to  Vul- 
pian,*  this  effect  is  very  observable,  in  dogs,  on  the  under  surface  of 
the  tongue  after  division  of  one  sciatic  nerve.  On  galvanizing  the 
upper  extremity  of  the  nerve,  the  under  surface  of  the  tongue  grows 
paler,  and  its  superficial  veins  dimmish  visibly  in  size,  or  even  become 
imperceptible.  This  action,  which  is  first  conveyed  by  the  sciatic  nerve 
to  the  spinal  cord,  is  finally  transmitted  to  the  tongue  through  the 
fibres  of  the  sympathetic ;  since  if  the  sympathetic  be  divided  in  the 
cervical  region,  the  above  results  are  no  longer  produced  on  that  side 
from  irritation  of  the  sciatic  nerve. 

Reflex  dilatation  of  the  blood-vessels  is  also  of  frequent  occurrence. 
It  is  distinctly  manifested  in  the  rabbit's  ear  on  galvanizing  the  central 
extremity  of  the  anterior  cervico-auricular  nerve  after  its  division.  This 
effect,  formerly  observed  by  Schiff  and  Rouget,  is,  according  to  Vulpian, 
one  of  the  easiest  to  reproduce;  especially  if  the  animal  be  first  poisoned 
by  woorara,  which  suspends  the  action  of  the  voluntary  muscles,  and 
prevents  their  interfering  with  the  blood-vessels  by  local  contraction. 
Reflex  vascular  dilatation  is  also  the  usual  accompaniment  of  local 
injuries  or  irritations.  Congestion  soon  shows  itself  in  the  neighbor- 
hood of  any  wound  in  the  integument  or  subcutaneous  tissues  ;  and  the 
intestines,  when  exposed  by  opening  the  abdominal  cavity,  become 
rapidly  covered  with  an  increased  vascularity. 

The  most  familiar  examples  of  reflex  dilatation  are  those  occurring 
in  the  glands  and  mucous  membranes  at  the  time  of  their  functional 
excitement.  These  organs  present  alternate  conditions  of  repose  and 
activity.  In  the  former  condition  their  blood-vessels  are  moderately 
contracted,  supplying  blood  in  small  quantity  for  the  nutrition  of  the 
glandular  tissues,  or  for  the  preparation  of  their  special  organic  ingre- 
dients. But  when  the  period  arrives  for  active  secretion,  there  is  a 
dilatation  of  the  blood-vessels,  with  increased  local  circulation  and  free 
exudation  of  the  secreted  fluids.  This  phenomenon  was  witnessed  in 
the  mucous  membrane  of  the  stomach,  so  long  ago  as  in  the  obser- 
vations of  Beaumont*  on  the  gastric  fistula  of  Alexis  St.  Martin ;  and 
it  has  subsequently  been  observed  in  many  similar  cases.  In  the  sub- 
maxillary  gland  of  the  dog,  reflex  vascular  congestion  is  at  once  pro- 
duced by  introducing  vinegar  into  the  mouth,  or  by  any  stimulus 
which  excites  the  salivary  secretion.  A  similar  variation  was  found 
by  Bernard  in  the  vascularity  of  the  pancreas  and  duodenum,  in  the 
dog,  under  the  conditions  of  fasting  and  digestion.  In  the  intervals 
of  digestion  these  organs  are  pallid,  with  but  few  blood-vessels  visible 
upon  their  surface.  But  after  the  introduction  of  food,  and  while 
digestion  is  going  on,  their  appearance  is  greatly  changed.  The 

*  Lecons  sur  1'Appareil  Vasoraoteur.     Paris,  1875,  tome  i.,  p.  238. 

f  Experiments  and  Observations  upon  the  Gastric  Juice.     Boston,  1834. 


THE    SYMPATHETIC    SYSTEM.  509 

smaller  arteries  are  more  abundantly  visible,  their  curvatures  more 
pronounced,  and  their  pulsations  more  strongly  marked.  The  super- 
ficial veins  are  also  increased  in  size  and  apparent  numbers,  and  the 
intervening  tissues  have  a  ruddy  color,  due  to  the  abundant  circulation 
in  their  capillary  vessels.  This  condition  lasts  for  a  certain  time,  while 
secretion  and  digestion  are  in  progress ;  after  which  it  gradually  subsides, 
and  the  circulation  returns  to  its  former  state  of  comparative  inactivity. 

It  is  evident  that  these  reflex  actions  take  place  in  some  nervous  cen- 
tre, in  which  the  centripetal  impression  is  converted  into  a  centrifugal 
impulse.  It  appears  that  the  ganglia  of  the  sympathetic  system  act  in 
some  measure  as  nervous  centres  for  this  purpose.  This  is  indicated 
by  the  fact  that  the  vascular  paralysis  of  the  head  and  face,  following 
division  of  the  sympathetic  nerve  in  the  neck,  is  more  pronounced  if 
the  superior  cervical  ganglion  be  extirpated ;  and,  as  a  general  rule, 
removal  or  destruction  of  the  sympathetic  ganglia  produces  more  effect 
than  simple  section  of  the  nerve  trunk.  According  to  Yulpian,  after 
removal  of  the  entire  brain  and  the  upper  half  of  the  spinal  cord, 
including  the  origin  of  the  brachial  nerves,  in  the  frog,  extirpation  of 
the  cervical  ganglion  of  the  sympathetic  is  followed  by  vascular  con- 
gestion of  the  corresponding  half  of  the  tongue  and  buccal  cavity.  The 
sympathetic  ganglia  have  therefore  a  certain  influence  as  the  sources 
of  nervous  power  for  vascular  parts. 

But  the  action  of  these  ganglia  is  limited  in  importance,  and  affects 
only  the  parts  to  which  their  fibres  are  directly  distributed.  It  has 
already  been  shown  that  the  roots  of  the  sympathetic  system  emanate 
from  the  spinal  cord,  and  that  they  emerge  from  it  at  special  points  for 
the  head  and  limbs  respectively.  There  is  reason  to  believe  that  they 
traverse  the  cord  for  some  distance  before  detaching  themselves  from 
its  surface,  and  that  their  source  in  the  gray  substance  is  at  a  higher 
level.  According  to  numerous  observers,  a  transverse  section  of  the 
cord  in  the  cervical  region  causes  marked  vascular  relaxation  through- 
out the  body,  as  if  all  the  vasomotor  fibres  had  been  divided  in  descend- 
ing from  above.  This  effect  is  produced  by  transverse  sections  of  the 
cerebro-spinal  axis  at  any  level  in  the  cervical  portion  of  the  cord  or  in 
the  medulla  oblongata,  nearly  to  the  posterior  edge  of  the  tubercula 
quadrigemina ;  but  not  by  sections  above  that  point.  It  is  accordingly 
maintained  by  some  physiologists  (Schiff,  Owsjannikow,  Liegeois)  that 
there  is  a  common  centre  for  all  the  vasomotor  fibres  of  the  body, 
situated  in  the  medulla  oblongata  or  immediately  above.  In  the  opinion 
of  others  (Brown-Sequard,  Vulpian)  the  vasomotor  centres  are  more 
widely  scattered  in  the  cerebro-spinal  axis ;  since  reflex  modifications 
of  vascularity  may  still  be  produced  to  some  extent  after  division  of 
the  spinal  cord  in  the  cervical  region,  and  even  certain  lesions  in  the 
cerebral  hemispheres  seem  to  produce  vascular  congestion  in  the  limbs 
or  internal  organs.  This  question  is  not  positively  determined ;  but 
it  appears  certain  that  the  main  centres  of  reflex  action  for  the  vascular 
system  are  in  the  cerebro-spinal  axis,  whence  their  nerve  fibres  are 
distributed,  by  various  routes,  to  all  parts  of  the  body. 


CHAPTER   VIII. 
THE   SENSES. 

THE  senses  are  the  endowments  by  which  we  gain  perception  of 
external  objects  and  phenomena.  They  are  consequently  the  primi- 
tive source  of  all  information,  and  the  channels  of  all  conscious  relation 
with  the  external  world.  The  term  sensation  indicates  the  perception 
of  any  impression  from  without,  of  whatever  nature.  The  senses,  on 
the  other  hand,  are  subdivisions  of  the  main  function,  each  devoted  to 
a  particular  class  of  phenomena.  They  are  five  in  number,  namely : 
1.  General  sensibility.  2.  The  sense  of  taste.  3.  The  sense  of  smell. 
4.  The  sense  of  sight.  5.  The  sense  of  hearing. 

General  Sensibility. 

General  sensibility  is  the  faculty  by  which  we  appreciate  the  simpler 
physical  properties  of  external  objects,  such  as  their  consistency,  sur- 
face, temperature,  and  mass.  It  exists  throughout  the  general  integu- 
ment, and  in  the  mucous  membranes  near  the  exterior.  Notwithstand- 
ing that  it  includes  several  different  impressions,  they  are  all,  so  far  as 
we  know,  communicated  by  the  same  nerves ;  and  the  grade  of  sensi- 
bility for  all  varies  in  the  same  direction  and  to  the  same  degree  in 
different  parts  of  the  body.  The  sensations  thus  produced,  though 
presenting  certain  differences  from  each  other,  are  therefore  associated 
under  the  head  of  general  sensibility. 

Sense  of  Touch. — This  is,  perhaps,  the  simplest  form  of  sensory  im- 
pression, and  is  known  as  "tactile  sensibility."  It  is  produced  by  the 
contact  of  foreign  bodies  with  the  sensitive  surface,  and  gives  informa- 
tion as  to  their  solidity,  configuration,  and  indifferent  or  irritating  quali- 
ties. There  is  a  certain  variety  in  these  impressions,  but  they  evidently 
belong  to  the  same  group.  There  is  no  essential  difference  in  the 
effect  of  sharp-pointed  instruments  or  irritating  substances  applied  to 
the  skin,  the  passage  of  the  galvanic  current,  pungent  liquids  in  con- 
tact with  the  tongue,  or  pungent  vapors  in  the  nasal  passages.  They 
are  all  impressions  of  tactile  sensibility,  and  depend  on  a  similar  irri- 
tation of  the  nervous  extremities. 

The  grade  of  tactile  sensibility  varies  in  different  regions.  The  method 
adopted  for  appreciating  this  variation  consists  in  applying  to  the  skin 
or  mucous  membrane  the  points  of  a  pair  of  compasses,  tipped  with 
>in:ill  pieces  of  cork.  If  the  two  points  be  a  very  short  distance  apart, 
they  cannot  be  accurately  distinguished  from  each  other,  and  the  two 
sensations  are  blended  into  one.  The  minimum  distance  at  which  the 

510 


THE    SENSES.  511 

points  can  be  distinguished  thus  indicates  the  grade  of  sensibility  at 
that  spot.  The  observations  of  Valentin*  give  the  following  as  the 
limits  of  distinct  perception  in  different  regions : 

DISTANCE  AT  WHICH  Two  POINTS  MAT  BE  SEPARATELY  DISTINGUISHED. 

At  the  tip  of  tongue 1.00  millimetre. 

"       palmar  surface  of  tips  of  fingers  .         .       1.50  " 

"        of  second  phalanges      .       3.24  " 

"        of  first  phalanges  .       3.44  " 

"       dorsum  of  tongue 5.22  " 

"       dorsal  surface  of  fingers        .         .         .8.12  " 

"       cheek 9.46  " 

"       back  of  hand 14.50  " 

"       skin  of  throat 1V.2T  " 

"       dorsum  of  foot 26.10  " 

"       front  of  sternum 33.0V  " 

"       middle  of  back      ..'...     50.43  " 

This  method  does  not  necessarily  measure  the  acuteness  of  sensi- 
bility, since  the  two  points  might  be  less  easily  distinguished  from  each 
other  in  any  one  region,  and  yet  the  intensity  of  the  sensation  produced 
might  be  as  great  as  in  the  surrounding  parts ;  but  it  affords  an  esti- 
mate of  the  delicacy  of  tactile  sensation,  by  which  we  distinguish 
slight  inequalities  of  surface  in  foreign  bodies.  There  is  reason,  how- 
ever, to  believe  that  the  two  qualities  correspond  with  each  other  in 
development  in  various  localities ;  and  tactile  sensibility  is  frequently 
found  to  be  most  delicate  where  the  amount  of  sensation  is  also  greatest. 
A  feeble  galvanic  current  may  be  perceived  at  the  tips  of  the  fingers, 
though  it  may  produce  no  impression  on  the  limbs  or  trunk ;  and  one 
too  faint  to  be  distinguished  by  the  fingers  may  be  perceptible  at  the 
tip  of  the  tongue. 

Certain  parts  of  the  body,  furthermore,  are  especially  suitable  for 
organs  of  touch,  not  only  from  their  acute  sensibility,  but  also  on 
account  of  their  conformation  and  mobility.  In  man,  the  hands  are 
the  most  favorably  constructed  for  this  purpose,  owing  to  the  varied 
movement  of  the  fingers,  by  which  they  may  be  applied  to  surfaces  of 
any  form,  and  brought  successively  in  contact  with  all  their  parts. 

In  some  animals,  the  long  bristles  on  the  lips  are  used  for  this  pur- 
pose, each  bristle  being  connected  at  its  base  with  a  nervous  papilla ; 
and  in  the  elephant  the  end  of  the  nose,  developed  into  a  flexible  and 
sensitive  proboscis,  is  the  principal  organ  of  touch.  This  function, 
therefore,  may  be  performed  by  any  part  of  the  body  where  the  acces- 
sory organs  are  sufficiently  developed. 

In  the  head  and  face,  the  sensibility  of  the  skin  is  dependent  on  the 
branches  of  the  fifth  pair.  In  the  body  and  limbs  it  is  due  to  the  sen- 
sitive fibres  of  the  spinal  nerves.  It  exists,  to  a  considerable  extent,  in 
the  mucous  membranes  of  the  mouth  and  nose,  and  other  passages 

*  Todd's  Cyclopaedia  of  Anatomy  and  Physiology,  vol.  iv.,  article  Touch. 


512  THE    NERVOUS    SYSTEM. 

leading  to  the  interior.  Sensibility  is  most  acute  in  mucous  mem- 
branes supplied  by  the  fifth  pair,  namely,  in  the  conjunctiva,  anterior 
part  of  the  nares,  inside  of  the  lips  and  cheeks,  and  the  anterior  two- 
thirds  of  the  tongue.  It  diminishes  from  without  inward,  and  disap- 
pears altogether  in  the  internal  organs  not  abundantly  supplied  with 
cerebro-spinal  nerves. 

Sensations  of  Temperature.— The  appreciation  of  temperature  is,  in 
general,  most  highly  developed  in  parts  which  have  the  greatest  tactile 
sensibility.  The  difference  in  this  respect  between  the  sensitive  integu- 
ment of  the  face  and  the  comparatively  insensible  scalp  is  very  marked  ; 
and  hot  applications  may  be  readily  borne  by  the  scalp  which  would  be 
intolerable  upon  the  face.  The  extent  of  surface  exposed  has  also  an 
influence  on  the  effect  produced  by  temperature  ;  and  a  moderate  degree 
of  warmth  or  cold  applied  over  a  large  area  is  more  readily  perceived 
than  if  confined  to  a  limited  region.  There  is  evidence  that  the  im- 
pressions of  temperature  and  those  of  touch  are  either  transmitted  by 
different  nerve  fibres,  or  depend  on  different  forms  of  nervous  excite- 
ment ;  since,  according  to  Brown-Sequard,*  there  are  instances  in  which 
the  two  kinds  of  sensibility  are  impaired  independently  of  each  other. 
In  some  forms  of  paralysis,  tactile  sensibility  may  be  lost  while  that 
of  temperature  remains ;  or,  on  the  other  hand,  the  power  of  appreci- 
ating temperature  may  disappear  while  impressions  of  contact  are  still 
perceived. 

Sensations  of  Pain. — The  sense  of  pain  is  different  in  character  from 
that  caused  by  tactile  impressions  or  variations  in  temperature.  It  is 
produced  by  exaggerated  mechanical  irritation  or  by  excessive  heat  or 
cold ;  and  in  most  instances,  when  the  intensity  of  an  impression  rises 
above  a  certain  point,  the  ordinary  perceptions  disappear,  and  that  of 
pain  takes  their  place.  Thus  if  the  blade  of  a  knife  or  the  point  of  a 
needle  be  placed  gently  in  contact  with  the  skin,  we  perceive,  by  tactile 
sensibility,  its  qualities  of  form  and  surface.  But  if  the  pressure  be 
increased  beyond  a  certain  degree,  or  if  the  integument  be  wounded, 
we  have  no  further  perception  of  the  physical  properties  of  the  foreign 
body,  and  are  only  conscious  of  the  pain  which  it  inflicts.  The  appre- 
ciation of  cold  or  warmth,  in  like  manner,  is  only  possible  within  mod- 
erate limits ;  and  when  either  is  so  excessive  as  to  produce  pain,  all 
accurate  notion  of  the  degree  of  temperature  is  lost.  The  contact  of  a 
red-hot  iron  and  that  of  one  much  below  the  freezing-point  of  water 
produce  sensations  not  essentially  different  from  each  other,  and  marked 
only  by  their  painful  character. 

The  sense  of  pain  may  be  preserved  or  lost  independently  of  other 
kinds  of  sensibility.  The  anaesthesia  produced  by  ether  or  chloro- 
form may  be  carried  to  such  a  point  that  the  capacity  for  feeling  pain 
is  abolished,  while  tactile  sensibility  remains ;  and  in  this  condition  the 

*  Physiology  and  Pathology  of  the  Central  Nervous  System.  Philadelphia,  1860, 
pp.  84,  98, 125. 


THE    SENSES.  513 

wounds  caused  by  puncturing  or  cutting  instruments  may  be  felt,  un- 
accompanied by  any  sense  of  suffering.  Similar  observations  have  been 
made  in  cases  of  paralysis,  where  the  patient  can  sometimes  perceive  the 
contact  of  foreign  bodies  without  experiencing  any  painful  sensation ; 
or,  on  the  other  hand,  the  sense  of  pain  may  persist,  while  that  of 
touch  is  diminished  or  lost.  Notwithstanding  this  apparent  indepen- 
dence of  the  necessary  conditions  for  the  sensation  of  pain,  it  is  trans- 
mitted by  the  same  nerves  which  convey  ordinary  impressions ;  and 
those  which,  like  the  branches  of  the  fifth  pair,  are  endowed  with  the 
most  acute  tactile  sensibility,  are  also  capable,  in  injury  or  disease,  of 
giving  rise  to  the  severest  painful  impressions. 

Mode  of  Action  of  the  Senses  in  general. — There  are  certain  facts 
connected  with  general  sensibility,  and  common  to  the  operation  of  all 
the  senses,  which  are  of  sufficient  importance  to  be  considered  by  them- 
selves. 

In  the  first  place,  an  impression  of  any  kind,  made  upon  a  sensitive 
organ,  remains  for  a  time  after  the  removal  of  its  exciting  cause. 
The  excitement  produced  in  the  nerve  fibres  has  a  certain  persistence, 
which  is  longer  in  some  cases  than  in  others,  but  which  exists  to  some 
extent  in  all.  The  pressure  of  a  foreign  body  upon  the  skin,  especially 
if  somewhat  forcible  and  continued,  is  felt  for  a  perceptible  interval  after 
the  foreign  body  is  removed.  The  sense  of  cold  or  warmth,  fro«m  the 
contact  of  ice  or  heated  liquids,  lasts  more  or  less  after  their  application 
is  discontinued.  Even  for  the  senses  of  sight  and  hearing,  the  same 
fact  may  be  verified;  and  the  duration  of  the  nervous  impression,  though 
very  short,  has  been  found  susceptible  of  measurement. 

Secondly,  the  organs  of  sense  after  a  time  become  accustomed  to  a 
continued  impression,  so  that  it  is  no  longer  perceived.  If  a  uniform 
pressure  be  exerted  on  any  part  of  the  bod}^  it  at  last  fails  to  attract 
notice,  and  we  become  unconscious  of  its  existence.  In  order  to  again 
excite  a  sensation,  the  pressure  must  be.  increased  or  diminished,  or 
changed  in  locality  or  direction. 

The  olfactory  apparatus  also  becomes  habituated  to  odors,  whether 
agreeable  or  disagreeable.  A  continuous  and  uniform  sound,  like  the 
rumbling  of  carriages,  or  the  hissing  of  boiling  water,  becomes  after  a 
time  inaudible ;  but  when  the  sound  ceases  our  attention  is  excited 
by  the  change.  The  senses,  accordingly,  receive  their  stimulus  as 
much  from  the  variation  and  contrast  of  external  impressions  as  from 
the  impressions  themselves. 

Sense  of  Taste. 

The  sense  of  taste  is,  in  some  measure,  intermediate  in  character 
between  general  and  special  sensibility.  The  organ  by  which  it  is 
exercised  is  furnished  with  vascular  and  nervous  papillae  analogous  to 
those  of  the  general  integument.  Its  mucous  membrane  is  also  endowed 
with  general  sensibility.  Although  it  is  highly  probable  that  certain 
minute  formations  in  its  epithelial  layer,  known  as  "taste  buds,"  may 

2H 


f>U  THE    NERVOUS    SYSTEM. 

be  especially  connected  with  the  perception  of  savors,  there  is  thus  far 
no  certainty  in  this  respect ;  and  in  any  case  the  tactile  and  gustatory 
sensibilities  are  closely  intermingled  in  the  mucous  membrane.  The 
sensibility  of  taste,  furthermore,  is  not  confined  to  the  fibres  of  a  single 
nerve,  but  resides  in  portions  of  two,  which  also  supply  general  sensi- 
bility to  the  corresponding  parts ;  and  lastly,  though  some  gustatory 
impressions  are  of  a  distinctly  special  character,  others,  like  the  taste  of 
oily  or  mucilaginous  substances,  differ  but  little  from  those  of  tactile 
sensibility. 

The  sense  of  taste  is  localized  in  the  mucous  membrane  of  the  tongue, 
the  soft  palate,  and  the  pillars  of  the  fauces.  The  tongue  is  a  flattened, 
leaf-like  muscular  organ,  attached  to  the  symphysis  of  the  lower  jaw  in 
front,  and  to  the  os  hyoides  behind.  It  has  a  vertical  sheet  of  fibrous 
tissue  in  the  median  line  serving  as  its  framework,  and  is  provided  with 
longitudinal,  transverse,  and  radiating  muscular  fibres,  by  which  it  can 
be  protruded  or  retracted,  or  moved  in  a  lateral  direction. 

The  lingual  papillae  are  of  three  kinds.  First  the  filiform  papillae, 
which  are  the  most  numerous,  and  which  cover  most  uniformly  the 
upper  surface  of  the  tongue.  They  are  long  and  slender,  covered 
with  horny  epithelium,  and  usually  prolonged  into  filamentous  tufts. 
Secondly,  the  fungiform  papillae.  These  are  thicker  and  larger  than 
the  foregoing,  of  a  club-shaped  figure,  and  covered  with  soft  epithelium. 
They  are  most  abundant  at  the  tip  of  the  tongue,  but  may  be  seen 
elsewhere  on  the  surface  of  the  organ,  scattered  among  the  filiform 
papillae.  Thirdly,  the  circumvallate  papillae.  These  are  the  rounded 
eminences,  eight  or  ten  in  number,  which  form  the  V-shaped  figure  near 
the  foramen  caecum.  Each  consists  of  a  central  eminence,  surrounded 
by  a  wall  or  circumvallation,  from  which  they  derive  their  name.  The 
circumvallation,  as  well  as  the  central  eminence,  has  a  structure  similar 
to  that  of  the  fungiform  papilla}. 

The  sensitive  nerves  of  the  tongue  are  two  in  number,  namely,  the 
lingual  branch  of  the  fifth  pair,  and  the  lingual  portion  of  the  glos- 
sopharyngeal.  The  lingual  branch  of  the  fifth  pair  enters  the  tongue 
at  the  anterior  border  of  the  hyoglossal  muscle.  Its  branches  pass 
from  below  upward  and  from  behind  forward,  between  the  muscular 
bundles  of  the  organ,  until  they  reach  its  mucous  membrane,  where 
their  fibres  penetrate  the  lingual  papillae. 

The  lingual  portion  of  the  glossopharyngeal  nerve  passes  into  the 
tongue  below  the  posterior  border  of  the  hyoglossus  muscle.  It  then 
divides  into  branches,  which  pass  through  the  muscular  tissue,  and  are 
distributed  to  the  mucous  membrane  of  the  base  and  sides  of  the  organ. 

The  mucous  membrane  of  the  base  of  the  tongue,  of  its  edges,  and 
of  its  under  surface  near  the  tip,  as  well  as  that  of  the  mouth  and  famvs 
generally,  is  also  supplied  with  mucous  follicles  furnishing  a  viscid 
secretion  by  which  its  surface  is  lubricated.  The  muscles  of  the  tongue 
are  animated  exclusively  by  filaments  of  the  hypoglossal  nerve. 

The  ejuct  wat  of  the  SCUM-  of  ta>tr  lias  IHVII  determined  by  placing 


THE    SENSES.  515 

in  contact  with  different  parts  of  the  mucous  membrane  a  small  sponge, 
moistened  with  a  sweet  or  bitter  solution.  The  experiments  of  Duges, 
Verniere,  and  Longet,  have  shown  that  taste  resides  in  the  whole 
upper  surface,  the  point  and  edges  of  the  tongue,  the  soft  palate,  fauces, 
and  part  of  the  pharynx.  The  base,  tip,  and  edges  of  the  tongue  pos- 
sess the  greatest  amount  of  sensibility  to  savors,  the  middle  portion  of 
its  dorsum  less,  and  its  under  surface  little  or  none.  As  the  whole 
anterior  part  of  the  organ  is  supplied  by  the  lingual  branch  of  the  fifth 
pair,  and  the  whole  of  its  posterior  portion  by  the  glossopharyngeal, 
it  follows  that  the  sense  of  taste  is  derived  from  both  these  nerves. 

A  distinction  is  to  be  made,  in  the  action  of  foreign  substances  taken 
into  the  mouth,  between  the  special  impressions  derived  from  their 
sapid  qualities,  and  the  general  sensations  produced  by  their  ordinary 
physical  properties.  As  the  same  substance  is  often  capable  of  exciting 
both  tactile  and  gustatory  impressions,  they  are  sometimes  liable  to  be 
confounded  with  each  other.  The  qualities  which  we  perceive  by  the 
special  sense  of  taste  are  savors,  designated  by  the  terms  sweet,  bitter, 
salt,  sour,  alkaline,  and  the  like.  Beside  these,  however,  there  are 
other  qualities,  which  partake  largely  of  the  nature  of  ordinary  physical 
properties,  appreciable  by  means  of  general  sensibility.  A  starchy, 
oily,  or  mucilaginous  taste,  when  uncomplicated  with  additional  savors, 
is  but  little  different  in  kind  from  tactile  impressions.  The  quality  of 
pungency,  communicated  to  the  food  by  certain  condiments,  as  pepper 
or  mustard,  is  appreciated  altogether  by  the  general  sensibility.  The 
styptic  taste  seems  to  be  an  ordinary  astringent  effect  combined  with  a 
peculiar  excitement  of  the  gustatory  nerves,  analogous  to  that  caused 
by  the  galvanic  stimulus. 

Furthermore,  the  taste  or  savor  of  a  substance  is  to  be  distinguished 
from  its  odoriferous  properties  or  flavor.  In  most  aromatic  liquids, 
such  as  tea,  coffee,  and  wine,  a  great  part  of  the  effect  produced  is  due 
to  the  aroma  or  smell  which  reaches  the  posterior  nares  in  the  act 
of  swallowing.  Even  in  many  kinds  of  solid  food,  such  as  freshly 
cooked  meats,  odor  has  an  important  share  in  the  impression  on  the 
senses.  If,  during  the  deglutition  of  such  substances,  the  nares  be 
closed,  so  as  to  suspend  in  great  measure  the  sense  of  smell,  their  flavor 
becomes  nearly  imperceptible  ;  and  a  similar  effect  is  produced  by  catar- 
rhal  inflammation  of  the  nasal  passages,  which  impairs  for  the  time 
the  sensibility  of  the  olfactory  membrane. 

Necessary  Conditions  of  the  Sense  of  Taste. — There  are  certain  con- 
ditions requisite  for  gustatory  impressions,  beside  the  integrity  of  the 
organ  by  which  they  are  received. 

First,  the  sapid  substance,  in  order  that  its  taste  may  be  perceived> 
must  be  in  solution.  So  long  as  it  remains  solid,  however  marked  a 
savor  it  may  possess,  it  gives  no  other  impression  than  that  of  a  foreign 
body  in  contact  with  the  tongue.  But  if  applied  in  a  liquid  form,  it 
spreads  over  the  mucous  membrane,  and  its  taste  is  perceived.  Thus 
it  is  only  the  liquid  and  soluble  portions  of  the  food  which  are  tasted, 


THE     NERVOUS     SYSTEM. 

>uch  as  the  animal  and  vegetable  juices  and  tho  soluble  salts.  Saline 
>uhstanees  \vliirh  :nv  insoluble,  such  as  calomel  or  lead  carbonate,  pro- 
duce no  gustatory  impression. 

Tin-  mechanism  of  taste  is,  in  ;ill  probability,  direct  and  simple.  The 
sapid  substances  in  solution  are  absorbed  by  the  lingual  papillae,  and, 
coming  in  contact  with  the  terminal  nervous  filaments,  excite  sensibility 
byunitinjr  with  their  substance.  The  rapidity  with  which  endosmoHs 
will  take  place  under  certain  conditions  is  sufficient  to  account  for  the 
quick  perception  of  sapid  substances  introduced  into  the  mouth. 

It  is  on  this  account  that  free  secretion  of  saliva  is  favorable  to 
the  gustatory  function.-  If  the  mouth  be  dry,  food  has  but  little  taste. 
But  when  the  saliva  is  freely  secreted,  it  is  mixed  with  the  food  in 
mastication,  assisting  the  solution  of  its  sapid  ingredients;  and  the 
fluids  of  the  mouth,  impregnated  with  the  savory  substances,  are  ab- 
sorbed by  the  mucous  membrane  and  excite  the  gustatory  nerves. 

An  important  part  is  taken  in  this  process  by  the  movements  of  the 
tongue.  By  these  movements  the  food  is  carried  from  one  part  of 
the  mouth  to  another,  compressed  against  the  mucous  membrane,  its 
solution  assisted,  and  the  penetration  of  fluids  into  the  papilla?  more 
rapidly  accomplished.  If  powdered  sugar,  or  a  semi-solid  bitter  ex- 
tract, be  simply  placed  upon  the  dorsum  of  the  tongue,  little  or  no 
effect  is  produced ;  but  when  pressed  by  the  tongue  against  the  roof 
of  the  mouth,  in  the  movements  of  eating  or  drinking,  its  taste  is 
immediately  perceived.  This  is  explained  by  the  well-known  fact  that 
movement  and  friction  facilitate  the  liquefaction  and  imbibition  of 
soluble  substances.  The  nervous  papillae  of  the  tongue  may  therefore 
be  regarded  as  the  essential  instruments  of  taste,  and  the  lingual 
muscles  as  its  accessory  organs. 

Impressions  of  taste  made  upon  the  tongue  remain  for  a  certain 
time  afterward.  When  a  very  sweet  or  a  very  bitter  substance  is 
taken  into  the  mouth,  its  taste  is  retained  for  several  seconds  after  it 
has  been  ejected  or  swallowed.  Consequently,  if  different  savors  be 
presented  to  the  tongue  in  rapid  succession,  they  become  undistingui<h- 
able,  and  produce  only  a  confused  combination  of  several  impressions. 

If  the  substance  first  tasted  have  a  particularly  marked  savor,  its 
impression  will  preponderate  over  that  of  the  others.  A  similar  effect 
is  produced  by  substances  which  excite  the  general  sensibility  of  the 
tongue,  such  as  acrid  or  stimulating  powders;  and  it  belongs,  in  the 
greatest  degree,  to  substances  which  are  at  the  same  time  sapid,  pun- 
gent, and  aromatic,  like  sweetmeats  flavored  with  the  volatile  oils. 
Advantage  is  sometimes  taken  of  this  in  the  administration  of  disagree- 
able medicines.  By  first  taking  into  the  mouth  some  highly  flavored 
and  pungent  substance,  nauseous  drugs  may  be  immediately  swallowed 
with  but  little  perception  of  their  qualities. 


THE    SENSES. 


517 


FIG.  129. 


Sense  of  Smell. 

The  distinguishing  character  of  this  sense  is  that  it  appreciates  the 
quality  of  gaseous  or  vaporous  substances.  It  can  therefore  detect 
odoriferous  matters  at  a  distance,  and  when  concealed  from  sight.  It 
differs,  furthermore,  from  the  sense  of  taste  in  being  more  distinctly 
localized ;  since  it  is  confined  to  the  upper  portion  of  the  nasal  passages 
and  depends  on  the  filaments  of  a  single  pair  of  nerves. 

The  mucous  membrane  covering  the  superior  and  middle  turbinated 
bones  and  the  upper  part  of  the  septum  nasi,  which  is  alone  capable 
of  receiving  odorous  impressions,  is  known  as  the  olfactory  membrane. 
It  is  distinguishable  from  that  lining  the  rest  of  the  nasal  passages  : 
1st,  by  its  color,  which  in  man,  the  sheep,  and  the  calf  is  yellow,  but 
in  most  other  mammalia  has  a  brownish  tinge ;  2dly,  by  its  softer 
consistency ;  3dly,  in  the  greater  thickness  of  the  whole  membrane, 
and  especially  of  its  epithelial  layer.  According  to  Kolliker,  the  epi- 
thelium of  the  olfactory  membrane,  in  the  sheep  and  rabbit,  is  about 
sixty  per  cent,  thicker  than  that  of  the  remaining  nasal  membrane. 
In  most  quadrupeds  the  epithelium  of  the  nasal  mucous  membrane 
generally  is  covered  with  vibrating  cilia,  which  are  absent  in  the 
olfactory  portion ;  but  in  man  cilia  are  also  found  in  the  olfactory 
portion.  This  difference  is  probably  connected  with  the  inferior  acute- 
ness  of  smell  in  man,  as  compared 
with  the  lower  animals. 

The  nasal  passages  are  pro- 
vided with  nerves  from  three 
sources. 

I.  The  first  and  most  important 
of  these  are  the  olfactory  nerves 
(Fig.  129,  0.  They  are  derived 
from  the  olfactory  bulbs,  resting 
on  the  cribriform  plate  of  the 
ethmoid  bone,  through  which 
their  filaments  penetrate  the  up- 
per part  of  the  nasal  passages. 
They  contain  only  pale,  flattened, 
nucleated  nerve  fibres,  destitute 
of  a  medullary  layer.  Their 

branches    divide    and    subdivide,    DISTRIBUTION  OF  NERVES  IN  THE  NASAL  PAS- 
fbrming    microscopic    plexuses   in       «AGES.-I.  Olfactory  bulb,  with  its  nerves.    2. 

Nasal  branch  of  the  fifth  pair.    3.  Spheno-pala- 

the   substance   of    the    olfactory      tine  ganglion, 
membrane ;    and   the   finest  ner- 
vous ramifications  have  been  followed  nearly  to  the  epithelial  surface 
of  the  membrane. 

There  is  no  doubt  that  the  filaments  given  off  from  the  olfactory 
bulbs  are  the  special  agents  for  communicating  olfactory  impressions, 
and  that  they  are  the  only  ones  endowed  with  this  kind  of  sensibility. 


518  THE    NERVOUS    SYSTEM. 

So  far  as  we  can  judge  from  the  results  of  experiment,  they  are  not 
capable  of  receiving  or  transmitting  any  other  sensations  than  those 
excited  by  odoriferous  substances. 

II.  The  second  set  of  nerves  distributed  to  the  nasal  passages  con- 
si; sN  of  the  nasal  branch  of  the  fifth  pair,  and  its  ramifications  (Fig. 
129,2).     This  nerve,  after  entering  the  cavity  of  the  nose  a  little  in 
advance  of  the  cribriform   plate  of  the  ethmoid    bone,  is  distributed 
mainly  to  the  mucous  membrane  covering  the  inferior  turbinated  bone 
and  lining  the  inferior  meatus,  which  it  supplies  with  general  sensi- 
bility.   Some  of  its  filaments  are  also  continued  into  the  mucous  mem- 
brane of  the  olfactory  region,  in  proximity  with  those  of  the  olfactory 
nerves  ;  and  this  region,  according  to  the  observations  of  Babuchin,* 
possesses  consequently  a  certain  amount  of  general  sensibility,  though 
much  less  than  the  remainder  of  the  nasal  passages. 

III.  The  third  set  of  nerves  are  derived  from  the  spheno-palatine 
ganglion  of  the  sympathetic  (Fig.  129,  3),  which  supply  the  mucous 
membrane  of  the  posterior  part  of  the  nasal  passages  and  the  muscles 
of  the  posterior  nares.     Finally,  the  muscles  of  the  anterior  nares  are 
supplied  by  filaments  of  the  facial  nerve. 

Necessary  Conditions  of  the  Sense  of  Smell. — In  order  to  produce 
an  olfactory  impression,  the  emanations  of  the  odoriferous  body  must 
be  drawn  freely  through  the  nasal  passages.  As  the  olfactory  mem- 
brane is  situated  only  in  the  upper  part  of  these  passages,  whenever  a 
faint  or  delicate  odor  is  to  be  perceived,  the  air  is  forcibly  directed 
toward  the  superior  turbinated  bones,  by  a  peculiar  inspiratory  move- 
ment of  the  nostrils,  very  marked  in  many  of  the  lower  animals.  As 
the  odoriferous  vapors  arrive  in  the  upper  part  of  the  nasal  passages, 
they  are  probably  dissolved  in  the  secretions  of  the  olfactory  mem- 
brane, and  thus  brought  into  relation  with  its  nerves.  Inflammatory 
disorders  interfere  with  the  sense  of  smell,  both  by  altering  the  secre- 
tions of  the  part,  and  by  causing  tumefaction  of  the  mucous  membrane 
and  obstruction  of  the  nasal  passages. 

A  distinction  is  to  be  made  between  true  odors  and  the  excitement 
of  the  general  sensibility  of  the  nasal  membrane  by  irritating  sub- 
stances. Some  of  the  odors  arc  similar  in  their  nature  to  impressions 
of  taste.  Thus  there  are  sweet  and  sour  smells,  though  none  corre- 
sponding to  the  alkaline  or  the  bitter  tastes.  Most  odors,  however,  are 
of  a  peculiar  nature  and  difficult  to  describe ;  but  they  are  always  dis- 
tinct from  the  simply  irritating  properties  which  belong  to  certain 
vapors  and  gases.  Thus,  pure  alcohol  is  principally  a  stimulant  to  the 
mucous  membrane;  but  wines  have  in  addition  odoriferous  qualities, 
due  to  ingredients  of  vegetable  origin. 

The  vapor  of  pure  acetic  acid  is  simply  irritating  ;  while  vinegar  has 
also  a  peculiar  odor,  derived  from  its  vegetable  constituents.  Ammonia 
is  an  irritating  gas,  but  contains  no  proper  odoriferous  principle. 

tdur'fl  Manual  of  Histology,  Murk's  Edition.      NY\v  York,  1S742,  j>.  7JM). 


THE    SENSES.  519 

The  sense  of  smell,  which  is  only  moderately  developed  in  man,  is 
very  acute  in  many  animals.  The  dog  will  not  only  discover  game 
and  follow  it  by  the  scent,  but  will  distinguish  individuals  by  their 
odor,  or  recognize  articles  of  dress  belonging  to  them  by  the  minute 
quantity  of  odoriferous  vapor  adhering  to  the  fabric. 

Sense  of  Sight, 

This  is  the  most  remarkable  of  all  the  senses,  both  for  the  special 
nature  of  its  impressions,  the  complicated  structure  of  its  apparatus, 
and  the  variety  and  value  of  the  information  which  it  affords  with 
regard  to  external  objects.  It  is  by  this  sense  that  we  receive  impres- 
sions of  light  and  color,  with  all  their  modifications  of  intensity  and 
combination,  and  acquire  our  principal  ideas  of  form,  space,  and 
movement.  The  eye  is  equally  sensitive  to  the  impressions  of  light, 
whether  it  come  from  near  or  remote  objects,  or  even  from  the  immeas- 
urable distances  of  the  fixed  stars.  It  is  superior  to  the  other  organs 

FIG.  130. 


5 


HORIZONTAL  SECTION  OP  THE  EIGHT  EYEBALL.—!.  Optic  Nerve.  2.  Sclerotic  coat.  3.  Cornea.  4. 
Canal  of  Schlemm.  5.  Choroid  coat.  6.  Ciliary  muscle.  7.  Iris.  8.  Crystalline  lens.  9.  Retina. 
10.  Hyaloid  membrane.  11.  Canal  of  Petit.  12.  Vitreous  body. 

of  sense  in  its  rapidity  of  action,  and  in  the  delicacy  of  the  distinctions 
which  it  is  capable  of  making  in  the  physical  qualities  of  external  ob- 
jects ;  and  it  affords  the  most  continuous  and  indispensable  aid  for  all 
the  ordinary  occupations  of  life. 

Organ  of  Vision. — The  eyeball  consists  of  a  spheroidal  fibrous  sac, 
the  sclerotic  coat  (Fig.  130, 2),  filled  with  fluid  find  gelatinous  mate- 
rial, provided  anteriorly  with  a  transparent  portion,  the  cornea  G),  and 


520  THE    NERVOUS    SYSTEM. 

lined  posteriorly  with  a  nervous  expansion,  the  retina  (9),  which  is 
sensitive  to  light,  and  which  receives  the  luminous  rays  admitted 
through  the  cornea.  The  cavity  of  the  eyeball  is  therefore  like  that 
of  a  room  with  but  one  window,  where  all  the  light  enters  in  front, 
and  strikes  the  back  wall  of  the  apartment.  There  are,  in  addition  to 
the  above-mentioned  parts,  a  transparent  refracting  body  with  convex 
surface^,  the  crystalline  lens  (8),  by  which  the  light  is  concentrated  at 
the  retina ;  a  perforated  muscular  diaphragm,  the  iris  (7),  placed  in  front 
of  the  lens,  which  regulates  the  quantity  of  light  admitted  through  its 
central  orifice,  the  pupil;  and  finally  a  vascular  membrane  with  an 
opaque  layer  of  blackish-brown  pigment,  the  choroid  (5),  lining  the 
inner  surface  of  the  sclerotic  and  the  posterior  surface  of  the  iris,  thus 
preventing  reflections  within  the  eye,  and  absorbing  the  light  which 
has  once  passed  through  the  retina.  The  construction  of  the  eyeball, 
in  its  general  arrangement  as  an  organ  of  vision,  is  not  unlike  that  of 
a  photographic  camera;  where  the  sensitized  plate  at  the  back  part 
represents  the  retina,  the  blackened  inner  surface  of  the  box  the 
choroid,  while  the  optical  glasses  of  the  tube  in  front  perform  the 
office  of  the  crystalline  lens  and  cornea  of  the  eyeball. 

Sclerotic  Coat. — The  sclerotic,  so  named  from  its  toughness  and 
resistance,  is  the  external  protective  membrane  of  the  eyeball.  It  is 
composed  of  condensed  connective  tissue,  similar  to  that  of  the  fascia1 
and  fibrous  membranes  in  general;  and  toward  its  anterior  third  it 
receives  the  tendons  of  the  external  muscles  of  the  eyeball,  which 
become  fused  with  its  substance.  Posteriorly  it  is  continuous  with  the 
neurilemma  of  the  optic  nerve  (Fig.  130,  j),  which  penetrates  it  from 
behind  at  its  entrance  into  the  eyeball.  A  portion  of  the  sclerotic  is 
visible  anteriorly  through  the  conjunctiva,  forming  the  so-called  "  white" 
of  the  eye. 

Cornea. — The  cornea,  which  derives  its  name  from  its  horny  con- 
sistency and  appearance,  forms  the  anterior  part  of  the  wall  of  the  eye- 
ball. It  occupies  the  nearly  circular  space  left  at  this  situation  by  the 
deficiency  of  the  sclerotic,  with  which  it  is  continuous  at  its  edges ; 
the  difference  in  the  physical  appearance  of  the  two  being  that  the 
sclerotic  is  white  and  opaque,  while  the  cornea  is  colorless  and  trans- 
parent, so  that  the  colored  iris  and  dark  pupil  are  visible  through  its 
substance.  The  surface  of  the  cornea  has  a  sharper  curvature  than 
that  of  the  sclerotic,  and  projects  from  the  front  of  the  eyeball,  like 
a  small  dome  set  upon  a  larger  one.  Its  outline,  where  it  joins  the 
edge  of  the  sclerotic,  is  a  little  oval  in  form,  its  transverse  diameter 
being  slightly  longer  than  the  vertical.  At  its  centre,  it  is  about  0.8 
millimetre  in  thickne-s,  becoming  a  little  thicker  at  its  edges.  Its 
anterior  surface  is  kept  polished  and  brilliant  by  the  watery  lachrymal 
secretion,  distributed  over  it  by  the  movements  of  the  eyeball  and  lids. 

At  the  outer  border  of  the  cornea  tin-re  is  a  small  circular  canal,  the 
cti/nif  of  Sr/ili-inin  (  Fig-  I.'JO,  ,),  enclosed  in  this  part  of  the  wall  of 
the  eyeball.  The  posterior  wall  of  the  canal  of  Schlemm  is  composed 


THE    SENSES.  521 

of  elastic  and  tendinous  tissue,  and  gives  attachment  to  the  ciliary 
muscle  on  the  one  hand,  and  on  the  other  to  the  outer  border  of  the 
iris.  The  canal  is  regarded  by  most  anatomists  as  occupied  by  a 
venous  plexus,  receiving  veins  from  the  ciliary  muscle  and  from  the 
anterior  part  of  the  sclerotic. 

Choroid. — The  choroid  coat  is  a  vascular  and  pigmentary  mem- 
brane, lining  the  inner  surface  of  the  sclerotic,  and  presenting  ante- 
riorly a  thickened  portion,  the  "  ciliary  body."  The  inner  part  of  the 
ciliary  body  is  thrown  into  radiating  folds,  the  "  ciliary  processes," 
which  surround  the  borders  of  the  crystalline  lens.  The  inner  surface 
of  the  choroid  is  occupied  by  a  layer  of  hexagonal  nucleated  cells,  filled 
with  blackish-brown  pigment.  Similar  pigment  is  also  deposited, 
though  less  abundantly,  in  the  substance  and  near  the  external  sur- 
face of  the  choroid.  At  its  anterior  part,  the  choroid  is  separated  from 
the  sclerotic  by  the  ciliary  muscle  (Fig.  130,  6).  This  muscle  is  com- 
posed of  unstriped  fibres,  which  arise  from  the  posterior  wall  of  the 
canal  of  Schlemm,  at  the  junction  of  the  sclerotic  and  cornea,  and 
thence  diverge  in  a  radiating  direction,  outward  and  backward,  to  be 
inserted  into  the  external  surface  of  the  choroid,  where  it  passes  into 
the  folds  of  the  ciliary  processes.  At  the  anterior  and  inner  part  of  the 
muscle  there  are  also  bundles  of  circular  fibres,  parallel  with  the  margin 
of  the  cornea.  The  muscle  is  thus  composed  of  two  parts,  namely,  an 
internal  circular,  and  an  external  radiating  portion,  the  fibres  of  which 
are  more  or  less  interwoven  with  each  other  at  its  inner  edge. 

Iris. — The  iris  is  a  variously  colored  membrane,  extending  across 
the  cavity  of  the  eyeball,  attached  by  its  external  border  to  the  pos- 
terior wall  of  the  canal  of  Schlemm,  and  presenting  at  its  centre  the 
nearly  circular  orifice  of  the  pupil.  It  consists  of  connective  and  mus- 
cular tissue,  with  an  abundant  supply  of  blood-vessels,  and  is  covered 
on  its  posterior  surface  by  a  layer  of  blackish-brown  pigment  cells, 
continuous  with  those  of  the  choroid.  The  color  of  the  iris,  which 
appears,  in  different  individuals,  blue,  gray,  brown,  or  black,  depends 
on  the  abundance  and  disposition  of  its  pigmentary  elements.  In  gray 
and  blue  eyes,  the  visible  hue  of  the  iris  comes  from  the  diffused  light 
of  its  semi-transparent  tissues,  seen  against  the  dark  background 
of  the  pigment  layer  on  its  posterior  surface.  In  brown  and  black 
eyes,  the  pigment  is  more  abundant,  and  is  deposited,  according  to 
Kolliker  and  Cruveilhier,  not  only  on  the  posterior  aspect  of  the  iris, 
but  also  in  its  stroma,  between  its  fibres,  and  to  some  extent  even  on 
its  anterior  surface.  It  thus  predominates,  and  extinguishes  more  or 
less  completely  the  diffused  light  of  the  remaining  elements  of  the  tissue. 

The  position  of  the  iris  is  such  that  while  its  outer  border  is  attached 
to  the  junction  of  the  cornea  and  sclerotic,  its  central  portion  is  in  con- 
tact with  the  anterior  surface  of  the  crystalline  lens.  According  to 
Helmholtz,*  the  iris  in  myopic  eyes  is  sometimes  so  nearly  flat  that 
it  throws  no  perceptible  shadow  under  an  extreme  lateral  illumination  ; 
but  in  normal  eyes,  as  a  rule,  the  portion  immediately  surrounding  the 


522  TUP:  NERVOUS  SYSTEM. 

pupil  is  sufficiently  prominent  to  throw  a  distinct  shadow;  and  if  the 
source  of  illumination  be  not  more  than  one  millimetre  in  advance  of 
the  edge  of  the  cornea,  the  shadow  may  extend  even  to  its  opposite 
border. 

When  the  pupil  dilates,  the  central  prominence  of  the  iris  of  course 
diminishes,  or  disappears;  but,  according  to  Helmholtz,  the  pupillary 
border  of  the  iris  hardly  separates  from  the  anterior  face  of  the  lens, 
even  in  the  most  complete  dilatation  obtainable  by  belladonna. 

The  muscular  fibres  of  the  iris  are  arranged  in  two  sets,  namely,  the 
sphincter  and  dilator  muscles  of  the  pupil. 

The  sphincter  pupillae  is  composed  of  circular  fibres,  situated  at  the 
pupillary  margin  of  the  iris,  in  such  a  manner  that  their  contraction 
diminishes  the  orifice  of  the  pupil,  while  their  relaxation  allows  its 
enlargement.  When  the  sphincter  is  in  a  state  of  moderate  contrac- 
tion, the  remaining  non-contractile  tissues  are  thrown  into  radiating 
folds,  which  extend  from  the  pupillary  margin  for  one-third  or  one- 
half  the  distance  toward  the  outer  border  of  the  iris. 

The  dilator  pupillae,  which  consists  of  radiating  fibres,  is  more  dif- 
ficult of  demonstration,  and  its  existence  in  man  continued  to  be  a 
matter  of  uncertainty,  after  it  was  known  to  be  present  in  animals. 
It  has,  however,  been  described  by  so  many  independent  observers, 
that  there  can  be  no  doubt  of  its  forming  a  normal  part  of  the  muscu- 
lar apparatus  of  the  iris.  Its  fibres  are  interwoven  with  those  of  the 
sphincter  at  the  pupillary  margin,  and  thence  diverge  toward  the 
attached  border  of  the  iris,  either  as  isolated  bundles  running  between 
the  blood-vessels  (Briicke,  Kolliker),  or  as  a  very  thin,  continuous 
sheet  on  the  posterior  surface  of  the  iris,  beneath  its  pigmentary  layer 
(Henle,  Iwanoff ).  According  to  Kolliker,  the  iris  also  contains  ele- 
ments analogous  to  the  fibres  of  elastic  tissue,  which  may  assist  in  its 
dilatation. 

The  pigmentary  layer,  which  is  continuous,  over  the  inner  surface 
of  the  choroid,  the  ciliary  processes,  and  the  posterior  surface  of  the 
iris,  is  called  the  system  of  the  uvea,  from  its  resemblance  to  the  skin 
of  a  purple  grape  separated  from  its  stem,  the  opening  of  the  mem- 
branous sac  at  the  point  of  detachment  representing  the  orifice  of  the 
pupil.  Owing  to  the  existence  of  this  layer,  no  light  can  penetrate 
the  eyeball  except  through  the  pupil ;  and  rays  which  have  reached  the 
retina  at  any  point  are  arrested  there,  and  prevented  from  dispersion 
over  other  parts. 

Aqueous  Humor  and  Vitreous  Body. — The  cavity  of  the  eyeball  is 
divided,  by  the  transverse  partition  of  the  iris,  into  two  portions — an 
anterior  and  posterior.  The  portion  in  front  of  the  iris,  called  the 
"  anterior  chamber,"  is  filled  with  a  colorless,  transparent  watery  fluid, 
the  aqueous  humor.  This  fluid  serves  to  maintain  the  internal  tension 
of  the  eyeball,  and  to  allow  of  changes  in  the  iris  and  crystalline  lens, 


*  Optiqiu-  Physiolo^iqur.     I'uris,  1SU7,  p.  20. 


THE    SENSES.  523 

without  affecting  the  external  configuration  of  the  cornea.  The  pos- 
terior and  larger  portion  of  the  cavity  of  the  eyeball  is  filled  by  a  semi- 
fluid gelatinous  substance,  the  vitreous  body,  so  called  from  its  trans- 
parent and  glassy  appearance.  Its  refractive  power,  according  to 
Helmholtz,  though  slightly  greater  than  that  of  the  aqueous  humor, 
does  not  differ  much  from  that  of  water.  It  distends  the  greater  part 
of  the  cavity  of  the  sclerotic,  supports  the  retina  which  lies  upon  its 
surface,  and  preserves  the  spheroidal  form  of  the  eyeball. 

The  vitreous  body  is  enveloped  by  an  exceedingly  thin,  colorless 
membrane,  for  the  most  part  without  definite  structure,  and  according 
to  Kollikcr,  not  more  than  4  mmm.  in  thickness.  This  is  the  "  hyaloid 
membrane  "  (Fig.  130, 10).  It  extends  over  the  posterior  and  middle 
portions  of  the  vitreous  body  to  a  zone  corresponding  with  the  ciliary 
body  of  the  choroid.  Here  it  becomes  thicker  and  divides  into  two 
layers.  The  anterior  layer,  which  is  the  stronger  of  the  two,  the  zone 
of  Zinn,  extends  forward  and  inward,  remaining  adherent  to  the  ciliary 
body,  and  terminates  in  the  capsule  of  the  crystalline  lens,  just  in  front 
of  its  laternl  border.  The  posterior  layer  passes  inward  and  a  little 
backward,  terminating  also  in  the  capsule  of  the  lens,  but  a  little  behind 
its  lateral  border.  The  triangular  canal  between  the  two  layers  of  the 
hyaloid  membrane  and  the  lateral  border  of  the  lens  is  the  canal  of 
Petit  (Fig.  130,  n)>  and  is  filled  with  a  transparent  serosity.  The  lens 
is  thus  suspended,  from  all  sides,  by  a  double  layer  derived  from  the 
hyaloid  membrane. 

Crystalline  Lens. — The  lens  is  a  transparent,  refractive  body,  with 
convex  anterior  and  posterior  surfaces,  placed  directly  behind  the  pupil, 
where  it  is  retained  in  position  by  the  counterbalancing  pressure  of  the 
aqueous  humor  and  the  vitreous  body,  and  by  the  suspensory  layers  of 
the  hyaloid  membrane. 

As  its  refractive  power  is  greater  than  that  of  the  cornea  or  the 
aqueous  humor,  it  acts,  by  virtue  of  its  double-convex  form,  as  a  con- 
verging lens,  to  change  the  direction  of  rays  passing  through  it,  and 
bring  them  to  a  focus  behind  its  posterior  surface.  The  amount  of  con- 
vergence thus  effected  by  a  refractive  lens  depends  on  the  substance 
of  which  it  is  composed  and  the  curvature  of  its  surfaces.  The  stronger 
the  curvatures,  for  lenses  composed  of  the  same  material,  the  greater 
their  refractive  power  for  luminous  rays.  In  the  crystalline  lens  of  the 
human  eye,  the  two  surfaces  are  different  in  curvature ;  the  anterior 
being  comparatively  flat,  the  posterior  more  convex.  According  to  the 
estimates  of  Listing,  based  on  a  variety  of  measurements  and  adopted 
by  Helmholtz,  the  radius  of  curvature  for  the  anterior  surface  is,  on 
the  average,  10  millimetres,  that  for  the  posterior  surface  6  millimetres. 

This  makes  the  crystalline  lens  the  strongest  refracting  body  in  the 
eyeball,  and  by  its  aid  parallel  or  diverging  rays  are  brought  to  a  focus 
at  the  retina.  This  effect  is  not  due  entirely  to  the  lens,  since  the  con- 
vex form  of  the  cornea  and  the  more  or  less  spheroidal  figure  of  the 
whole  eyeball  have  in  some  degree  a  similar  action.  According  to 


524  THE    NERVOUS    SYSTEM. 

Helmholtz,  parallel  rays  would  l>e  brought  to  a  focus  by  the  cornea 
alone  at  a  point  10  millimetres  behind  the  retina.  But  on  passing 
through  the  lens,  their  convergence  is  increased  to  such  a  degree  that 
they  are  concentrated  at  the  retina. 

The  function  of  the  crystalline  lens  ?'x  In  <//»r  perception  of  form  and 
ntitliin'.  If  the  eye  consisted  only  of  a  sensitive  retina,  covered  with 
transparent  integument,  although  impressions  of  light  would  be  received 
\>\  such  a  retina,  they  could  give  no  idea  of  the  form  of  objects,  but 
only  the  sensation  of  a  confused  luminosity.  This  condition  is  illus- 
trated in  Fig.  l:jl.  where  the  arrow,  a,  6,  represents  the  luminous  object, 
and  the  vertical  dotted  line,  at  the  right  of  the  diagram,  represents  the 
retina.  The  rays  diverging  from  every  point  of  the  object  will  thus 
reach  every  part  of  the  retina  (1,  2,  3,  4,);  and  each  one  of  these  parts 
will  receive  rays  coming  both  from  the  point  of  the  arrow,  a,  and  from 
its  butt,  b.  There  will,  therefore,  be  no  distinction,  upon  the  retina, 
between  different  parts  of  the  object,  and  no  perception  of  its  figure. 
But  if,  between  the  object  and  the  retina,  there  be  inserted  a  lens,  with 
the  proper  curvatures  and  density,  as  in  Fig.  132,  the  effect  will  be  dif- 
ferent. All  the  rays  emanating  from  a  will  then  be  concentrated  at  x, 


VISION  WITHOUT  A  LENS.  VISION  WITH  A  LKNS. 

and  all  those  emanating  from  b  will  be  concentrated  at  y.  Thus  the 
retina  will  receive  the  impression  of  the  point  of  the  arrow  separate 
from  that  of  its  butt;  and  all  parts  of  the  object,  in  like  manner,  will 
be  distinctly  perceived. 

The  action  of  a  lens,  in  thus  focussing  luminous  rays  at  a  particular 
point,  may  be  illustrated  in  the  following  manner:  If  a  sheet  of  white 
paper  be  held  at  a  short  distance  from  a  candle  flame,  in  a  room  with  no 
other  source  of  light,  the  whole  of  the  paper  will  be  moderately  and 
uniformly  illuminated  by  the  diverging  rays.  But  if  a  double  convex 
•Has.-  lens,  with  suitable  curvatures,  be  interposed  between  the  paper 
and  the  light,  the  outer  portions  of  the  paper  will  become  darker  and 
its  central  portion  brighter,  because  a  portion  of  the  rays  are  diverted 
from  their  original  course  and  bent  inward.  By  varying  the  distance 
of  the  lens  from  the  paper,  a  point  will  at  last  be  found,  where  none  of 
the  light  reaches  the  external  parts  of  the  sheet,  hut  all  of  it  is  concen- 
trated upon  a  single  >pot  ;  and  at  this  spot  will  be  seen  a  distinct  image 
of  the  end  of  the  candle  and  its  flame. 

Percept  inn  of  the  figure  of  external  objects  therefore  depends  on  the 


THE    SENSES.  525 

action  of  the  crystalline  lens  in  converging  all  the  rays,  emanating  from 
a  given  point,  to  a  focus  at  the  retina.  For  this  purpose,  the  density 
of  the  lens,  the  curvature  of  its  surfaces,  and  its  distance  from  the  retina, 
must  all  be  properly  adapted  to  each  other.  If  the  lens  were  too  convex, 
and  its  refractive  power  excessive,  or  if  its  distance  from  the  retina 
were  too  great,  the  rays  would  cross  each  other  and  become  partially  dis- 
persed before  reaching  the  retina,  as  in  Fig.  133.  The  visual  impres- 
sion, therefore,  of  any  point  in  the  object,  would  not  be  concentrated 
and  distinct,  but  diifused  and  dim,  from  being  more  or  less  dispersed 
over  the  retina,  and  interfering  with  the  impressions  from  other  parts. 
On  the  other  hand,  if  the  lens  were  too  flat,  as  in  Fig.  134,  or  too  near 
the  retina,  the  rays  would  not  come  to  a  focus,  but  would  strike  the 
retina  separately,  producing  a  confused  image,  as  before.  In  both  cases, 
the  immediate  cause  of  the  confusion  of  sight  would  be  the  same, 
namely,  that  rays  from  each  point  of  the  object  are  dispersed  over 
the  retina ;  but  in  the  first  instance,  this  is  because  they  have  converged 
and  crossed  each  other ;  in  the  second,  it  is  because  they  have  only  ap- 
proximated, and  have  never  come  to  a  focus. 

FIG.  133.  FIG.  134. 


INDISTINCT  IMAGE  from  excessive  refractiuu.          INDISTINCT  IMAGE  from  deficient  refraction. 

The  proof  that  the  rays  are  thus  concentrated,  in  the  living  eye,  at 
the  retina,  is  furnished  by  the  ophthalmoscope.  This  instrument  con- 
sists of  a  mirror,  so  placed  as  to  illuminate  by  reflected  light,  through 
the  pupil,  the  bottom  of  the  eye  under  observation,  and  perforated  at 
its  centre  by  a  small  opening  through  which  the  observer  looks.  By 
this  means  the  retina  and  its  vessels,  as  well  as  the  images  delineated 
upon  it,  may  be  seen.  According  to  Helmholtz,  luminous  objects  at 
a  certain  distance,  when  distinctly  perceived  by  the  person  under  obser- 
vation, present  to  the  eye  of  the  observer  well-defined  inverted  images 
upon  the  retina.  Furthermore,  if,  from  the  eyeball  of  a  recently-killed 
animal,  a  circular  portion  of  the  sclerotic  and  choroid  be  removed  at 
its  posterior  part,  similar  inverted  images  of  objects  in  front  of  the 
cornea  may  be  seen  by  transparency  on  the  exposed  portion  of  the 
retina. 

It  is  accordingly  certain  that  divergent  luminous  rays,  in  passing 
through  the  eyeball,  are  brought  to  a  focus  at  the  retina,  principally  by 
means  of  the  crystalline  lens.  The  formation  of  a  visible  image  at 
this  spot  does  not  by  itself  explain  the  phenomena  of  vision,  since 


526  THE    NERVOUS    SYSTEM. 

these  images  are  not  seen  by  the  individual,  and  we  should  not  even 
know  of  their  existence  except  for  the  results  of  experiment  and  obser- 
vation. But  it  shows  that  all  the  light  coming  from  each  part  of  the 
object  is  made  to  fall  upon  a  single  point  of  the  retina ;  and  it  thus 
becomes  possible  to  perceive  the  figure  of  an  object,  as  well  as  its 
luminosity. 

Retina. — The  retina  is  the  most  essential  part  of  the  organ  of  vision, 
since  it  is  the  only  one  directly  sensitive  to  light.  It  forms  a  nearly 
transparent  membrane,  composed  of  nervous  elements,  situated  between 
the  inner  surface  of  the  choroid  and  the  outer  surface  of  the  hyaloid 
membrane,  and  extending  from  the  entrance  of  the  optic  nerve  to  the 
commencement  of  the  ciliary  body.  Here  it  terminates  by  an  indented 
border,  the  ora  serrata,  nearly  at  the  plane  of  the  posterior  surface  of 
the  crystalline  lens.  In  front  of  this  region  it  is  replaced  by  an  attenu- 
ated layer,  in  contact  with  the  surface  of  the  ciliary  body,  which  con- 
tains no  nervous  elements.  It  has,  accordingly,  the  form  of  a  mem- 
brane moulded  upon  a  nearly  hemispherical  surface,  with  its  concavity 
directed  forward,  and  receiving  the  rays  admitted  through  the  pupil. 
Its  greatest  thickness  is  in  the  immediate  vicinity  of  the  optic  nerve, 
where  it  measures,  according  to  Kolliker,  0.40  millimetre.  At  a  short 
distance  from  this  point  it  is  reduced  to  0.20,  and  thence  becomes  gradu- 
ally thinner  in  its  middle  and  anterior  portions.  At  the  ora  serrata, 
it  is  only  0.09  millimetre  in  thickness. 

The  retina  consists  of  superimposed  layers,  containing  many  different 
microscopic  elements.  In  regard  to  its  physiological  properties,  so  far 
as  they  have  been  determined,  four  of  these  layers  may  be  distinguished 
as  representing  its  essential  constituents.  These  layers,  counting  from 
the  inner  to  the  outer  surface  of  the  retina,  are  as  follows :  1.  The  layer 
of  nerve  fibres ;  2.  The  ganglionic  layer  of  nerve  cells ;  3.  The  layer 
of  nuclei ;  4.  The  layer  of  rods  and  cones. 

1.  Layer  of  Nerve  Fibres. — The  optic  nerve  joins  the  posterior  part 
of  the  eyeball  about  2  millimetres  inside  its  longitudinal  axis,  and  at  a 
slightly  lower  horizontal  plane.  Its  neurilemma  becomes  continuous 
with  the  sclerotic  coat,  while  its  nerve  fibres  penetrate  the  cavity  of 
the  eyeball.  Up  to  this  point  the  optic  nerve  consists  of  dark-bordered 
medullated  fibres,  having,  according  to  Kolliker,  a  diameter  of  from  1 
to  4.5  mmm.  But  at  their  entrance  into  the  eyeball  they  become  much 
smaller,  being  reduced,  on  the  average,  to  less  than  2  mmm.,  and  many 
of  them  to  less  than  1  mmm.  in  diameter.  Owing  to  these  changes, 
the  nerve  appears  suddenly  diminished  in  size  at  its  passage  through 
the  sclerotic.  Internally  it  forms  a  slight  prominence  at  the  fundus  of 
the  eye,  the  so-called  papilla;  and  the  central  artery  and  vein  of  the 
retina  emerire  at  this  point.  From  the  papilla  as  a  centre  the  optic 
nerve  fibres,  which  have  thus  reached  the  inner  surface  of  the  retina, 
radiate  laterally  in  every  direction  under  the  form  of  a  closely  set  layer. 
This  layer  diminishes  irradiially  in  thickness  from  the  centre  outward, 
owing  to  the  fact  that  its  fibres  terminate  siuvessively  in  the  deeper 


THE    SENSES. 


527 


FIG.  135. 


parts  of  the  membrane.     The  longest  fibres  continue  their  course  to 
the  ora  serrata,  beyond  which  none  are  visible. 

2.  Ganglionic  Layer  of  Nerve  Cells. — This  layer,  which  is  situated 
immediately  outside  the  former,  contains  multipolar  nerve  cells,  similar 
to  those  of  the  gray  substance  of  the  brain.     According  to  Kolliker, 
they  vary  in  size  from  9  to  36  mmm.  in  diameter,  and  are  provided 
with  pale,  ramified  prolongations.     Some  of  these  prolongations  are 
directed  toward  the  more  external  portions  of  the  retina ;  others  pass 
in  a  horizontal  direction,  and,  according  to  some  observers  (Kolliker, 
M tiller,  Corti),  become  continuous  with  optic  nerve  fibres. 

3.  Layer  of  Nuclei. — The  most  characteristic  elements  of  this  layer 
have,  in  the  main,  the  aspect  of  nuclei ;  although  by  some  observers  (Kol- 
liker, Schultze),  they  are  regarded  as  nucleated  cells,  in  which  the  envel- 
oping cell-substance  is  scanty,  as  compared  with  the  size  of  the  nucleus. 
The  nuclei,  sometimes  called  "grains  "  or  "granules,"  are  oval  bodies, 
with  their  long  axes  perpendicular  to  the  surface  of  the  retina.     They 
are  of  two  varieties,  differing  mainly  in  size ;  the  larger  being  from  9 
to  13  mmm.  in  length,  the  smaller  one-half  or  two-thirds  as  long. 
They  are  all  contained  in  varicose  enlargements  of  slender  fibres,  also 
directed  perpendicularly  to  the  surface  of 

the  retina,  and  extending  through  the  whole 
thickness  of  the  layer.  These  are  presumed 
to  be  of  the  nature  of  nerve  fibres,  and  to 
represent,  directly  or  indirectly,  the  continu- 
ations of  those  from  the  optic  nerve.  At 
their  outer  extremities  they  are  continuous 
with  the  elements  of  the  following  layer. 

4.  Layer  of  Rods  and  Cones. — This    is 
the  most  remarkable  of  the  retinal  layers, 
consisting  of  elements  more  peculiar  in  form 
than  those  found  elsewhere,  and  most  directly 
connected  with  the  physiology  of  luminous 
impressions.    As  their  name  indicates,  these 
elements   are   of  two   kinds,   namely,   the 
"rods"  and  the  "cones."     There  is  reason 
to  believe  that  they  are  modifications  of 
each  other,  and  that  their  offices  in  vision 
are  essentially  similar. 

The  rods  (Fig.  135)  are  straight,  elon- 
gated, cylindrical  bodies,  composed  of  a 
transparent,  homogeneous  substance,  re- 
markable for  its  highly  refractive  power. 

They  are  about  50  mmm.  in  length  by  a  lit-    DIAGRAMMATIC  SECTION,  from  the 
tie  less  than  2  mmm.  in  diameter.     They 
are  placed  parallel  with  each  other,  closely 
packed  side  by  side,  perpendicularly  to  the 
surface  of  the  retina.     At  its  outer  extremity  each  rod  terminates  by 


cones.     2.    Layer   of   nuclei. 


f)2.S  T  TT  K     X  K  R  VOU8     S  Y  S  T  K  M  . 

a  piano;  at  its  inner  extremity  it  tapers  to  a  jn»int  and  heroines  con- 
tinuous  with  a  fibre  of  the  preceding  layer.  According  to  Schult/e, 
the  inner  half  of  each  rod  is  slightly  thicker,  and  exhibits  rather  less 
refractive  power  than  the  outer  half. 

Tin-  cones  differ  from  the  rods  mainly  in  their  tapering  form  and  the 
"•renter  diameter  of  their  inner  portion,  which  is  generally  two  or  three 
times  as  thick  as  that  of  the  rods.  Their  extremities,  in  some  regions, 
stop  short  of  the  outer  surface  of  the  retina,  as  in  Fig.  135,  while  in 
that  of  most  perfect  vision  they  reach  the  same  level  with  the  rods. 
Karh  cone  is  connected  at  its  inner  extremity  with  a  nucleated  fibre  of 
the  preceding  layer,  the  only  peculiarity  in  this  respect  being  that  the 
fibres  and  nuclei  connected  with  the  cones  are  larger  than  those  con- 
nected with  the  rods. 

Over  the  greater  part  of  the  retina  the  rods  are  more  abundant  than 
the  cones.  When  viewed  from  the  outer  surface  (Fig.  136,  A),  their 
closely  packed  extremities  present  the  appearance  of  a  fine  mosaic,  while 
the  cones  are  interspersed  among  them  in  smaller  numbers.  At  the 
borders  of  the  macula  lutea,  the  cones  are  more  abundant,  being  only 
separated  from  each  other  by  single  ranges  of  rods  (5);  and  at  its 
central  portion  (  C)  there  are  only  cones,  the  rods  being  entirely  absent. 
But  the  cones  at  this  point  are  longer  and  more  slender  than  elsewhere. 
In  the  following  figure  the  smaller  circles  represent  the  rods,  the  larger 

circles  the  cones  ;  and  in  the  interior  of 
1  I(J-  136.  each  cone  is  seen  a  section  of  its  conical 

extremity. 

Reception  of  Luminous  Impressions 
by  the  Retina.  —  It  appears,  from  the 
above,  that  the  retina  is  not  simply  an 
expansion  of  the  optic  nerve.  It  is  an 

aPParatus  of  8Pecial  structure-  adaPted 

B.  From  the  edge  of  the  macula  lutea.  for  the  reception  of  luminous  rays,  and 
(Helm"  connected  by  the  optic  fibres  with  the 
central  parts  of  the  brain.  An  exami- 
nation of  the  manner  in  which  impressions  of  light  are  received  brings 
into  view  the  following  facts  : 

The  Optic  Nerve  and  its  Fibres  are  insensible  to  light.  —  Notwith- 
standing that  this  nerve  is  capable  of  transmitting  impressions  of  sight 
from  the  retina  to  the  brain,  yet  in  order  to  do  this,  it  must  first  receive 
its  own  stimulus  from  the  retina.  Its  fibres  cannot  be  called  into 
activity  by  the  direct  influence  of  luminous  rays.  This  is  shown  by 
the  experiment  of  Ponders,  in  which  a  light  of  some  intensity  is  con- 
centrated upon  the  optic  nerve,  without  being  allowed  to  reach  the 
tissue  of  the  retina.  When  the  bottom  of  the  eye  is  illuminated  by 
the  ophthalmoscope,  the  observer  >ees  the  general  surface  of  the  retina 
of  a  red  or  browni>h  color,  while  the  papilla,  at  the  entrance  of  I  lie 
optic  nerve,  presents  itself  as  a  circular  white  spot.  This  spot  is  occu- 
pied entirely  by  optic  nerve  fibres,  the  elements  of  the  retina  com- 


OUTKK  SI-RKACK  OF  THE  RETINA,  show- 


THE    SENSES.  529 

mencing  only  beyond  its  borders.  If  the  light  of  a  candle  flame  at 
some  distance  be  thrown  upon  the  retina,  it  is  perceived  by  the  person 
under  observation,  as  well  as  its  image  by  the  observer.  If  the  eye, 
however,  be  turned  in  such  a  direction  as  to  bring  the  image  of  the 
flame  upon  the  white  circle  of  the  papilla,  this  circle,  and  the  nerve 
fibres  of  which  it  is  composed,  are  visibly  illuminated  to  a  certain 
depth,  owing  to  the  translucency  of  their  substance ;  but  the  light  is 
no  longer  perceived  by  the  person  under  examination.  The  moment 
the  image  is  allowed  to  pass  beyond  the  limits  of  the  white  circle,  its 
light  becomes  perceptible. 

The  Blind  Spot. — The  region,  accordingly,  occupied  by  the  entrance 
of  the  optic  nerve,  from  which  the  proper  elements  of  the  retina  are 
absent,  is  a  blind  spot,  where  luminous  rays  make  no  perceptible  im- 
pression. The  diameter  of  this  spot,  according  to  the  average  measure- 
ments by  Listing,  Hannover,  and  Helmholtz,  is  1.65  millimetre,  and  it 
covers  in  the  field  of  vision  a  space  of  about  6  degrees.  Notwithstand- 
ing its  existence,  no  dark  point  is  usually  observed  in  the  field  of  vision, 
for  the  following  reasons :  The  blind  spot  is  not  situated  in  the  visual 
axis  of  the  eye,  but  corresponds  with  the  entrance  of  the  optic  nerve, 
nearer  the  median  line  (Fig.  130).  Consequently  the  image  of  an 
object  in  the  normal  line  of  vision  cannot  fall  upon  this  spot,  but  is 
always  outside  of  it,  in  the  visual  axis.  Even  an  object  perceived  out- 
side the  direct  line  of  sight  can  never  reach  the  blind  spot  of  both  eyes 
at  once.  If  so  placed,that  its  image  falls  on  the  blind  spot  of  one  eye, 
it  will  necessarily  reach  the  retina  of  the  other  eye  at  a  different  point, 
and  will  thus  be  perceived.  But  if  one  eye  alone  be  employed,  there 
is  always  a  small  portion  of  the  field  of  vision  which  is  imperceptible. 
This  deficiency  is  not  generally  noticed,  because  it  is  in  a  part  of  the 
field  to  which  our  attention  is  not  directed,  and  where  the  distinction 
of  objects,  under  moderate  illumination,  is  so  imperfect,  that  the  mo- 
mentary absence  of  one  is  not  regarded.  It  may,  however,  be  made 
apparent  by  using  for  the  test  a  single  strongly  defined  object,  like  a 
white  spot  on  a  black  ground,  the  presence  or  absence  of  which  may 
be  observable,  even  in  indirect  vision. 

If  the  left  eye  be  covered  and  the  right  eye  directed  steadily  at  the 
white  cross  in  Fig.  137,  the  circular  spot  will  also  be  visible,  though 
less  distinctly,  since  it  will  be  out  of  the  direct  line  of  sight.  Let  the 
page  be  held  vertically  at  the  height  of  the  eyes,  and  at  a  convenient 
distance  for  seeing  both  objects  in  the  above  manner.  If  it  be  now 
moved  slowly  backward  and  forward,  a  point  will  be  found  where  the 
circular  spot  disappears,  because  its  image  has  fallen  upon  the  blind 
spot ;  while  both  within  and  beyond  this  distance  it  is  again  visible. 
It  may  also  be  made  to  reappear  by  inclining  the  page  laterally  to  the 
right  or  left ;  since  this  brings  its  image  either  above  or  below  the 
blind  spot. 

The  experiment  may  be  varied  by  fixing  two  cards,  at  the  height  of 
the  eyes,  upon  a  dark  wall,  two  feet  apart  from  each  other.  If  the  left 

21 


530  THE   XEKVOUS  SYSTEM. 

eye  be  covered,  and  the  right  eye  fixed  upon  the  left-hand  card,  the 
other  will  disappear  from  view  at  a  distance  of  about  eight  feet  from 
the  wall. 

It  is  evident,  furthermore,  that  the  optic  nerve  fibres  are  not  directly 
sensitive  to  light,  even  outside  the  blind  spot.  These  fibres  radiate 
from  the  entrance  of  the  optic  nerve,  forming  a  continuous  sheet  on 
the  inner  surface  of  the  retina;  terminating  at  successive  points  in 
the  retinal  membrane  to  its  extreme  border.  A  luminous  ray  striking 
the  retina  near  the  fundus  of  the  eye  must,  therefore,  traverse  a  con- 
siderable number  of  nerve  fibres,  connected  at  their  peripheral  extremi- 
ties with  different  parts  of  the  retina ;  and,  though  coming  from  a  sin- 
gle point,  it  would  thus  cause  the  sensation  of  an  extended  line.  As 

FIG.  137. 


DIAGRAM,  for  observing  the  situation  of  the  blind  spot.    (Helmholtz.) 

distinct  points  are  separately  perceived,  although  the  rays  emanating 
from  each  have  passed  through  the  whole  layer  of  nerve  fibres  in  the 
retina,  it  follows  that  these  fibres  are  not  directly  affected  by  the  action 
of  light. 

The  sensitive  elements  of  the  retina  are  in  its  posterior  or  external 
Layers. — This  is  apparent  partly  from  the  phenomena  observed  when 
the  retinal  blood-vessels  are  made  visible  within  the  eye.  These  vessels 
and  their  branches  radiate  from  the  entrance  of  the  optic  nerve.  Their 
ramifications,  down  to  a  certain  size,  are  situated  in  the  innermost  layer 
of  the  retina,  and  it  is  only  the  finest  subdivisions  which  pass  into 
the  layer  of  ganglionic  cells.  The  two  outer  layers,  namely,  that  of 
the  nuclei,  and  that  of  the  rods  and  cones,  are  destitute  of  blood-vessels. 
Owing  to  this  arrangement,  the  outer  layers  of  the  retina,  situated 
behind  the  main  branches  of  the  blood-vessels,  lie  in  the  shadow  of 
these  branches,  since  the  light  comes  directly  from  the  front  through 
the  pupil.  The  shadows  thus  thrown  are  not  usually  perceived,  because 
the  portions  of  retina  covered  by  them  are  hnbitunlly  in  shadow  at  the 
same  points,  and  their  sensibility  to  light  is  greater  in  proportion.  But 
they  may  be  rendered  perceptible  by  throwing  them,  under  oblique 
illumination,  upon  un accustomed  points  of  the  retina. 

Let  u  lighted  randle  he  held,  in  a  dark  room,  about  three  inches  from 


THE    SENSES.  531 

the  outer  angle  of  the  eye,  and  about  45  degrees  in  front  of  the  plane 
of  the  iris.  On  moving  the  candle  alternately  up  and  down,  the  field 
of  vision  becomes  filled  with  an  abundant  tracery  of  arborescent  figures, 
the  counterpart  of  the  retinal  blood-vessels.  The  form  of  the  vessels 
is  marked  in  purple-black,  on  a  finely  granular  grayish-red  ground. 
The  point  of  entrance  of  the  vascular  trunks  may  be  seen,  with  their 
two  principal  branches  passing  respectively  upward  and  downward, 
and  breaking  into  ramifications  of  various  curvilinear  form.  If  the 
candle  be  held  motionless,  the  figures  rapidly  fade,  since  they  are 
only  visible  from  the  contrasts  made  by  the  shadows  falling  in 
succession  on  different  parts  of  the  retina. 

As  the  blood-vessels  of  the  retina  are  situated  nearly  at  its  anterior 
surface,  the  motion  of  their  shadows,  perceptible  on  varying  the  posi- 
tion of  the  light,  gives  a  means  of  ascertaining  how  far  behind  this 
surface  the  sensitive  elements  are  situated.  According  to  Miiller,*  this 
distance  must  be,  in  various  cases,  from  0.17  to  0.36  millimetre;  and 
the  same  observer  finds  the  posterior  layers  of  the  retina  distant  from 
its  anterior  surface  from  0.20  to  0.30  millimetre.  It  is,  therefore,  one 
or  both  of  the  posterior  layers,  namely,  the  rods  and  cones,  and  the 
nuclei  immediately  beneath,  in  which  luminous  rays  produce  their 
effect. 

Macula  Lutea  and  Point  of  Distinct  Vision. — The  macula  lutea,  or 
yellow  spot  of  the  retina,  is  an  oval  space,  about  2  millimetres  in  trans- 
verse diameter,  between  2  and  2.5  millimetres  outside  the  entrance  of 
the  optic  nerve.  According  to  Helmholtz,  it  is  placed  a  very  little 
beyond  the  middle  of  the  fundus  of  the  eyeball,  toward  its  temporal 
side.  It  is  distinguished  from  the  remainder  of  the  retina  by  its  yellow 
tinge,  due  to  the  presence  of  an  organic  pigment. 

At  its  centre  is  a  minute  depression,  the  fovea  centralis,  where,  owing 
to  its  steeply  sloping  sides,  the  thickness  of  the  retina  is  reduced,  at  its 
deepest  part,  to  less  than  one-half.  Its  position  in  the  macula  lutea,  in 
ophthalmoscopic  examinations,  is  marked  by  a  peculiar  colorless  reflec- 
tion. The  macula  lutea,  and  especially  the  fovea  centralis,  is  the  point 
of  most  distinct  vision,  where  the  image  of  an  object,  in  the  direct  line 
of  sight,  falls  upon  the  retina.  According  to  the  observations  of  Bon- 
ders, confirmed  by  Helmholtz,  if,  while  the  retina  is  illuminated  by  the 
ophthalmoscope,  the  person  under  observation  fixes  the  eye  upon  sev- 
eral different  objects  in  succession,  the  minute  reflection  which  marks 
the  fovea  centralis  always  places  itself  upon  the  optical  image  of  the 
object  fixed  by  the  eye ;  and  this  appearance  is  so  constant  that  the 
observer  can  tell  with  certainty,  from  the  place  occupied  by  the  reflec- 
tion, at  what  object  the  sight  is  directed. 

The  importance  of  the  macula  lutea  and  fovea  centralis,  in  the  exer- 
cise of  vision,  gives  a  special  interest  to  the  anatomy  of  this  part  of 
the  retina ;  and  microscopic  researches  have  shown  that  it  presents 

*In  Helmholtz,  Optique  Physiologique.    Paris,  1867,  p.  289. 


532 


THE    NERVOUS    SYSTEM 


peculiarities  of  structure  corresponding  with  its  physiological  endow- 
ments. 

The  macula  lutea  is  distinguished,  in  the  first  place,  by  the  absence 
of  the  layer  of  nerve  fibres.  Those  fibres,  according  to  Kolliker, 
which,  in  radiating  from  the  entrance  of  the  optic  nerve,  reach  the 
edges  of  the  macula,  lose  themselves  among  the  nerve  cells  of  its 
ganglionic  layer.  The  others  curve  round  its  borders  on  each  side, 
and  resume  their  peripheral  course  beyond ;  so  that  there  are  none 
to  be  found  within  the  limits  of  the  yellow  spot. 

Secondly,  the  nerve  cells  of  the  ganglionic  layer  are  more  abundant 
in  the  macula  lutea  than  elsewhere.  Over  the  greater  portion  of  the 
retina,  according  to  Schultze,  these  cells  are  arranged  in  a  single  plane ; 


FIG.  138. 


DIAGRAMMATIC  SECTION  OF  HUMAN  RETINA,  through  the  macula  lutea  and  fovea  centralis.— 1. 
Inner  surface  of  the  retina.  2.  Ganglionic  layer  of  nerve  cells.  3.  Intermediate  layers  of  the 
rctiiia,  disappearing  at  the  centre  of  the  macula  lutea.  4.  Layer  of  nuclei,  showing  the  oblique 
course  of  its  fibres  in  this  region.  5.  Layer  of  rods  and  cones;  consisting  at  its  central  portion 
exclusively  of  attenuated  and  elongated  cones.  6.  Outer  surface  of  the  retina.  The  depression 
in  the  middle  of  the  diagram  is  the  fovea  ceutralis.  (Schultze.) 

but  in  the  yellow  spot  they  form  several  superimposed  ranges.  Toward 
the  centre  of  the  yellow  spot,  on  the  other  hand,  they  diminish  in  num- 
ber, and  are  entirely  wanting  at  the  fovea  centralis. 

Thirdly,  owing  to  these  modifications,  the  retina,  at  the  fovea  cen- 
tralis, consists  only  of  its  two  external  layers,  namely,  the  layer  of  nuclei 
and  the  layer  of  rods  and  cones.  Even  these  layers  exhibit,  at  the 
same  point,  important  peculiarities  in  the  form  and  arrangement  of  their 
elements. 

In  the  layer  of  nuclei,  the  fibres  with  which  they  are  connected,  instead 
of  remaining  perpendicular  to  the  surface  of  the  retina,  bend  obliquely 
outward,  to  reach  its  more  superficial  parts  in  the  outer  portions,  or 
beyond  the  borders,  of  the  yellow  spot.  Thus  the  layer  is  much 
diminished  in  thickness,  though  still  containing  nuclei,  connected,  by 
tln-ir  usual  extensions,  with  other  parts  of  the  retina. 

Finally,  the  layer  of  rods  and  cones,  at  the  macula  lutea  and  fovea, 
is  distinguished  by  special  features  from  the  corresponding  parts  else- 
where. At  this  situation  it  is  increased  in  thickness,  and  consists 
exclusively  of  slender  elongated  cones.  The  diameter  of  the  cones  at 


THE    SENSES.  533 

their  base  is  reduced  from  6  mmm.  to  3  or  3.5  mmm. ;  while  their  length 
reaches  100  mmm.,  or  about  double  what  it  is  elsewhere.  Each  cone  is 
connected,  through  the  nucleus  and  fibre  of  the  preceding  layer,  with 
other  portions  of  the  retina,  and,  no  doubt,  in  some  way,  with  the  nerve 
fibres  of  its  inner  layer. 

Thus,  the  perception  of  light  is  a  process  consisting  of  several  suc- 
cessive acts.  The  luminous  ray  passes  through  the  tissue  of  the  retina, 
until  it  reaches  the  layer  of  rods  and  cones.  In  these  elements  it  pro- 
duces a  reaction  of  whose  nature  we  are  ignorant.  It  might  be  com- 
pared with  that  caused  by  the  same  agent  in  the  sensitive  film  of  a 
photographic  camera;  but  this  comparison  would  be  only  one  of  analogy, 
and  would  not  imply  any  identity  of  molecular  action  in  the  two  cases. 
It  would  simply  express  the  fact,  which  is  undoubtedly  established, 
that  the  luminous  ray,  after  traversing  all  the  other  transparent  and 
refracting  media  of  the  eye  without  leaving  any  trace  of  its  passage, 
on  arriving  at  the  outer  layers  of  the  retina,  excites  in  them  a  change 
of  condition  which  is  the  first  step  in  the  visual  process.  The  excite- 
ment of  the  retina  then  calls  into  activity  the  fibres  of  the  optic  nerve, 
which  in  turn  transmit  the  stimulus  to  their  origin  at  the  base  of  the 
brain.  Thus  far,  there  is  no  conscious  perception,  nor  even  any  nervous 
effect  resembling  our  idea  of  luminosity.  The  retina  is  distinguished 
from  other  nervous  tissues  by  being  sensitive  to  light ;  that  is,  it  may 
be  thrown  into  a  state  of  activity  under  the  influence  of  a  luminous  ray. 
But  it  has  no  proper  perception  of  light,  any  more  than  the  silvered 
film  of  a  photographic  plate ;  and,  if  the  optic  nerve  be  severed,  blind- 
ness results,  however  perfect  the  condition  of  the  retina. 

On  the  other  hand,  the  optic  nerve  fibres,  which  are  insensible  to  the 
direct  action  of  light,  are  thrown  into  excitement  by  the  condition  of 
the  retinal  tissue.  There  is  no  reason  for  believing  that  the  optic 
fibres  are  different  in  kind  from  those  of  other  sensitive  nerves.  Their 
office  is  simply  that  of  transmitting  a  stimulus  from  and  to  certain 
special  structures  containing  nerve  cells.  By  the  optic  nerve  fibres 
the  stimulus  is  received  from  the  retina  and  communicated  to  the  brain ; 
and  the  nervous  centres,  when  thus  excited,  first  produce  the  sensation 
and  perception  of  light. 

Acuteness  of  Vision  in  the  Retina. — The  acuteness  of  vision,  in  the 
retina,  is  measured  by  the  distance  between  two  visual  rays  at  which 
they  can  be  perceived  as  distinct  points.  If  the  rays,  coming  respec- 
tively from  the  top  and  bottom  of  an  object,  are  so  closely  approxi- 
mated at  the  retina  that  the  two  impressions  are  confounded,  there  can 
be  no  distinct  perception  of  its  figure  or  dimensions.  On  the  other 
hand,  if  the  sensibility  of  the  retina  be  such  that  the  two  impressions 
are  separately  perceived,  the  form  of  the  object  will  be  recognized  as 
well  as  its  luminosity,  notwithstanding  the  small  size  of  its  retinal 
image.  The  figure  of  a  man,  six  feet  high,  seen  at  a  distance  of  ten 
yards,  makes  at  the  cornea  a  visual  angle  of  11°  30',  and  forms  upon 
the  retina  an  image  less  than  half  a  millimetre  (-£$  of  an  inch)  in  length  ; 


THE    NERVOUS     SYSTEM. 

and  yet  an  abundance  of  details  an-  distinctly  perceptible  within  this 
space.  The  extreme  limit  of  approximation  at  which  two  points  may 
be  distinguished  from  each  other  has  l>ccn  examined  by  the  observation 
of  fixed  stars,  and  by  that  of  parallel  threads  of  the  spider's  web,  or  of 
fine  wires,  placed  at  known  distances  from  each  other.*  These  exami- 
nations show  that,  for  average  well-formed  eyes,  the  smallest  visual 
angle,  at  which  adjacent  points  can  be  distinguished,  is  from  GO  to  73 
seconds ;  corresponding  to  a  distance  upon  the  retina  of  from  4  to  5 
mmm.  According  to  Schultze,  the  diameter  of  the  retinal  cones,  at  the 
fovea  centralis,  is  from  3  to  3.5  mmm. ;  and  if  two  beams  of  light  were 
separated  at  the  retina  by  a  less  distance  than  this,  they  might  fall 
upon  the  same  cone,  and  consequently  excite  the  same  connecting  fibre 
in  the  adjacent  layer.  If  the  diameter  of  the  cones  be  the  element 
which  determines  the  acuteness  of  vision,  two  luminous  points,  to  be 
distinctly  perceptible,  must  be  separated  upon  the  retina  by  a  distance 
of  at  least  3  mmm.,  and  must  have  a  visual  angle  with  each  other  of 
at  least  42  seconds.  In  astronomical  observations,  it  is  found  that  two 
stars  can  never  be  separately  distinguished  by  the  eye,  unless  their 
angular  distance  from  each  other  is  equal  to  30  seconds;  and  very 
seldom,  unless  it  be  as  great  as  60  seconds.  These  measurements  are 
hardly  sufficient  to  decide  the  question ;  since  there  has  never  been  an 
opportunity  of  examining  the  size  of  the  retinal  elements  in  an  eye,  of 
which  the  acuteness  of  vision  had  been  previously  tested.  But  they 
are  enough  to  indicate  a  probable  connection  between  the  minute 
structure  of  the  retina  and  the  limit  of  its  sensibility  to  separate  im- 
pressions. 

The  Retinal  Red  and  its  alteration  by  light. — The  retina,  as  usually 
extracted  from  the  eye  of  a  recently  killed  animal,  is  colorless  or  slightly 
opaline.  But  in  its  normal  condition  in  the  living  eye,  or  if  extracted 
without  exposure  to  light,  it  is  of  a  purple-red  hue,  due  to  a  transparent 
coloring  matter  in  its  external  or  posterior  layer.  This  color,  the  so- 
called  "retinal  red,"  first  discovered  by  Boll,f  has  been  more  fully 
investigated  by  Kiihne.J  It  is  seated  exclusively  in  the  rods. of  the 
retina,  and  is  consequently  most  distinctly  marked  where  these  ele- 
ments are  most  abundant.  The  cones,  on  the  other  hand,  are  color- 
less. At  the  macula  lutea,  accordingly,  where  the  cones  preponderate 
over  the  rods,  the  reddish  tint  disappears ;  and  it  is  entirely  absent  at 
the  fovea  centralis,  where  the  membrane  consists  only  of  cones  and 
their  appendages.  Elsewhere,  it  extends  over  the  retina  to  within 
three  or  four  millimetres  of  the  ora  serrata,  where  it  terminates  by  a 
tolerably  well-defined  limit. 


*  Hehnholtz,  Optique  Physiologique.     Paris,  1867,  p.  292. 
f  Monatsberichte  der  kdnigliche    I'riMissisclu-n    Akademie   tier 
.Jahro  1X70.     Berlin,  1877,  P.  7 

J  UnUTsurliun^rn  aus  dcin    IMi  ysiulnuischen  lustitiiti-.      I  lenlt-lln-r^,  1X77.      IK-ft 
1,  -,  6. 


THE    SENSES.  535 

The  most  striking  character  of  the  retinal  red  is  that  it  is  destroyed 
by  the  action  of  light.  On  this  account  its  existence  remained  long 
unknown.  When  the  retina  is  extracted  from  the  eye  of  an  animal 
in  the  ordinary  way,  its  exposure  during  the  necessary  manipulations 
is  usually  sufficient  to  bleach  its  color  and  reduce  it  to  the  condition 
of  a  grayish  or  opalescent  membrane.  In  order  to  obtain  it  with  its 
normal  hue,  the  animal  should  be  kept  in  the  dark  for  a  short  time 
previous  to  death ;  and  the  eyeball  taken  out  and  the  retina  extracted 
by  the  light  of  a  sodium  flame,  which  has  comparatively  little  effect 
upon  its  color.  If  such  a  retina  be  exposed  to  bright  daylight  its  pur- 
ple-red tint,  at  first  distinctly  visible,  is  destroyed,  according  to  Ku'hne, 
in  about  half  a  minute.  Under  a  dim  daylight  it  lasts  longer,  and  by 
ordinary  gaslight  may  continue  visible  for  20  or  30  minutes ;  while  in 
a  chamber  lighted  by  the  sodium  flame,  or  in  the  dark,  it  remains  for 
24  or  48  hours,  even  after  the  tissues  have  lost  their  freshness  and  con- 
sistency. 

By  this  means  the  existence  of  the  retinal  red  has  been  demonstrated 
in  the  rabbit,  dog,  ox,  ape,  and  badger,  in  the  owl  and  falcon,  in  the  frog, 
triton,  toad,  and  salamander,  and  in  several  species  of  fish.  In  three 
instances  Ku'hne  found  it  in  the  human  eye,  extirpated  in  the  dark  or 
in  a  sodium-lighted  chamber,  from  subjects  who  had  been  protected 
from  the  light  for  a  certain  time  before  death. 

The  retinal  red  is  also  destroyed  by  the  action  of  light  during  life. 
This  is  not  usually  observable  in  an  eye  extracted  with  the  above- 
mentioned  precautions,  for  the  reason  that  during  life  the  color  is 
regenerated  nearly  as  fast  as  it  is  destroyed.  Thus  a  living  eye,  under 
moderate  illumination,  maintains  the  normal  hue  of  its  retina  by  the 
constant  reproduction  of  its  coloring  matter.  But  if  long  exposed  to 
light  of  considerable  intensity  it  may  become  completely  bleached, 
though  its  color  will  be  restored  by  repose  in  a  darkened  place.  Ku'hne 
found  that  in  frogs  exposed  to  daylight,  in  a  glass  vessel  with  a  white 
bottom,  the  retina  becomes  bleached  after  several  hours ;  and  that  in 
direct  sunshine  15  minutes  are  sufficient  to  produce  thq  same  effect.  But 
if  the  animals  be  then  kept  in  the  dark,  and  examined  at  various  inter- 
vals, the  color  of  the  retina  again  begins  to  be  perceptible  in  about  30 
minutes,  and  is  completely  restored  at  the  end  of  an  hour  and  a  half. 

The  source  from  which  the  color  is  thus  reproduced  is  the  choroidal 
epithelium,  with  which  the  retina  lies  in  contact.  If  separated  from 
its  attachment  and  exposed  to  daylight,  its  color  disappears,  as  already 
shown,  in  from  30  seconds  to  several  minutes.  But  if  allowed  to 
remain  in  the  eyeball  under  a  similar  exposure,  and  then  extracted 
under  the  light  of  a  sodium  flame,  on  bringing  it  into  ordinary  day- 
light it  is  at  first  of  a  deep  red.  In  Kuhne's  experiments,  a  portion 
of  a  frog's  retina,  separated  from  the  choroid  in  daylight  until  quite 
bleached,  then  replaced  and  allowed  to  remain  in  position  in  the  dark 
for  a  short  time,  exhibited,  when  finally  removed,  its  normal  red  color. 
It  is  accordingly  evident  that  the  regeneration  of  the  color  does  not 


r.:;r,  Tin-:   NKIIYOTS   SYSTEM. 

depend  on  the  circulating  blood,  since  it  will  take  place  in  the  extir- 
pated eyeball ;  but  is  affected  by  the  aid  of  tho  choroidal  epithelium. 

The  coloring  matter  of  the  retina  is  soluble  in  purified  bile,  or  in 
watery  solutions  of  the  biliary  salts,  and  has  been  extracted  by  Kiilnie 
in  this  way  under  the  form  of  a  transparent  solution.  The  frcshly- 
exiracted  frog's  retina  is  macerated  from  one  to  two  hours  in  one 
cubic  centimetre  of  a  five  per  cent,  watery  solution  of  the  biliary  salts. 
It  is  then  replaced,  in  the  same  solution,  by  another  retina,  also  freshly 
prepared  ;  and  so  on  until  20  or  30  retinas  have  been  employed  for  the 
purpose.  The  mixture  is  then  filtered  and  the  filtrate  allowed  to  stand 
until  the  pigment  granules  mingled  with  it  have  subsided  to  the  bot- 
tom, after  which  the  supernatant  liquid  is  removed  by  a  pipette.  It 
forms  a  clear  solution  of  a  carmine-red  color.  By  concentration  it 
assumes  a  more  violet  tinge,  and  if  diluted  becomes  rose-red  or  pale 
lilac,  according  to  the  amount  of  dilution. 

Solutions  of  the  retinal  red  are  bleached  by  light,  in  the  same  man- 
ner as  the  retina  itself.  Their  color  changes,  under  these  circumstances, 
first  to  a  clear  red,  then  becoming  orange,  then  yellowish,  and  lastly 
they  are  entirely  decolorized.  Similar  changes  are  effected  in  the  dark 
by  an  elevated  temperature;  beginning  at  50°  or  52°  C.,  becoming 
more  rapid  as  the  temperature  rises,  and  taking  place  almost  instan- 
taneously from  70°  to  74°  G. 

The  local  bleaching  of  the  retina  under  concentrated  illumination 
makes  it  possible  to  obtain  retinal  optograms,  that  is,  colorless  images 
of  brilliant  objects  which  have  been  placed  before  the  eye,  surrounded 
by  the  purple-red  hue  of  the  remaining  retina.  The  first  result  of  this 
kind  was  obtained  by  Ku'hne  in  the  following  manner :  The  fresh  retina 
of  a  rabbit,  extracted  under  the  light  of  a  sodium  flame,  was  spread  out 
on  a  glass  plate  and  secured  by  a  thin  cover-glass  on  which  were  sev- 
eral strips  of  tinfoil,  each  about  one  millimetre  in  width.  In  this  con- 
dition it  was  exposed  to  light  until  the  bleaching  process  was  complete ; 
and  on  removing  the  cover-glass,  bands  of  unchanged  purple-red  were 
visible  in  the  retina,  wherever  it  had  been  protected  by  the  tinfoil.  As 
the  form  of  any  luminous  object  in  front  of  the  eye  is  concentrated 
upon  a  single  part  of  the  retina,  this  part  will  be  bleached,  if  the 
exposure  be  sufficient,  while  the  remaining  portions  retain  their  color, 
thus  presenting  a  positive  image  of  the  luminous  object.  The  method 
adopted  by  Ku'hne  for  obtaining  optograms  in  the  rabbit's  or  ox's  eye 
follows :  The  eyeball  is  taken  out  in  a  dark  chamber  with  the  aid 
of  the  sodium  flame,  and  fixed,  with  the  cornea  upward,  in  a  blackened 
box  or  cylinder,  the  cover  of  which  is  removable.  The  box  containing 
the  eyeball  is  then  placed  upon  a  table  directly  beneath  an  illuminated 
skylight  of  ground  u  lass,  at  about  four  metres'  vertical  distance,  and  t  he 
cover  removed.  After  an  exposure  of  from  one  to  twenty  minutes, 
according  to  the  intensity  of  the  daylight,  the  opaque  cover  is  replaced, 
the  eyeball  opened  in  the  dark  chamber  by  an  equatorial  incision,  its 
posterior  half  freed  from  the  vitreous  humor,  and  placed  for  twenty- 


THE    SENSES.  537 

four  hours  in  a  four  per  cent,  watery  solution  of  potassium-alum.  The 
last  operation  is  for  the  purpose  of  giving  to  the  retina  a  greater  con- 
sistency, so  that  it  may  be  removed  from  the  eyeball  without  lacera- 
tion. When  the  hardening  is  complete  the  retina  is  removed,  and  placed, 
with  its  posterior  surface  uppermost,  upon  a  porcelain  capsule  of  suit- 
able convexity ;  when  the  images  of  the  window-panes  are  seen  in 
white,  with  the  intervening  bars  and  the  surrounding  spaces  purple- 
red.  On  exposure  to  daylight  the  images  disappear,  owing  to  the 
bleaching  of  the  whole  retina ;  but  if,  while  still  in  the  dark  chamber, 
it  be  thoroughly  desiccated,  its  color  becomes  comparatively  indestruc- 
tible, and  the  optograms  remain  visible  in  daylight  for  many  hours. 

Notwithstanding  the  evident  importance  of  the  retinal  red,  and  its 
sensibility  to  the  influence  of  light,  it  is  not  immediately  essential  to 
the  act  of  vision.  This  is  manifest,  in  the  first  place,  from  the  fact 
that,  in  the  human  eye,  it  is  absent  from  the  macula  lutea  and  fovea 
centralis ;  that  is,  from  the  spot  of  greatest  retinal  sensibility  and  most 
distinct  vision.  Ku'hne  has  furthermore  demonstrated  that  frogs  whose 
retinas  have  been  completely  bleached  by  continued  exposure  to  direct 
sunshine  are  still  capable  of  vision.  Under  these  circumstances  the 
retinal  red  is  regenerated,  even  in  the  dark,  somewhat  slowly,  and 
does  not  begin  to  show  itself  under  half  an  hour  (page  535).  During 
this  period,  therefore,  the  animals  have  no  appreciable  red  in  the  retinal 
tissue ;  and  yet  they  quickly  distinguish  moving  objects,  and  can  even 
capture  flies  in  their  usual  manner  with  readiness  and  precision.  They 
also  show  a  capacity  for  distinguishing  colors,  and  in  both  these  par- 
ticulars exhibit  a  marked  contrast  with  frogs  wh^ch  have  been  blinded 
by  extirpation  of  the  eyeballs. 

It  is  accordingly  quite  uncertain  in  what  way  the  coloring  matter 
of  the  retina  is  subservient  to  sight.  It  may  be  supposed  that  by  its 
transformation  under  the  influence  of  light  it  supplies  some  material 
for  the  continued  nutrition  of  the  nervous  elements;  and  that  this 
secondary  material  is  in  turn  consumed  during  the  act  of  vision.  But 
so  far  as  our  present  knowledge  extends,  there  is  no  satisfactory  evi- 
dence in  regard  to  its  mode  of  action. 

Physiological  Conditions  of  the  Sense  of  Sight. — The  eye,  so  far  as 
regards  its  physical  structure,  is  an  optical  instrument,  composed  of 
transparent  and  refracting  media,  a  perforated  diaphragm,  and  a  dark 
chamber,  all  of  which  act  upon  luminous  rays  according  to  the  same 
laws  as  the  corresponding  parts  in  a  telescope  or  a  camera ;  and  the 
accuracy  of  their  adjustment  is  one  of  the  first  requisites  for  the  exer- 
cise of  sight.  The  eye  is  also  movable  in  various  directions ;  and  cer- 
tain of  its  internal  parts  are  under  the  control  of  muscular  tissues, 
which  contribute  to  its  action.  It  is  furthermore  a  double  organ  ;  and 
impressions  may  be  acquired  by  the  use  of  both  eyes  which  cannot 
be  received  from  one  alone.  Finally,  the  sensibility  of  its  nervous  ele- 
ments is  lia,ble  to  modifications,  which  influence  the  nature  and  intensity 


538  THE    NERVOUS    SYSTEM. 

of  the  sensations  produced.  The  principal  conditions  regulating  the 
sense  of  sight  are  the  following  : 

Field  of  Vision. — As  the  eyeball  is  placed  in  the  orbit  with  the 
cornea  and  pupil  directed  forward,  there  is,  in  front  of  each  eye,  a  cir- 
cular space  within  which  objects  are  perceptible  ;  while  beyond  its  bor- 
ders nothing  can  be  seen.  This  space  is  the  "  field  of  vision."  Its 
extreme  limit,  in  man,  reaches  nearly  180  degrees  of  angular  distance; 
that  is  to  say,  the  light  from  a  brilliant  object  may  be  perceived,  when 
the  object  is  in  a  lateral  position,  almost  as  far  back  as  the  plane  of  the 
iris.  The  possibility  for  a  ray  of  light  from  this  source,  to  penetrate  the 
pupil  and  reach  the  retina,  depends  on  the  refractive  power  of  the  cornea 
and  the  curvature  of  its  anterior  surface,  by  which  the  ray  is  bent 
inward  and  enabled  to  enter  the  pupil  in  an  oblique  direction.  In  many 
animals,  where  the  eyes  are  more  prominent  than  in  man,  and  the  curva- 
tures of  the  cornea  and  crystalline  lens  more  pronounced,  the  field  of 
vision  is  enlarged  in  a  corresponding  degree.  In  birds  and  fishes,  it  is 
still  further  modified  by  the  lateral  position  of  the  eyes.  The  ostrich, 
with  the  head  directed  forward,  can  easily  see  objects  a  few  yards 
behind  its  back ;  and  in  many  fish,  when  examined  from  different  points 
in  an  aquarium,  it  is  impossible  for  the  observer  to  place  himself  in  any 
position,  above,  behind,  or  on  either  side,  where  he  cannot  see  one  or 
both  of  the  pupils  of  the  animal.  The  field  of  vision  consequently, 
for  such  animals,  is  a  complete  sphere  ;  the  light  being  perceptible  from 
every  point  of  the  surrounding  space.  In  man,  the  outer  borders  of 
the  field  of  vision  are  ill  defined ;  and  objects  at  a  lateral  distance  of  90 
degrees  must  be  very  brilliant  to  attract  attention.  For  practical  pur- 
poses, the  space  within  which  objects  are  perceptible  is  not  more  than 
75  degrees  on  each  side,  or  ]  50  degrees  for  the  entire  field  of  vision. 

Line  of  Direct  Vision. — Within  the  field  of  vision  there  is  only  one 
point,  at  its  centre,  where  objects  can  be  perceived  with  distinctness ; 
and  the  prolongation  of  this  point,  in  the  visual  axis,  is  called  the  "  line 
of  direct  vision."  Objects  upon  this  line  can  be  distinctly  seen ;  all 
others,  situated  on  either  side,  above  or  below  it,  are  perceived  only 
in  an  imperfect  manner.  If  the  observer  place  himself  in  front  of  a 
row  of  vertical  stakes,  he  can  see  those  directly  before  the  eye  with 
perfect  distinctness :  but  those  on  either  side  appear  as  uncertain  and 
confused  images.  On  looking  at  the  middle  of  a  printed  page,  in  the 
line  of  direct  vision,  we  see  the  distinct  outlines  of  the  letters ;  while 
at  successive  distances  from  this  point,  the  eye  remaining  fixed,  we 
distinguish  first  only  the  separate  letters  with  confused  outlines,  then 
only  the  words,  and  lastly  only  the  lines  and  spaces. 

This  limitation  of  serviceable  sight  to  the  line  of  direct  vision  is 
compensated  by  the  mobility  of  the  eyeball,  which  turns  successively 
in  different  directions;  thus  shifting  the  field  of  vision  and  examining 
in  turn  every  point  attainable  by  the  eye.  In  reading  a  printed  page, 
the  eye  follows  the  lines  from  left  to  right,  seeing  each  letter  and  word 


THE    SENSES.  539 

in  succession.  At  the  end  of  a  line,  it  returns  suddenly  to  the  next, 
repeating  this  movement  from  the  top  to  the  bottom  of  the  page. 

The  deficiency  of  distinctness  outside  the  line  of  direct  vision  depends 
on  two  causes,  both  of  which  contribute  to  the  result,  namely :  1st, 
inaccurate  focussing  of  the  rays  ;  and  2d,  diminished  retinal  sensibility. 

Rays  of  light  entering  the  eye  from  the  front,  in  the  line  of  direct 
vision,  are  brought  to  a  focus  at  the  retina.  But  those  which  enter 
with  a  certain  degree  of  obliquity  suffer  more  rapid  convergence,  and 
are  accordingly  brought  to  a  focus  and  again  dispersed  before  reaching 
the  retina.  Thus  rays  diverging  from  the  point  a  (Fig.  139),  in  the 
line  of  direct  vision,  are  concentrated  at  x,  and  form  a  distinct  image 
on  the  retina  at  that  point.  But  those  coming  from  b,  on  one  side, 
under  a  similar  degree  of  divergence,  fall  upon  the  cornea  and  the 
crystalline  lens  in  such  a  way  that  there  is  more  difference  in  their 
angles  of  incidence,  and  consequently  more  difference  in  the  amount  of 
their  refraction.  They  are  therefore  brought  together  too  rapidly,  and 
are  dispersed  at  the  retina  over  the  space  y,  z,  forming  an  imperfect 
image.  Ophthalmoscopic  examination  of  the  retina  shows  that,  in 
point  of  fact,  images  formed  at  the  fundus  of  the  eye,  in  the  line  of 
direct  vision,  present  distinct  outlines ;  while  those  at  a  distance  from 
this  point,  toward  the  lateral  parts  of  the  retina,  are  comparatively  ill- 
defined. 

Secondly,  the  sensibility  of  the  retina  is  less  acute  in  its  lateral 
regions  than  at  the  fundus  and  the  macula  lutea ;  since  according  to 
Helmholtz,  the  sharpness  of  sight  for  objects  at  a  distance  from  the  line 
of  direct  vision  diminishes  more  rapidly  than  the  distinctness  of  their 
images  on  the  retina.  Objects  in  the  visual  axis  are  seen  by  direct 
vision,  and  are  distinctly  perceived ;  those  situated  within  the  field  of 
view,  but  outside  this  axis,  are  seen  by  indirect  vision,  and  appear 
more  or  less  confused  in  outline. 

Point  of  distinct  vision,  and  Accommodation  for  different  distances. 
—An  optical  instrument,  composed  of  refracting  lenses,  cannot  be  made 
to  serve  at  the  same  time  for  near  and  remote  objects.  If  a  refracting 
telescope  or  spy-glass  be  directed  toward  any  part  of  the  landscape, 
only  the  objects  at  a  certain  distance  are  distinctly  seen ;  those  within  or 
beyond  this  distance,  are  obscure  or  imperceptible.  This  is  because  a 
system  of  lenses  can  bring  to  a  focus  at  one  point  only  those  rays  which 
strike  its  surface  within  a  certain  degree  of  divergence.  The  formation 
of  a  visible  image  at  the  desired  spot  depends  on  the  refracting  power 
of  the  lenses  being  such,  that  all  rays  diverging  from  the  object  shall 
be  brought  to  a  focus  at  the  plane  where  its  image  is  to  be  perceived. 
If  the  object  be  at  an  indefinite  distance  on  the  horizon,  or  if  it  be  one 
of  the  heavenly  bodies,  the  rays  from  any  point  of  its  surface  reach 
the  telescope  under  so  slight  a  degree  of  divergence  that  they  are  nearly 
parallel ;  and,  on  suffering  refraction,  they  will  be  brought  to  a  focus  a 
short  distance  behind  the  lens.  But  rays  emanating  from  an  object 
less  remote,  strike  the  lens  under  a  higher  degree  of  divergence.  The 


540  THE    NERVOUS    SYSTEM. 

same  refractive  power,  therefore,  brings  them  together  less  rapidly 
than  before,  and  they  come  to  a  focus  at  a  greater  distance  behind  the 
lens.  To  provide  for  this,  the  spy-glass  is  furnished  with  a  sliding 
tube,  l.y  which  the  distance  of  the  eye-piece  from  the  object-glass  may 
be  shifted  at  will.  For  examination  of  remote  objects,  the  eye-piece  is 
pushed  forward,  to  bring  into  view  the  image  formed  a  short  distance 
behind  the  lens;  for  that  of  near  objects  it  is  drawn  backward,  to  receive 
the  image  placed  farther  to  the  rear.  This  is  the  accommodation  of  the 
spy -glass  for  vision  at  different  distances. 

There  is  a  similar  necessity  in  the  eye.  If  one  eye  be  covered,  and 
two  vertical  needles  be  placed  in  front  of  the  other,  in  nearly  the  same 
linear  range,  but  at  different  distances — one,  for  example,  at  eight,  and 
the  other  at  twenty  inches  from  the  eye — it  will  be  found  that  they 

FIG.  139. 


DIAGRAMMATIC  SECTION  OF  THE  EYEBALL,  showing  difference  of  refraction  for  direct  and  indirect 
vision. — a,  x.  Rays  from  a  point  in  the  line  of  direct  vision,  focussed  at  the  retina,  b,  y,  z.  Rays 
from  a  point  outside  the  line  of  direct  vision,  brought  to  a  focus  and  dispersed  before  reaching 
the  retina. 

cannot  both  be  seen  distinctly  at  the  same  time.  When  we  look  at 
the  one  nearer  the  eye,  so  as  to  perceive  its  form  distinctly,  the  image 
of  the  more  remote  one  is  confused ;  and  when  we  see  the  more  dis- 
tant object  in  perfection,  that  which  is  nearer  loses  its  sharpness  of 
outline. 

The  same  thing  may  be  shown  by  stretching  in  front  of  the  eye,  at 
the  distance  of  seven  or  eight  inches,  a  gauze  veil,  or  other  woven 
fabric  of  fine  threads,  with  tolerably  open  meshes,  so  that  objects  may 
be  visible  through  its  tissue.  The  observer,  in  using  a  single  eye,  may 
fix  at  will  either  the  threads  of  the  veil,  or  the  objects  beyond  it ;  but 
they  alternate  with  each  other  in  distinctness,  like  the  two  needles  in 
the  foregoing  experiment.  When  the  threads  are  sharply  defined,  every- 
thinjr  <-Ise  is  indistinct;  and  when  the  eye  is  fixed  on  the  more  distant 
objects,  so  that  they  are  sharply  delineated  ill  the  field  uf  vision,  the 


THE    SENSES.  541 

threads  of  the  veil  become  almost  imperceptible,  and  hardly  interfere 
with  the  images  beyond. 

It  is  evident,  therefore,  that  the  eye  cannot  perceive  distinctly,  at 
the  same  time,  objects  at  different  distances,  but  it  must  fix  alternately 
the  nearer  and  the  more  remote,  and  examine  each  in  turn.  It  is  also 
evident  that,  in  thus  shifting  the  sight  from  one  object  to  the  other, 
there  is  some  change  in  the  condition  of  the  eye,  by  which  it  adapts 
itself  to  the  distance  of  the  object  examined ;  and  the  alteration  thus 
produced  is  not  quite  instantaneous,  but  requires  a  certain  time  for  its 
completion.  This  process  is  the  accommodation  of  the  eye  for  vision 
at  different  distances. 

The  method  by  which  this  is  effected  is  an  important  part  of  the 
physiology  of  sight.  Its  principal  conditions,  so  far  as  they  have  been 
ascertained,  are  the  following : 

I.  Accommodation  for  different  distances  is   accompanied  by  a 
change  in  distinctness  of  the  images  upon  the  retina. 

This  is  demonstrated  by  the  observations  of  Helmholtz  with  the 
ophthalmoscope.  When  the  retina  is  brought  into  view  by  this  in- 
strument, if  the  person  under  examination  fix  his  attention  upon  a 
distant  object,  its  image  appears  upon  the  retina  with  distinct  outlines ; 
but  on  changing  his  point  of  vision  to  a  near  object,  the  latter  image 
becomes  distinct,  while  the  former  loses  its  sharpness.  This  indicates 
that  the  result  is  not  produced  simply  by  mental  effort,  but  depends  on 
a  change  in  the  refractive  condition  of  the  eye. 

II.  Accommodation  for  distant  objects  is  a  passive  condition;  that 
for  near  objects  is  caused  by  muscular  activity. 

This  is  in  some  degree  apparent  from  the  accompanying  sensation. 
The  eye  rests  without  fatigue  for  an  indefinite  time  upon  remote  objects ; 
but  examination  of  those  in  close  proximity,  especially  if  prolonged, 
requires  a  certain  effort,  which,  after  a  time,  amounts  to  fatigue.  So- 
lutions of  atropine,  which,  when  applied  to  the  eye,  cause  relaxation  of 
the  sphincter  of  the  iris  and  dilatation  of  the  pupil,  suspend  at  the 
same  time  the  power  of  accommodation  for  near  objects,  while  that 
for  remote  objects  remains  perfect.  Furthermore,  in  certain  cases  of 
paralysis  of  the  oculomotorius  nerve,  not  only  the  external  muscles 
of  the  eyeball  and  the  sphincter  pupillae  are  relaxed,  but  accommoda- 
tion is  also  interfered  with ;  and  in  these  instances,  according  to  Helm- 
holtz, the  eye  remains  adapted  for  long  distances. 

III.  In  accommodation  for  near  objects,  the  crystalline  lens  becomes 
more  convex,  thus  increasing  its  refractive  power.     This  is  the  change 
upon  which  accommodation  is  directly  dependent.     It  was  first  demon- 
strated by  Cramer  and  Bonders,*  by  the  aid  of  "  catoptric  images,"  or 
images  of  reflection  in  the  eye.     If  a  candle  flame  be  so  disposed,  in  a 
room  with  dark  walls,  that  its  rays  fall  somewhat  obliquely  upon  the 
cornea,  and  at  an  angle  of  about  30  degrees  with  the  line  of  sight, 


*  DONPEES,  Accommodation  and  Refraction  of  the  Eye.     London,  1864,  p.  10. 


r>42 


THE     NERVOUS    SYSTEM. 


FK;.  140. 


and  if  the  observer  place  himself  on  the  opposite  side,  at  an  equal  angle 
with  the  line  of  sight,  three  reflected  images  of  the  flame  will  become 
\  i-iMe,  as  in  Fig.  140. 

The  first  image  (<i  ,  which  is  the  brightest,  and  upright,  is  reflected 
from   the   cornea.     The  second  (b),  which  is  also  upright,  but   much 
fainter,  is  from  the  convex  anterior  surface  of  the  lens ;  and  the  third 
(c),   which  is  tolerably  distinct,  but  inverted,   is 
from  the  posterior  surface  of  the  lens,  acting  as  a 
concave  mirror.     If  the  person  under  observation 
now  change  his  point  of  sight,  from  a  distant  to  a 
near  object,  the  eyeball  remaining  fixed,  the  second 
image  (6)  becomes  smaller,  and  places  itself  nearer 
the  first.    This  indicates  that  the  anterior  surface 
of  the  lens  becomes  more  prominent,  and  approaches 
the  cornea ;  but  there  is  no  change  in  the  other  two 
CATOPTRIC    IMAGES   IN    images,  showing  that  the  curvatures  of  the  cornea 
^mlge^fre^tio^from    and  Posterior  surface  of  the  lens  remain  unaltered, 
the  cornea,  b.  Upright        Helinholtz  has  made  these  phenomena  more  ap- 
parent by  employing,  instead  of  a  single  light,  two 
sources  of  illumination  in  the  same  vertical  line 
(Fig.  141).     This  gives  two  catoptric  images,  one 
above  the  other,  for   each  surface  of  reflection ; 
and  a  change  in  convexity  of  either  one  would  be  manifested  by  the 
approach  or  separation  of  its  images.     In  accommodation  for  remote 
objects  (^4),  the  images  from  the  anterior  surface  of  the  lens  are  rather 

large  and  widely  separated ;  in 
accommodation  for  near  objects 
(.B),  they  diminish  in  size  and 
approach  each  other.  The  reflec- 
tiong  from  the  cornea  and  those 
from  the  posterior  surface  of  the 
lens  remain  at  the  same  distance 
in  both  states  of  accommodation. 

The  advance  of  the  iris  and 
pupil,  from  protrusion  of  the  an- 
terior face  of  the  lens,  in  accom- 
modation for  near  objects,  can  be 


c.  Inverted  image,  from 
the  posterior  surface  of 
tin-  li-ns.  (Ht-lmholtz.) 


FIG.  141. 


a       6 


CHANOK  OP  POSITION  IN  DOUBLE  CATOPTRIC 
IMAGES  during  accommodation.— A.  Position 
of  the  images  in  accommodation  for  distant 
objects.  B.  Position  of  the  images  in  accom- 


VUjwW«  ni,i^«  •     in    iu:i  iiijj-  -  _  _  _  _ 

modation  for  near  objects,    a.  Corneal  image.     Observed,    as    remarked    by   llellll- 

';•  Imaf  fr ^'-<-i"r  surface  of  lens.    c.    holtz,  by  looking  into  the  eve  iron i 

I  ma,-,   from  posterior  surface  of  lens.    (Helm-  .  ,<7  J 

hi.it/.)  the  side.     The  person  under-   OM 

>ervation  fixes  his  sight  upon  a 

distant  object,  and  the  observer  places  himself  in  such  a  position  that 
the  edge  of  the  iris  is  just  concealed  by  the  sclerotic.  If  the  sight  be 
now  shifted  from  the  distant  object  to  a  nearer  one  in  the  same  linear 
ranire,  the  pupil  visibly  advances  toward  the  cornea,  and  the  iris  shows 
itself  a  little  in  front  of  its  former  position.  If  the  sight  IK-  again 


THE    SENSES.  543 

directed  to  the  distant  object,  the  pupil  recedes  and  the  edge  of  the  iris 
disappears  behind  the  sclerotic. 

The  accommodation  of  the  eye  for  near  objects  is  therefore  produced 
by  increased  refractive  power  of  the  lens,  from  the  greater  bulging 
of  its  anterior  face.  This  increases  the  convergence  of  rays  passing 
through  it,  and  compensates  for  their  greater  divergence  beforehand. 
In  the  condition  of  ocular  repose,  with  the  eye  directed  to  distant 
objects,  rays  coming  from  any  one  point  arrive  at  the  cornea  nearly 
parallel,  and  are  so  refracted  as  to  meet  in  a  focus  at  the  retina.  When 
the  eye  is  directed  to  a  nearer  point,  the  lens  increases  its  anterior  con- 
vexity ;  and  the  divergent  rays,  being  more  strongly  refracted,  are  still 
brought  to  a  focus  at  the  retina,  as  before.  It  thus  becomes  possible  to 
fix  alternately,  in  distinct  vision,  objects  at  various  distances. 

Mechanism  of  Accommodation. — The  means  by  which  the  lens  is 
rendered  more  convex,  in  vision  for  near  objects,  is  not  fully  demon- 
strated. Reasons  have  already  been  given  for  the  belief  that  it  is 
accomplished,  in  some  way,  by  muscular  action ;  and  the  two  muscles 
which,  separately  or  together,  undoubtedly  produce  this  change,  are 
the  iris  and  the  ciliary  muscle. 

The  pupil  certainly  contracts  in  accommodation  for  near  objects. 
This  is  easily  observed  on  examining  by  daylight  an  eye  which  is 
alternately  directed  to  near  and  remote  objects.  The  ciliary  muscle,  on 
the  other  hand,  cannot  be  inspected  in  this  way ;  but  its  attachments 
and  position  have  led  many  writers  to  consider  it  as  the  principal 
agent  in  changing  the  form  of  the  lens. 

It  appears  that  the  diminution  in  size  of  the  pupil  is  not  by  itself  an 
efficient  cause  of  accommodation ;  since,  according  to  Helmholtz,  if  the 
observer  look  through  a  perforated  card,  the  orifice  of  which  is  smaller 
than  the  pupil,  near  objects  still  appear  indistinct  when  the  sight  is 
directed  to  the  distance,  and  vice  versa,  notwithstanding  the  invariable 
dimensions  of  the  artificial  pupil  employed.  The  contraction  of  the 
sphincter  pupillae  probably  serves  to  fix  the  inner  border  of  the  iris, 
as  a  point  of  attachment  for  its  radiating  fibres.  These  fibres  are 
attached  externally  to  the  elastic  tissue  at  the  posterior  wall  of  the 
canal  of  Schlemm  (Fig.  130);  and  from  this  circle  also  arise  the 
fibres  of  the  ciliary  muscle,  which  radiate  thence  to  their  attachment 
at  the  choroid  membrane.  If  the  circular  and  radiating  fibres  of 
both  muscles  contract  together,  they  will  form  a  connected  system, 
which  may  exert  a  pressure  on  the  borders  of  the  lens,  sufficient  to 
cause  the  protrusion  of  its  anterior  face.  The  details  of  this  mechan- 
ism are  by  no  means  clearly  understood ;  and  explanations,  varying 
more  or  less  from  the  above,  have  been  proposed  by  observers  of  high 
authority.  The  direction  and  degree  in  which  pressure  would  be  exerted, 
by  muscular  fibres  attached  like  those  in  the  interior  of  the  eye,  are  too 
imperfectly  known  to  warrant  a  positive  statement  in  this  respect. 

Limits  of  Accommodation  for  the  Normal  Eye. — The  normal  eye  is 
so  constructed  that  rays  emanating  from  a  single  point,  though  coming 


54:4  THE    NERVOUS    SYSTEM. 

from  an  indefinite  distance,  and  therefore  sensibly  parallel,  are  brought 
to  a  focus  at  the  retina  (Fig.  142).  Vision  is  accordingly  distinct,  even 
for  the  heavenly  bodies,  provided  their  light  be  neither  too  dim  nor  too 
brilliant.  For  objects  situated  nearer  the  eye,  the  convexity  of  the  lens 
increases  with  the  diminution  of  distance,  and  vision  remains  perfect. 
But  there  is  a  limit  to  the  change  in  shape,  of  which  the  lens  is  capa- 
ble ;  and  when  this  limit  is  reached,  a  closer  approximation  of  the 
object  destroys  the  accuracy  of  its  image.  For  ordinary  normal 
eyes,  in  the  early  or  middle  periods  of  life,  accommodation  fails  and 
vision  becomes  indistinct,  when  the  object  is  placed  at  less  than  15 
centimetres  (6  inches)  from  the  eye. 

Between  these  two  limits,  of  15  centimetres  and  infinity,  the  accom- 
modation required  is  by  no  means  in  simple  proportion  to  the  distance. 
The  accommodation  necessary  for  objects  situated  respectively  at  15 
and  30  centimetres  from  the  eye  (6  inches  and  12  inches),  is  much 
greater  than  for  the  distances  of  one  yard  and  two  yards.  The 
farther  the  object  recedes  from  the  eye,  the  less  difference  is  pro- 
duced, in  the  divergence  of  the  rays,  by  an  additional  distance ;  and 
consequently  less  change  is  required  in  the  refractive  condition  of 
the  eye.  It  is  generally  found  that  no  sensible  effort  of  accommoda- 
tion is  needed  for  objects  situated  beyond  fifty  feet  from  the  observer ; 
while  within  this  limit  the  accommodation  necessary  for  distinct  vision 
increases  rapidly  with  the  diminution  of  distance. 

An  eye  which  is  capable  of  distinct  vision,  throughout  the  whole 
range  between  15  centimetres  and  an  indefinite  distance,  is,  in  this 
respect,  a  normal  eye,  and  is  said  to  be  emmetropic ;  that  is,  its 
powers  of  accommodation  are  within  the  natural  limits  or  measure- 
ments of  this  function. 

Presbyopic  Eye. — The  power  of  accommodation  naturally  diminishes 
with  the  advance  of  age ;  and  observation  shows  that  this  diminution 
dates  from  the  earliest  period  of  life.  Infants  often  examine  minute 
objects  at  very  short  distances,  in  a  manner  which  would  be  imprac- 
ticable for  the  healthy  adult  eye;  and  the  minimum  distance  of  dis- 
tinct vision  at  twenty  years  of  age  is  placed  by  some  writers  at  ten 
centimetres  instead  of  fifteen.  The  power  of  increasing  the  convexity 
of  the  lens  to  this  extent  is  soon  lost ;  and,  as  it  continues  to  diminish, 
a  time  arrives,  usually  between  the  ages  of  40  and  50  years,  when  the 
incapacity  of  accommodation  for  near  objects  begins  to  interfere  with 
the  ordinary  occupations  of  life.  When  this  condition  is  reached,  the 
eye  is  said  to  be  presbyopic.  Its  vision  is  still  perfect  for  distant 
objects,  but  it  can  no  longer  adapt  itself  to  those  in  close  proximity. 
To  remedy  this  defect  the  patient  employs  a  convex  eye-glass,  which 
gives  him  an  increased  refraction  for  the  examination  of  near  objects; 
and  he  is  thus  enabled  to  read  or  write  at  ordinary  distances  and  in 
characters  of  the  ordinary  si/e. 

The  use  of  a  convex  eye-^lass  does  not  restore  the  perfection  of 
sight  a.-  il  exited  beforehand.  In  the  normal  eye,  the  deirrec  of 


THE    SENSES. 


545 


accommodation  varies  for  every  change  of  distance  within  fifty  feet ; 
and  the  organ  is  thus  adjusted  by  an  instantaneous  and  unconscious 
movement,  for  the  most  delicate  variations  of  refractive  power.  But 
an  eye-glass,  the  curvatures  of  which  are  invariable,  can  give  perfect 
correction  only  for  a  single  distance.  A  glass  is,  therefore,  usually 
selected  of  such  curvature  as  to  serve  for  the  most  convenient  dis- 
tance in  ordinary  manipulations. 

Myopic  Eye. — In  many  instances,  where  the  eye  is  otherwise  normal, 
its  antero-posterior  diameter  is  longer  than  usual,  thus  placing  the  retina 
at  a  greater  distance  behind  the  lens.  Consequently,  although  the 
rays  are  brought  to  a  focus  at  the  usual  distance  behind  the  cornea,  this 
focus  is  situated  in  the  vitreous  body ;  and  the  rays  reach  the  retina  only 
after  their  crossing  and  partial  dispersion  (Fig.  143).  This  produces 
indistinct  vision  for  remote  objects.  But  for  those  at  shorter  distances? 


FIG.  142. 


EMMETEOPIC  EYE,  in  vision  at  long  distances.    fWundt.3 

FIG.  143. 


MYOPIC  EYE,  in  vision  at  long  distances.    (Wundt.) 

the  rays  enter  the  pupil  under  such  a  divergence,  that  their  focus  falls 
at  the  retina,  and  the  object  is  distinctly  seen.  Such  an  eye  is  said  to 
be  myopic,  or,  in  ordinary  language,  "near  sighted,"  because  its  range 
of  distinct  vision  is  confined  to  comparatively  near  objects.  The  flexi- 
bility of  the  lens,  and  its  capacity  for  increased  convexity,  may  be,  in 
the  myopic  eye,  fully  up  to  the  normal  standard,  and  consequently  its 
power  of  accommodation  may  be  as  great  as  that  of  the  normal  eye. 
In  the  emmetropic  condition,  a  certain  variation  in  the  curvature  of 
the  lens  produces  the  requisite  accommodation  for  all  distances  be- 
tween 15  centimetres  and  infinity.  In  the  myopic  eye  the  same  accom- 
modating power  may  be  exercised  between  the  distances  of  8  and  20 
centimetres.  The  myopic  eye  consequently  has  distinct  vision  at 

2K 


546  THE    NERVOUS    SYSTEM. 

shorter  ranges  than  a  normal  one,  but  gives  an  imperfect  image  for 
remote  objects. 

The  remedy  employed  for  the  myopic  eye  is  a  concave  eye-glass, 
which  increases  the  divergence  of  the  incident  rays.  This  serves  to 
carry  the  focus  of  parallel  or  nearly  parallel  rays  farther  backward,  so 
that  it  falls  upon  the  retina,  producing  distinct  vision.  As  the  accom- 
modating power  is  normal  in  amount,  this  contrivance  restores  the  per- 
fection of  sight,  if  the  eye  be  otherwise  well-formed ;  and  the  patient 
can  then  accommodate  for  all  distances  within  the  natural  limits  of 
distinct  vision. 

Apparent  Position  of  Objects,  and  Binocular  Vision. — The  apparent 
position  of  an  object  is  determined  by  the  direction  in  which  the  lumi- 
nous rays  coming  from  it  enter  the  eye.  The  perception  of  light  neces- 
sarily marks  the  direction  in  which  it  has  arrived,  and  therefore  the 
apparent  position  of  its  source.  It  is  difficult  to  understand  fully  the 
physiological  cause  for  this  appreciation  of  the  path  followed  by  a 
luminous  beam  ;  though  it  seems  probable  that  it  may  be  connected 
with  the  position  of  the  rods  and  cones,  which  are  everywhere  perpen- 
dicular to  the  curved  surface  of  the  retina,  and  thus  receive  the  impres- 
sion of  a  ray,  if  at  all,  in  the  direction  of  their  longitudinal  axes.  But 
whatever  may  be  the  optical  mechanism  of  the  process,  its  result  is 
that  a  ray  coming  from  below  attracts  attention  to  the  inferior  part  of 
the  field  of  vision  ;  and  one  coming  from  above  is  referred  to  the  upper 
part  of  the  same  field.  Thus  if  two  luminous  points  appear  simulta- 
neously in  the  field  of  vision,  they  present  themselves  in  a  certain  posi- 
tion with  regard  to  each  other,  above  or  below,  to  the  right  or  the 
left,  according  to  the  direction  in  which  their  light  has  reached  the  eye. 

It  is  evident  accordingly  that  the  lower  half  of  the  retina  receives  the 
rays  coming  from  above,  and  its  upper  half  those  coming  from  below ; 
while  the  right  half  of  the  visual  field  is  perceived  by  the  left  half  of 
the  retina,  and  vice  versa.  The  image  formed  upon  the  retina  is  con- 
sequently an  inverted  and  reversed  image  of  the  object.  But  as  it  is 
the  direction  of  the  visual  ray  at  its  impact  on  the  retina  which  deter- 
mines the  apparent  position  of  its  source,  objects  will  appear  erect, 
though  their  images  on  the  retina  are  inverted;  and  the  eye  perceives 
every  object  in  the  field  of  vision  above  or  below,  to  the  right  or  left, 
according  to  the  position  which  it  really  occupies  in  regard  to  the  centre 
of  the  field  and  the  line  of  direct  vision. 

Point  of  Fixation,  in  Vision  with  Two  Eyes. — For  either  eye,  distinct 
perception  is  possible,  as  shown  above  (p.  538),  only  for  objects  in  a 
single  range,  known  as  the  "  line  of  direct  vision."  Since  the  eves  are 
placed  in  their  orbits  at  a  lateral  distance  from  each  other  of  about  six 
centimetres,  when  they  are  both  directed  at  the  same  object,  within  a 
moderate  distance,  their  lines  of  direct  vision  have  a  sensible  conver- 
gence, and  meet  at  a  certain  point.  At  this  intersection  of  the  t  \vo  lines 
of  direct  vision,  an  object  may  be  seen  distinctly  by  both  eyes.  But 
at  every  other  point  it  must  appear  indistinct  to  one  of  them  ;  because 


THE    SENSES. 


547 


if  in  the  line  of  direct  vision  for  the  right  eye  it  will  be  out  of  that  line 
for  the  left  eye,  and  vice  versa.  There  is,  accordingly,  only  a  certain 
distance,  directly  in  front,  at  which  an  object  can  be  distinctly  seen  sim- 
ultaneously by  both  eyes ;  namely,  that  at  which  the  two  lines  of  direct 
vision  coincide.  This  point  is  called  the  point  of  fixation  for  the  two 
eyes.  In  fixing  any  object,  for  binocular  vision,  the  accommodation 
in  each  eye  is  adjusted  for  the  required  distance ;  and  thus  the  entire 
accuracy  of  both  organs  is  concentrated  upon  a  single  point. 

Since  it  is  the  position  of  the  two  eyes  in  their  orbits  which  deter- 
mines the  point  of  fixation,  the  observer  can  form  a  tolerably  accurate 
judgment,  as  to  whether  another  person  within  a  moderate  distance  be 
looking  at  him,  or  at  a  different  object  in  the  same  direction.  For 
greater  distance?  the  estimate  fails,  because  the  obliquity  of  the  eyes, 
in  looking  at  remote  objects,  is  so  small  that  its  variation  is  no  longer 
appreciable. 

Single  Vision  with  both  Eyes. — It  is  evident  from  the  preceding  that 
there  can  be  only  one  point  in  the  line  of  direct  vision  for  both  eyes  at  the 
same  time.  When  an  object  occupies  this  situation,  namely,  the  point 
of  fixation,  it  is  distinctly  perceived  by  each  eye  in  the  centre  of  the 
field  of  vision  ;  thus  its  two  visual  images  exactly  cover  each  other  and 
so  form  but  one.  Consequently,  the  object  appears  single,  though 
seen  by  both  eyes.  But  if  placed  either  within  or  beyond  the  point  of 
fixation,  it  will  appear  indistinct  and  at  the  same 
time  double.  If  the  observer  hold  a  slender  rod 
in  the  vertical  position  at  a  distance  of  one  or 
two  feet  before  the  face,  and  in  the  same  range 
with  any  small  object,  such  as  a  door-knob,  on 
the  opposite  side  of  the  room,  it  will  be  found 
that  when  both  eyes  are  directed  at  the  rod,  it 
is  seen  single  and  distinctly,  but  the  door-knob 
appears  double,  one  of  its  images  falling  on  each 
side.  If  the  eyes  be  now  directed  at  the  door- 
knob, that  in  turn  becomes  distinct  and  single, 
while  the  figure  of  the  rod  is  double,  one  indis- 
tinct image  appearing  on  each  side,  as  before. 

These  phenomena  depend  on  the  different  direc- 
tions of  the  two  lines  of  vision.  When  the  nearer 
object  (Fig.  144,^  occupies  the  point  of  fixation, 
the  farther  object  (2)  will  also  be  seen,  because  it 
is  still  included  in  the  visual  field;  though  it 
will  be  seen  indistinctly,  because  the  accommoda- 
tion of  the  eye  is  not  adjusted  to  its  distance,  and 
because  it  is  not  in  the  direct  line  of  sight.  But 
for  the  right  eye  (a)  it  will  be  placed  to  the  right 
of  this  line,  and  for  the  left  eye  (6)  to  the  left  of  it. 
Its  two  images  do  not  correspond  with  each  othe_ 
in  situation,  and  it  accordingly  appears  double. 


SINGLE  AND  DOUBLE  VISION, 
at  different  distances. — a. 
Right  eye.  b.  Left  eye.  1. 
Object  at  the  point  of  fixa- 
tion, seen  single.  2.  Object 
beyond  the  point  of  fixa- 
tion, seen  double. 


548  THE    NERVOUS    SYSTEM. 

When  the  eyes,  on  the  other  hand,  are  directed  to  the  more  distant 
object,  the  nearer  one  is  no  longer  at  the  point  of  fixation.  For  the 
right  eye,  its  image  will  appear  to  the  left  of  the  line  of  sight,  and 
for  the  left  eye  to  the  right  of  this  line.  It  therefore  becomes  double 
and  indistinct. 

Thus,  in  ordinary  binocular  vision  every  object  but  one  appears 
double  and  indistinct.  This  circumstance  is  so  little  noticed  that  it 
never  causes  confusion  of  sight,  and  even  requires  a  special  experi- 
ment to  demonstrate  its  existence.  The  reason  for  its  passing  unob- 
served is  twofold.  First,  the  attention  is  naturally  concentrated  upon 
the  object  at  the  point  of  fixation.  When  this  point  is  shifted,  each 
new  object  upon  which  it  falls  appears  single ;  and  thus  the  idea  of  a 
double  image,  even  if  indistinctly  suggested  at  any  time,  is  at  once 
dispelled  by  the  movement  of  the  eyes  in  that  direction.  Secondly, 
an  object  placed  toward  either  side  will  form  a  double  image,  since  its 
apparent  position  is  different  for  the  two  eyes.  But  the  obliquity  of 
its  rays,  and  consequently  the  indistinctness  of  its  image,  will  be  greater 

FIG.  145.  FIG.  146. 


AS  SEEN  BY  THE  LEFT  EYE.  As  SEEN  BY  THE  RIGHT  EYE. 

for  the  right  eye  than  for  the  left,  or  vice  versa ;  and  the  notice  of  the 
observer,  if  drawn  to  it  at  all,  is  occupied  with  the  more  distinct  of 
the  two  images,  to  the  exclusion  of  the  other.  The  fact  becomes 
palpable  only  in  such  an  experiment  as  the  above,  where  the  bodies 
examined  are  in  the  same  linear  range,  so  that  the  double  images  pro- 
duced are  equal  in  intensity,  and  sufficiently  contrasted  with  surround- 
ing objects  to  attract  attention. 

Double  vision  may  be  produced  at  any  time  by  pressure  at  the  outer 
angle  of  one  eye,  so  as  to  alter  its  position  in  the  orbit,  the  other  eye 
iriii;iinin,ir  fixed.  But  in  this  case  the  whole  field  of  vision  is  displaced, 
and  all  objects  are  doubled  indiscriminately.  This  form  of  double  vis- 
ion is  produced,  in  vertigo  or  intoxication,  by  irregular  action  of  the 
muscles  of  the  eyeball. 

Appreciation  of  Solidity  and  Projection. — When  both  eyes  are 


THE    SENSES.  549 

directed  at  a  single  object,  its  distance  may  be  estimated  with  some 
accuracy  by  the  convergence  of  the  visual  axes  required  for  its  fixa- 
tion. Another  impression  is  also  produced  by  binocular  vision,  when 
an  object,  of  appreciable  volume  and  thickness,  is  viewed  within  a  mod- 
erate distance.  Owing  to  the  lateral  separation  of  the  two  eyes,  and 
the  convergence  of  their  visual  axes,  they  do  not  receive  precisely  the 
same  image.  Both  eyes  will  see  the  front  of  the  object  in  nearly  the 
same  manner  ;  but  in  addition  the  right  eye  will  see  a  little  of  its  right 
side,  and  the  left  eye  a  little  of  its  left  side.  This  is  illustrated  in  Figs. 
145  and  146,  representing  an  object  as  seen  by  the  two  eyes,  at  a  dis- 
tance of  eighteen  inches  or  two  feet ;  rather  more  of  the  details  on  one 
side  being  visible  to  the  left  eye,  and  rather  more  of  those  on  the  other 
side  to  the  right  eye.  As  the  central  part  of  its  mass  is  in  the  point 
of  fixation,  at  the  junction  of  the  visual  axes,  the  object  appears  single. 
But  the  images  which  it  presents  to  the  two  eyes  are  not  precisely 
identical ;  and  the  combination  of  these  different  images  into  one  gives 
the  impression  of  solidity  and  projection. 

This  effect  is  complete  only  when  the  object  is  within  a  moderately 
short  distance.  For  those  which  are  remote,  the  convergence  of  the 
visual  axes,  and  the  consequent  difference  in  configuration  of  the  im- 
ages, become  inappreciable,  and  the  impression  of  solidity  disappears. 
At  a  distance  of  some  miles  even  a  large  object,  like  a  mountain,  loses 
its  projection,  and  appears  like  a  flattened  mass  against  the  horizon. 
The  pictorial  representation  of  distant  views  is  therefore  often  very 
effective,  the  idea  of  remoteness  in  different  parts  of  the  landscape 
being  conveyed  by  appropriate  intersections  of  outline  and  by  varia- 
tions in  tone,  color,  and  distinctness,  like  those  due  to  the  interposition 
of  the  atmosphere.  But  a  picture  which  aims  to  represent  the  solidity 
of  near  objects  can  never  deceive  us  in  this  respect,  however  elaborate 
its  details ;  since  its  surface  presents  the  same  image  to  both  eyes,  and 
it  is  consequently  evident  that  the  objects  delineated  have  no  real  pro- 
jection. But  the  appearance  of  solidity  may  be  successfully  imitated  by 
representing  an  object  in  two  different  positions.  This  is  the  principle 
of  the  stereoscope.  Two  photographic  pictures  of  the  same  object  are 
taken  from  different  points  of  view,  one  of  them  representing  it  as  it 
would  be  seen  by  the  right  eye,  and  the  other  as  it  would  be  seen  by 
the  left.  With  these  pictures  so  placed  in  the  stereoscope  that  each 
eye  has  presented  to  it  the  appropriate  view,  the  two  images  are  com- 
bined in  the  act  of  vision,  producing  the  apparent  effect  of  projection 
and  solidity. 

General  Laws  of  Visual  Perception. — Beside  the  formation  and  com- 
bination of  optical  images,  there  are  certain  phenomena  connected  with 
visual  perceptions  in  general  which  are  of  interest  in  the  physiology 
of  sight.  Some  of  these  phenomena  require  special  modes  of  investi- 
gation, while  others  are  made  evident  by  comparatively  simple  means, 
and  are  often  important  in  their  hygienic  relations. 

Luminous  impressions  upon  the  eye  continue  for  a  short  time  after 


550  THE    NERVOUS    SYSTEM. 

cessation  of  the  light. — The  persistence  of  these  impressions  is  not  usu- 
ally noticeable,  because  they  are  immediately  followed  by  others  on  the 
same  part  of  the  retina,  and  are  thus  practically  obliterated.  But,  if 
the  momentary  impression  be  not  at  once  followed  by  a  different  one, 
or  if  sufficiently  vivid  to  be  perceived,  notwithstanding  the  presence  of 
others,  it  may  be  made  evident  to  observation.  If  a  bright  point,  like 
the  heated  end  of  a  wire,  be  carried  round  in  a  circle  in  a  dark  room 
with  moderate  rapidity,  the  eye  follows  it  throughout.  But  if  the  ra- 
pidity of  its  movement  be  increased,  it  appears  drawn  out  more  or  less 
into  a  curved  line ;  and,  when  moving  with  very  high  velocity,  it  be- 
comes transformed  into  a  continuous  circle  of  light,  since  its  impres- 
sion upon  the  retina,  when  at  one  part  of  the  circle,  lasts  until  it  has 
completed  its  revolution  and  returned  to  the  same  point.  The  sparks 
thrown  off  in  rapid  succession  from  a  knife-grinder's  wheel  produce  the 
effect  of  an  unbroken  stream  of  fire.  A  circular  saw  with  large  teeth, 
revolving  under  high  speed,  presents  apparently  a  smooth  edge,  formed 
by  the  moving  points  of  the  teeth ;  and  the  spokes  of  a  rapidly-turning 
wheel  become  confused  upon  the  retina  with  the  intervening  spaces, 
and  assume  the  appearance  of  a  glimmering  disk. 

The  duration  of  visual  impressions  cannot  be  expressed  by  any  single 
term  which  would  be  correct  for  all  cases.  A  brilliant  light  leaves,  on 
the  whole,  a  longer  impression  than  a  feeble  one ;  but,  on  the  other 
hand,  its  relative  intensity  to  surrounding  objects  diminishes  more 
rapidly,  and  it  consequently  requires,  if  in  motion,  a  higher  velocity 
to  produce  the  appearance  of  a  uniform  bright  line.  The  time  during 
which  luminous  impressions  remain,  without  appreciable  diminution 
of  their  intensity,  is  usually  tested  by  means  of  revolving  disks,  varie- 
gated in  equal  sectors  of  black  and  white.  The  rate  of  revolution  being 
known,  as  well  as  the  width  of  the  sectors,  when  the  revolving  surface 
presents  a  uniform  gray  tint,  the  time  during  which  the  visual  impres- 
sion remains  undiminished  is  readily  calculated.  The  result  of  such 
experiments  gives  the  duration  of  undiminished  impressions,  for  revolv- 
ing disks  under  moderate  illumination,  as  one-twenty-fourth  of  a  second; 
and,  for  the  oscillation  of  a  very  luminous  point  following  the  vibrations 
of  a  tuning-fork,  one-thirtieth  of  a  second. 

The  persistence  and  apparent  continuity  of  successive  visual  images 
are  illustrated  by  the  Thaumatrope  and  other  similar  contrivances,  in 
which  a  number  of  pictures,  representing  the  same  object  in  different 
positions,  are  made  to  pass  in  quick  succession  before  the  eye.  The 
intervals  between  them  are  too  short  to  be  observed,  and  the  figure 
appears  as  if  in  motion. 

Duration  of  a  Luminous  Impulse  necessary  for  its  Perception. — 
Tliis  point  has  been  investigated  by  Rood*  by  means  of  the  electric 
spark  from  an  induction  coil  connected  with  a  Leyden  jar.  The  dura- 

*  American  Journal  of  Science  and  Arts.     New  Haven,  September,  1871. 


-t- 


S 


THE    SENSES.  551 

tion  of  the  spark  obtained  on  breaking  the  primary  current  was  meas- 
ured by  the  aid  of  an  apparatus  arranged  as  in  Fig.  14T. 

The  light  emanating  from  the  spark,  S,  was  received  by  an  achro- 
matic lens,  L.  It  then  fell  upon  a  plane  mirror  revolving  with  a  uni- 
form velocity  of  540  per  second,  and,  after  reflection,  was  brought  to  a 
focus  upon  a  glass  plate,  G,  where  it  could  be  examined  by  the  eye- 
piece, E,  magnifying  ten  diameters. 
From  the  known  rate  of  revolution  FIG.  147. 

of  the  mirror,  and  its  distance  from 
the  plate  G,  the  rapidity  of  motion  of 
the  reflected  beam  upon  the  plate  was 
determined.  If  the  spark  lasted  long 
enough  for  its  reflected  image  to  move 
over  an  appreciable  distance,  it  would 
appear  to  be  drawn  out  in  a  linear 
form,  owing  to  the  persistence  of  its 
visual  impression.  But  with  the  mir- 
ror revolving  at  this  speed  no  such 
alteration  was  perceptible,  the  reflected 
spark  appearing  as  if  stationary :  show-  AppA?ATUS  for  measuring  the  duration  of 

„    ,      ,        '  an  electric  spark.— S.  Position  of  the  spark, 

mg  that  tne  duration  Of  the  light  COUld        L.  Achromatic  lens.     M.  Revolving  mir- 

not  be  greater  than  .000002  GoTiW)      T^G-  G1f s p^ f?r  receiving  the ima%Q 

V500000/        of  the  spark.    E.  Telescope  eye-piece. 

of  a  second. 

In  subsequent  experiments,  there  was  interposed  between  the  spark 
and  the  mirror  a  glass  plate,  ruled  with  alternate  transparent  and  opaque 
lines,  2T4  of  a  millimetre  in  width.  Its  image,  when  illuminated  by  the 
spark,  would  appear  upon  the  plate,  G,  as  a  series  of  black  and  white 
lines.  With  the  mirror  in  motion,  if  the  illumination  lasted  long 
enough  for  the  image  to  be  shifted  a  distance  equal  to  the  combined 
width  of  a  black  and  white  line,  these  lines  would  become  undistin- 
guishable  from  each  other  as  in  the  revolving  disk  with  black  and 
white  sectors.  Thus  the  continuance  of  the  visible  lines,  under  a  given 
rate  of  motion,  proved  that  the  duration  of  the  electric  spark  was  less 
than  a  certain  calculable  period.  The  result  showed  that  the  shortest 
measurable  spark  lasted  but  little  over  .00000004  G^oVow)  °f  a 
second. 

With  a  spark  of  this  duration,  motionless  objects  were  distinctly 
visible.  The  letters  on  a  printed  page  could  be  recognized,  and  even 
the  polarization  of  light  was  plainly  observable.  It  was  accordingly 
sufficient  to  produce  a  complete  retinal  impression. 

These  experiments  do  not  indicate  the  time  required  for  nervous 
action  in  the  perception  of  light.  They  only  show  that  a  luminous 
impulse  having  the  above  duration  is  sufficient  to  excite  the  sensibility 
of  the  retina.  But  the  time  required  for  perceiving  the  sensation  is 
very  much  longer.  From  the  results  given  in  a  preceding  chapter 
(page  371)  it  appears  that  the  passage  of  a  visual  impression  through 
the  optic  nerve  would  require  at  least  y^1^  of  a  second,  and  its  percep- 


552  THE    NERVOUS    SYSTEM. 

tion  in  the  brain  considerably  more.  It  follows  from  this  that,  at  the 
instant  when  the  electric  spark  is  seen,  it  has,  in  fact,  already  come 
to  an  end ;  the  interval  which  elapses  before  it  is  perceived  by  the 
observer  being  very  much  greater  than  its  actual  duration. 

This  accounts  for  a  peculiar  effect,  often  observed  under  the  use  of 
the  electric  spark,  namely :  that  bodies  in  rapid  motion,  when  illumi- 
nated by  an  instantaneous  discharge,  appear  as  if  at  rest.  A  disk  with 
black  and  white  sectors,  in  revolution  under  continuous  light,  appears 
of  a  uniform  gray.  But  if  such  a  disk,  revolving  in  a  dark  room,  be 
illuminated  by  the  electric  spark,  it  becomes  visible  for  an  instant,  with 
its  sectors  as  distinct  from  each  other  as  if  they  were  at  rest.  A  jet 
of  water,  flowing  from  a  narrow  orifice,  is  transparent  in  its  upper  part, 
but  turbid  lower  down ;  and  by  instantaneous  illumination  the  turbid 
portion  is  seen  to  be  composed  of  separate  drops,  which  appear  motion- 
less. The  passage  of  a  cannon-ball  or  a  bullet  by  daylight  is  imper- 
ceptible ;  because  it  does  not  remain  long  enough  at  any  one  point  to 
efface  the  persistent  impression  of  objects  behind  it.  But  if  such  a  mis- 
sile should  happen  to  be  passing  in  front  of  the  observer  in  the  night 
during  a  thunder-storm,  at  the  moment  of  a  flash,  it  would  be  equally 
visible  with  other  objects,  and  would  appear  as  if  suspended  motionless 
in  the  air. 

The  momentary  closure  of  the  eyes  in  winking,  for  the  same  reason, 
is  unnoticed,  and  causes  no  interference  with  sight ;  since  the  visual 
impression  of  external  objects  continues  unimpaired  during  the  interval 
occupied  by  the  movement  of  the  lids. 

The  sensibility  of  the  retina  is  diminished  by  continued  impressions. 
— This  diminution  seems  to  take  place  from  the  very  commencement  of 
a  visual  impression,  so  that  it  may  be  perceptible  within  a  few  seconds. 
When  the  image  of  the  retinal  blood-vessels  is  made  apparent  by  chang- 
ing the  position  of  their  shadows  (page  530)  their  figures  are  visible 
for  an  instant  with  extreme  sharpness.  But  they  at  once  begin  to  fade 
and  soon  become  imperceptible.  The  portions  of  the  retina  under  full 
illumination  have  their  sensibility  so  rapidly  diminished,  that  the 
shadow,  if  motionless,  is  no  longer  visible  by  contrast.  Those  in 
shadow,  on  the  other  hand,  become  more  sensitive  by  repose ;  and 
when  the  shifting  of  the  light  brings  them  again  into  illumination, 
they  are  already  more  susceptible  to  its  influence. 

If  one  eye  be  covered  by  a  dark  glass,  and  the  other  used  alone  for 
reading  or  writing,  at  the  end  of  an  hour  the  difference  in  retinal  sen- 
sibility of  the  two  will  be  very  apparent.  A  faintly  luminous  object 
in  a  dark  room  may  be  almost  imperceptible  to  the  eye  which  has  been 
in  use,  while  appearing  to  the  other  quite  brilliant.  But  this  condition 
is  transitory ;  and  by  covering  the  eye  previously  in  use,  and  reading 
or  writing  with  the  other,  the  fatigued  organ  recovers  its  sensibility, 
and  that  which  was  before  the  most  sensitive  becomes  less  so. 

The  diminution  and  recovery  of  retinal  si-risibility,  under  excitement 
and  repose,  is  connected  with  the  phenomena  of  negative  images. 


THE    SENSES.  553 

If  the  eye  be  fixed  for  a  short  time  upon  a  white  spot  in  a  black 
ground,  and  then  suddenly  directed  toward  a  blank  wall  of  white 
or  light  gray  color,  a  dark  spot  will  appear  upon  it,  of  the  same  size 
and  figure  with  the  white  one  previously  observed.  This  is  the  "  nega- 
tive image  "  of  the  retinal  impression.  That  part  of  the  retina  which 
was  first  impressed  by  the  rays  from  the  white  spot  becomes  less  sensi- 
tive ;  and  another  white  surface,  looked  at  immediately  afterward, 
appears  dark.  On  the  other  hand,  those  parts  which  were  exposed 
only  to  the  dark  ground,  that  is,  to  the  comparative  absence  of  light, 
are  more  sensitive  than  before ;  and  the  surface  of  the  white  wall,  out- 
side the  central  spot,  consequently  appears  brighter.  If  a  piece  of 
dark  furniture  against  a  white  or  gray  wall  be  looked  at  steadily  for  a 
short  time,  on  shifting  the  eyes  to  a  different  part  of  the  wall,  the  figure 
of  the  chair  or  table  will  appear,  with  all  its  details  of  outline,  expressed 
in  a  lighter  tint  than  that  of  the  surrounding  parts. 

Negative  images  may  be  produced  in  a  still  more  simple  manner. 
Let  a  black  ruler,  about  one  inch  wide,  be  laid  upon  a  sheet  of  white 
paper,  and  looked  at  steadily  for  thirty  or  forty  seconds.  If  the  ruler 
be  now  suddenly  removed,  the  eye  remaining  fixed,  its  image  will 
appear  as  a  bright  band  upon  the  paper,  gradually  fading  as  the  retinal 
sensibility  becomes  equalized. 

The  sensibility  of  the  retina  may  be  separately  increased  or  dimin- 
ished for  different  colors.  If  a  black  ruler  be  laid  upon  a  blue  cloth, 
on  taking  it  away  a  band  appears  in  its  place  of  a  more  intense  blue 
than  the  rest ;  and  if  placed  upon  a  red  cloth,  its  negative  image  is 
of  a  remarkably  pure  red,  the  remainder  appearing  of  a  dull  brown. 
But  parts  of  the  retina  which  have  been  fatigued  by  the  continued 
impression  of  one  color  are  more  sensitive  to  rays  of  the  complemen- 
tary hue ;  since  the  latter  have  been  for  a  certain  time  excluded.  A 
strip  of  red  paper,  placed  on  a  white  ground  and  suddenly  removed, 
leaves  an  image  which  is  bluish-green  ;  and  a  green  one  leaves  an  image 
with  a  tinge  of  red.  The  light  from  the  white  ground  really  contains 
all  the  colors ;  but  an  eye  which  has  become  less  sensitive  to  green  rays 
will  receive  an  impression  in  which  the  red  predominates,  and  vice 
versa. 

Owing  to  the  variable  sensibility  of  the  retina,  according  to  exposure, 
an  object,  under  some  conditions,  is  most  easily  perceived  by  indirect 
vision.  It  often  happens  that  a  small  and  feeble  star  may  be  momen- 
tarily perceived  by  looking,  not  directly  at  it,  but  at  some  point  in  its 
immediate  neighborhood.  The  star  is  not  seen  distinctly  under  these 
circumstances,  because  it  is  out  of  the  line  of  direct  vision.  But  its 
light  falls  upon  a  part  of  the  retina  near  the  fovea  centralis,  where  the 
sensibility  is  more  acute  than  usual,  owing  to  its  previous  exposure 
only  to  the  dark  sky ;  while  the  fovea  itself,  which  has  been  receiving 
in  succession  the  images  of  various  stars,  is  comparatively  deficient  in 
sensibility.  When  the  visual  axis  is  turned  directly  upon  the  faint 


554  THE    NERVOUS    SYSTEM. 

star,  in  order  to  get  a  distinct  view,  its  light  disappears.     It  can  only 
be  seen  as  an  evanescent  object  by  indirect  vision. 

Sense  of  Hearing. 

By  the  sense  of  hearing  we  receive  the  impressions  of  sound,  and 
appreciate  their  intensity,  their  higher  or  lower  notes,  and  their  quality, 
that  is,  the  different  character  of  sounds  of  similar  pitch  and  intensity, 
produced  by  different  means,  as  by  reeds,  strings,  or  wind  instruments, 
or  the  concussion  of  solid  or  liquid  bodies.  Our  idea  of  time,  or  the 
succession  of  events,  seems  also  especially  connected  with  auditory 
sensations.  Impressions  received  in  this  way  depend  on  the  vibrations 
excited  in  the  atmosphere  by  sonorous  bodies,  which  are  themselves 
already  in  vibration.  These  undulations,  when  communicated  to  the 
auditory  apparatus,  produce,  through  it,  the  sensation  of  sound. 

Organ  of  Hearing. — The  organ  of  hearing  consists  of,  first,  the  exter- 
nal ear,  a  trumpet-shaped  expansion,  which  collects  the  sonorous  im- 
pulses coming  from  various  quarters,  and  conducts  them  into  its  tubu- 
lar continuation,  the  external  auditory  meatus  ;  secondly,  a  membranous 
sheet  or  drum-head,  the  membrana  tympani,  stretched  across  the  audi- 
tor v  meatus,  by  which  the  vibrations  are  received  and  transmitted, 
through  the  chain  of  bones  in  the  tympanum,  to  the  labyrinth,  or 
internal  ear ;  a  cavity  in  the  petrous  portion  of  the  temporal  bone,  con- 
taining various  membranous  sacs  and  canals,  upon  which  are  distributed 
the  filaments  of  the  auditory  nerve. 

Thus  the  terminal  expansions  of  the  auditory  nerve,  deeply  concealed 
in  their  bony  cavities,  and  sustained  by  the  surrounding  fluids,  while 
protected  from  all  other  mechanical  impressions,  are  so  placed  as  to 
receive  the  impulse  of  sound. 

External  Ear. — The  external  ear  is  a  cartilaginous  framework, 
covered  with  integument,  and  more  or  less  movable  by  various  muscles, 
which  turn  it  in  various  directions.  In  man,  these  muscles  are  nearly 
inactive  ;  though  ia  exceptional  cases  they  can  produce  a  partial  sliding 
or  rotatory  movement  of  the  ear.  In  most  quadrupeds,  on  the  other 
1), iiid,  the  movements  are  vigorous  and  extensive,  and  greatly  aid  in 
the  sense  of  hearing,  by  enabling  the  organ  to  catch  distinctly  the  son- 
orous vibrations,  from  whatever  quarter  they  come.  They  also  serve 
to  indicate  the  direction  of  a  sound,  since  the  animal  ascertains,  by 
placing  the  ear  in  different  positions,  the  region  from  which  it  is  received 
with  greatest  distinctness. 

Membrana  Tympani  and  Chain  of  Bones. — The  membrana  tympani 
is  a  circular  fibrous  sheet  not  more  than  0.05  millimetre  in  thickness, 
but  quite  strong,  consisting  of  circular  and  radiating  tendinous  fibres, 
with  a  trace  of  intermingled  elastic  tissue.  Its  outer  and  inner  surfaces 
respectively  are  covered  by  thin  continuations  of  the  integument  of  the 
external  auditory  meatus,  and  of  the  lining  membrane  of  the  tympanic 
cavity;  and  the  three  layers  combined  form  a  membrane  about  0.10 
milliiiH-trc  in  thickness. 


THE    SENSES.  555 

In  its  natural  position  the  membrane  is  drawn  inward,  by  its  attach- 
ment to  the  malleus,  in  such  a  way  as  to  present  a  funnel-shaped  depres- 
sion, the  deepest  point  of  which  corresponds  to  the  end  of  the  handle 
of  the  malleus.  According  to  Ilelmholtz,*  the  sides  of  this  depression 
are  convex,  somewhat  like  the  inner  surface  of  the  blossom  of  a  morning- 
glory.  It  is  only  along  a  line  corresponding  to  the  handle  of  the 
malleus,  that  the  meridian  of  the  funnel  is  a  nearly  straight  line ;  else- 
where the  radial  fibres  of  the  membrane  are  curved,  with  their  convexi- 
ties toward  the  external  auditory  meatus. 

As  the  only  attachment  of  the  membrana  tympani.  except  at  its 
border,  is  to  the  handle  of  the  malleus,  any  movement  of  this  bone 
inward  will  draw  the  membrane  in  the  same  direction,  deepen  its  cen- 
tral depression,  and  put  its  fibres  upon  the  stretch.  On  the  other  hand, 
if  the  membrane  be  forced  outward,  it  will  draw  the  handle  of  the 
malleus  with  it ;  and,  finally,  if  the  elastic  and  muscular  attachments 
generally  be  in  equilibrium,  any  movement  of  the  membrane  will  be 
followed  by  a  corresponding  change  of  position  in  the  malleus. 

This  is  the  physiological  action  of  the  membrana  tympani.  From  its 
thinness  and  tension,  and  from  its  position  at  the  bottom  of  the  external 
auditory  meatus,  it  enters  into  vibration,  under  the  impulse  of  sounds 
from  the  exterior,  and  communicates  its  movement  to  the  handle  of 
the  malleus  at  its  inner  surface. 

The  chain  of  bones  consists  of  three  ossicles,  articulated  with  each 
other  by  their  extremities,  and  forming  a  zigzag  line  of  jointed  levers 
across  the  cavity  of  the  tympanum.  They  are 
known  respectively,  from  their  configuration, 
as  the  "malleus,"  "incus,"  and  "stapes,"  or 
the  hammer,  the  anvil,  and  the  stirrup.  The 
malleus  is  about  nine  millimetres  in  length,  of 
which  a  little  more  than  one-third  is  occupied 
by  the  rounded  head  and  the  neck,  and  a  lit-  OSSICLES  of  the  human  ear.— 
tie  less  than  two-thirds  by  the  comparatively  i^^laH^T*  3' 
straight  and  tapering  handle.  Its  very  slender 

lateral  process  projects  in  a  nearly  horizontal  direction  from  behind 
forward  in  the  natural  position  of  the  bone.  The  handle  is  the  only 
part  of  the  malleus  adherent  to  the  membrana  tympani,  the  neck  cor- 
responding to  the  upper  border  of  this  membrane,  while  the  head  pro- 
jects above  it,  lying  comparatively  free  in  the  tympanic  cavity.  It  is 
maintained  in  position  by  thin  ligamentous  bands  from  the  bony  wall 
of  the  cavity  inserted  into  its  head  and  neck,  and  by  the  tendon  of  the 
internal  muscle  of  the  malleus  or  "  tensor  tympani."  The  action  of  this 
muscle  is  to  draw  the  handle  of  the  malleus  inward,  tightening  the 
membrana  tympani,  and  rotating  the  head  of  the  bone  slightly  out- 

*  Mechanism  of  the  Ossicles  of  the  Ear.  Buck's  Translation.  New  York,  1873, 
p.  20. 


556 


THE    NERVOUS    SYSTEM. 


FlG.  149. 


ward.  When  in  movement,  the  malleus  oscillates  about  a  nearly  hori- 
zontal axis  situated  at  the  junction  of  its  handle  and  neck. 

The  head  of  the  malleus  is  articulated  with  the  incus  by  a  capsular 
joint  with  double-inclined  surfaces.  As  Helmholtz  has  shown,  these 
surfaces  have  such  an  inclination,  that  when  the  handle  of  the  malleus 
is  drawn  inward,  they  lock  together,  and  the  incus  follows  the  move- 
ment of  the  malleus ;  but  when  the  latter  bone  is  drawn  outward,  they 
inn  v  glide  upon  each  other,  without  necessarily  moving  the  incus. 

The  third  bone  of  the  middle  ear,  the  stapes,  has  a  close  resemblance 
in  form  to  its  namesake,  a  metallic  stirrup.  It  is  articulated  by  its 
angular  extremity  to  the  end  of  the  long  arm  of  the  incus  in  a  nearly 
horizontal  position.  Its  oval  base  corresponds  in  form,  and  nearly  in 
size,  with  the  fenestra  ovalis  of  the  bony  labyrinth,  in  which  it  is 

inserted ;  being  adherent  by 
its  surface  and  its  edges  to 
the  internal  periosteum  of 
the  labyrinth. 

The  stapes,  accordingly, 
forms  a  kind  of  movable  lid 
or  piston-head  occupying  the 
fenestra  ovalis,  and  capable 
of  transmitting  to  the  fluid 
of  the  labyrinth  the  impulses 
received  from  the  menibrana 
tympani :  The  extent  of  in- 
ward and  outward  movement 
of  the  base  of  the  stapes  has 
been  determined  by  Helm- 
holtz in  the  following:  man- 

RIGHT  TEMPORAL  BONE  of  the  new-born  infant,  seen  .  ° 

from  its  inner  si<l. •;  .-huwing  the  meinbrana  tympani      Her  :    The    Cavity  of   the   tym- 
and  chain  of  bones  in  their  natural  position.    (Rii-     panum    and  that  of  the  Vesti- 
bule having  been  opened  from 

above,  the  point  of  a  fine  sewing-needle  was  inserted  into  the  fibrous 
covering  of  the  base  of  the  stapes  on  the  side  of  the  vestibule,  and 
the  needle  allowed  to  rest,  near  its  insertion,  upon  an  adjacent  edge  of 
bone.  It  thus  formed  a  kind  of  index-lever,  which  would  indicate  by 
its  movement  very  slight  displacements  of  the  stapes.  The  stapes 
was  then  pressed  inward  and  outward,  as  freely  as  its  attachments 
would  allow,  either  by  direct  pressure  or  by  condensing  and  rarefy- 
ing the  air  in  the  external  auditory  meatus;  the  force,  in  the  latter 
case,  being  transmitted  through  the  membrana  tympani  and  chain  of 
bones.  The  movements  were  also  estimated  by  opening  the  superior 
semicircular  canal  of  the  labyrinth,  and  inserting  into  it  a  slender  glass 
tube  of  known  calibre,  a  portion  of  whirl),  as  well  as  the  vestibule,  was 
filled  with  water;  any  inward  pressure  being  indicated  by  a  corre- 
sponding rise  of  the  water-level  in  the  tnlie.  The  movement  of  the 
stapes,  in  these  experiments,  varied  from  .025  to  .072  millimetre. 


THE    SENSES.  557 

The  change  of  position  of  the  stapes  in  the  fenestra  ovalis,  from 
impulses  received  through  the  chain  of  bones,  is  not  a  simple  move- 
ment of  advance  and  recession,  but  a  rocking  motion,  in  which  its 
upper  border  is  tilted  back  and  forward.  This  action  of  the  stapes 
depends  on  the  varying  compactness  of  its  fibrous  attachments,  which 
allow  more  freedom  of  movement  above  than  below. 

The  position  of  the  stapes  is  also  regulated  by  the  action  of  the 
stapedius  muscle.  This  muscle,  the  smallest  in  the  body,  arises  from 
a  bony  canal  behind  the  tympanum  ;  its  slender  tendon  passing  almost 
directly  forward  to  be  inserted  into  the  neck  of  the  stapes,  near  its 
articulation  with  the  incus.  Its  contraction,  therefore,  draws  the 
angle  of  the  stapes  backward,  and  its  anterior  extremity  outward 
from  the  fenestra  ovalis. 

Physiological  Action  of  the  Bones  and  Muscles  of  the  Middle  Ear. 
—The  cavity  of  the  tympanum  is  an  irregularly  shaped  space,  across 
which  the  vibrations  received  by  the  membrana  tympani  are  trans- 
mitted by  the  chain  of  bones.  In  their  natural  position  and  with  their 
tendinous  connections  undisturbed,  these  bones  are  in  such  close  con- 
nection with  each  other  that  they  vibrate  as  a  single  body. 

The  action  of  the  internal  muscle  of  the  malleus,  or  tensor  tympani, 
is,  no  doubt,  as  its  name  indicates,  to  increase  the  tension  of  the  mem- 
brana tympani.  It  has  long  been  known  that,  after  opening  the  cavity 
of  the  tympanum  and  the  canal  in  which  this  muscle  is  lodged,  by  trac- 
tion upon  its  tendon  the  membrana  tympani  is  rendered  more  tense ; 
and,  according  to  Helmholtz,  all  the  ligaments  holding  the  ossicles  in 
place  are  at  the  same  time  put  upon  the  stretch. 

The  effect  produced  upon  hearing  by  increased  tension  of  the  mem- 
brana tympani  has  been  variously  interpreted.  Savart,*  who  first 
studied  systematically  the  vibration  of  stretched  membranes  induced 
by  the  proximity  of  sounding  bodies,  estimated  its  extent  from  the 
agitation  of  fine  sand  sprinkled  on  the  membranes ;  and  found  it  less 
pronounced,  other  things  being  equal,  when  the  tension  of  the  mem- 
brane was  increased.  He  applied  the  same  method  to  the  membrana 
tympani  of  man  and  animals,  and  found  that  sand,  sprinkled  on  its 
surface,  could  be  thrown  into  agitation  by  holding  near  it  a  sounding 
body,  and  that  these  phenomena  were  less  easy  of  production  when  the 
membrane  was  rendered  more  tense  by  traction  on  the  tensor  tympani. 
He  concluded  that  during  life  the  ear  is  more  susceptible  to  sounds  of 
a  given  intensity  when  the  membrana  tympani  is  relaxed  than  when 
it  is  on  the  stretch ;  and  that  the  tensor  tympani,  accordingly, 
exerts  a  protective  action  by  lessening  the  apparent  intensity  of 
loud  sounds. 

But  this  observer  was  not  aware  of  an  important  fact  established 
by  subsequent  investigations,  namely,  that  stretched  membranes,  like 
cords,  cannot  respond  indiscriminately  to  sounds  of  every  tone,  but 


*  Journal  de  Physiologie.     Paris,  1825,  tome  iv.,  p.  205. 


558  THE    NERVOUS    SYSTEM. 

only  to  a  certain  number  of  tones,  separated  by  definite  intervals;* 
and  that  they  will  respond  to  a  different  set  only  after  their  tension  has 
been  increased  or  diminished.  In  order,  therefore,  that  a  membrane 
may  be  easily  thrown  into  induced  vibration,  its  tension  must  corre- 
spond in  a  certain  ratio  with  the  tone  of  the  sounding  body. 

These  considerations  have  induced  a  different  view  of  the  tensor 
tympani  as  modifying  the  sensations  of  sound.  With  the  membrane 
in  a  state  of  moderate  tension,  a  certain  number  of  tones  only  are  dis- 
tinctly appreciated,  the  remainder  being  either  inaudible  or  indistinct. 
This  is  the  state  in  which  sounds  are  generally  perceived,  without 
exact  appreciation  of  their  relative  pitch.  But  when  the  ear  follows 
a  succession  of  tones,  or  when  it  listens  for  a  particular  note,  the 
tension  of  the  membrane  is  so  increased  or  diminished  as  to  transmit 
the  vibration  with  the  greatest  distinctness.  With  regard  to  modifica- 
tions in  the  apparent  intensity  of  sound,  it  is  probable  that  Savart's 
explanation  holds  good;  and  that  a  diminished  tension  of  the  mem- 
brane enables  the  ear  to  catch  more  readily  sounds  which  are  faint 
or  distant.  This  partial  relaxation  is  accomplished  by  the  stapedius 
muscle,  which  is  animated  by  a  filament  of  the  facial  nerve,  and  is 
therefore  more  directly  under  the  control  of  the  will ;  while  the  tensor 
tympani  is  supplied  from  the  otic  ganglion  of  the  sympathetic,  and  is 
involuntary  in  its  action. 

The  cavity  of  the  tympanum  communicates  with  the  pharynx  by 
the  Eustachian  tube.  The  existence  of  this  canal  secures  equality 
of  atmospheric  pressure  on  both  sides  of  the  membrrna  tympani, 
a  condition  essential  to  its  free  vibration  under  sonorous  impulses. 
The  external  barometric  pressure  varies  from  time  to  time ;  and  if  the 
middle  ear  were  a  closed  cavity,  this  variation  would  of  itself  chnnire 
the  tension  of  the  membrana  tympani  and  interfere  with  its  function. 
Although  the  walls  of  the  Eustachian  tube  are  habitually  in  contact 
with  each  other,  they  readily  yield  to  atmospheric  pressure  in  either 
direction,  and  thus  reestablish  the  equilibrium  between  the  outer  air 
and  the  cavity  of  the  tympanum. 

Labyrinth. — The  internal  ear,  or  labyrinth,  so  called  from  the  com- 
plicated extension  of  its  cavities,  is  situated  in  the  petrous  portion  of 
the  temporal  bone.  It  may  be  divided  into:  1.  The  vestibule  and 
semicircular  canals,  which  constitute  its  most  essential  parts  and  are 
present  in  all  vertebrate  animals ;  and  2.  The  cochlea,  winch,  in  man 
and  the  mammalia,  is  a  more  highly  developed  portion,  but  which  is 
absent  in  the  fishes  and  naked  reptiles,  and  only  partially  developed  in 
scaly  reptiles  and  in  birds. 

The  vestibule  (Fig.  150,  0  is  so  called  because  its  cavity  is  that  into 
which  the  fenestra  ovalis  immediately  opens,  and  which  leads  to  the 
semicircular  canals  and  cochlea.  It  has  an  ovoid  form,  and  presents, 
on  the  side  toward  the  tympanum,  two  openings,  namely :  1.  The 

*  Daguin,  Traite*  e*le"mentaire  de  Physique.     Paris,  1867,  tome  i.,  p.  596. 


THE    SENSES.  559 

fenestra  ovalis  C5),  corresponding  in  form  to  the  base  of  the  stapes, 
which  nearly  fills  it,  and  which  is  adherent  to  the  internal  periosteum 
of  the  labyrinth;  and  2.  The  fenes- 
tra rotunda  (6)  of  smaller  size  and 
closed  by  a  fibrous  membrane.  The 
posterior  portion  of  the  vestibule 
gives  origin  to  the  three  semicircu- 
lar canals,  namely :  1.  The  superior 
vertical  canal  (2)  with  its  plane 
lying  across  the  longitudinal  axis  of 
the  petrous  bone.  2.  The  inferior 
vertical  canal  (3)  the  plane  of  which 
is  parallel  with  the  median  surface 
of  the  petrous  bone :  and  3.  The 

,       .  1  /  \  -i    •  BONY  LABYRINTH  OP  THE  HUMAN  EAR,  twice 

horizontal    Canal  (4)  lying  acrOSS  the       the  natural  size.— 1.  Vestibule.    2.  Superior 
axis  Of  the    petrOUS    bone,  in  a   hori-       vertical  semicircular  canal.     3.  Inferior  ver- 
tical semicircular  canal.    4.  Horizontal  semi- 
ZOntal  plane.       Each  Semicircular  Ca-       circular  canal.    5.  Fenestra  ovalis.    6.  Fenes- 

nal  opens  into  the  vestibule  by  two     tra  rotunda-  7-  cochlea, 
orifices,  one  at  each  end ;  except  that  the  two  vertical  canals  unite  at 
one  extremity  into  an  orifice  common  to  both.     Each  canal  is  enlarged 
at  one  extremity,  where  it  joins  the  vestibule,  into  a  rounded  dilatation. 

This  part  of  the  bony  labyrinth  contains  a  colorless  fluid — the  peri- 
lymph,  and,  in  addition,  a  membranous  sac,  also  filled  with  fluid,  which, 
by  its  prolongations,  repeats  the  form  of  the  vestibule  and  semicircular 
canals.  This  sac,  with  its  extension  in  the  cochlea,  constitutes '  the 
membranous  labyrinth.  It  forms  the  most  important  part  of  the  in- 
ternal ear,  since  in  its  walls  the  filaments  of  the  auditory  nerve  have 
their  terminal  distribution. 

In  the  vestibule  the  membranous  sac  is  divided  into  two  parts  by  a 
transverse  partition.  One  of  these,  the  smaller  of  the  two,  is  the  sac- 
culus,  a  spherical  vesicle,  a  little  over  1.5  millimetre  in  diameter,  occu- 
pying the  anterior  and  inferior  portion  of  the  vestibule,  and  communi- 
cating by  a  narrow  canal  with  the  ductus  cochlearis  of  the  cochlea. 
The  other,  or  larger  sac,  is  the  utricle,  of  ellipsoid  form,  measuring 
3.5  millimetres  in  its  long  diameter.  The  utricle  and  the  membranous 
semicircular  canals  communicate  with  each  other  in  the  same  way  as 
the  bony  cavities  in  which  they  are  lodged ;  and  each  membranous 
canal  presents,  at  one  extremity,  a  rounded  dilatation,  known  as  the 
"  ampulla." 

The  membranous  sacs  and  canals  are  considerably  smaller  than  the 
osseous  cavities  which  contain  them,  and  occupy  nearly  everywhere 
an  eccentric  position,  being,  at  certain  points,  adherent  to  the  internal 
periosteum,  while  at  others  they  are  surrounded  by  the  perilymph. 
The  sacculus  and  utricle  together  occupy  about  two-thirds  of  the  cav- 
ity of  the  vestibule ;  and,  according  to  Rudinger,  are  so  placed  that 
neither  touches  the  base  of  the  stapes  at  the  fenestra  ovalis,  from  which 
they  are  separated  by  an  appreciable  layer  of  fluid.  Thus  sonorous  im- 


560  THE    NERVOUS    SYSTEM. 

pulses  reach  the  membranous  labyrinth,  not  directly  from  the  stapes, 
but  through  the  intermediate  vibration  of  the  perilymph. 

The  main  point  of  interest  in  regard  to  the  membranous  labyrinth 
relates  to  the  distribution  and  termination  of  the  auditory  nerve. 

The  auditory  nerve  sends  to  the  vestibule  two  branches ;  one  dis- 
tributed to  the  sacculus,  the  other  to  the  utricle  and  ampullae.  The 
mode  of  termination  of  the  nerve  fibres  in  both  divisions  is  essentially 
the  same.  They  are  not  distributed  generally  over  the  membrane,  but 
terminate  in  well-defined  spots,  characterized  by  a  thickening  of  the 
membranous  wall,  and  by  a  peculiar  form  of  epithelium  provided  with 
stiff,  pointed  cilia — the  so-called  auditory  hairs. 

In  the  sacculus  and  in  the  utricle,  the  terminal  nerve  spot,  or  "  mac- 
ula auditiva,"  is  an  oval  plate,  3  millimetres  by  1.5  in  the  sacculus, 
and  3  millimetres  by  2  in  the  utricle.  In  the  ampullae,  it  forms  a  trans- 
verse fold  of  the  membranous  wall,  projecting  inward  like  the  valvulae 
conniventes  of  the  small  intestine,  but  occupying  only  about  one-third 
of  their  circumference.  Elsewhere,  the  sacs  are  lined,  according  to 
Kolliker,  by  a  single  layer  of  pavement  epithelium  cells.  But  at  the 
spots  in  question  the  epithelium  is  twice  or  three  times  as  thick  as  in 
the  remaining  portions,  and  consists  of  elongated  cylindrical  and  fusi- 
form cells.  It  also  presents,  standing  upright  upon  its  surface,  the  cilia, 
or  auditory  hairs,  which  in  man  are  about  25  mmm.  in  length.  The 
terminal  fibres  of  the  auditory  nerve,  which  pass  toward  these  thick- 
ened spots,  may  be  traced,  according  to  all  recent  observers,  into  the 
epithelial  layer ;  and  certain  appearances  give  rise  to  the  supposition 
that  the  axis-cylinder  of  each  fibre  is  prolonged  through  a  fusiform 
epithelium  cell,  and  projects,  in  the  form  of  an  auditory  hair,  from  its 
free  extremity.  This  is  inferred  mainly  from  the  similarity  in  appear- 
ance between  the  axis-cylinder  of  the  nerve  fibres  and  the  slender 
downward  prolongation  of  the  fusiform  cells ;  and  from  the  fact  that 
both  structures  are  stained  blackish  or  jbrown  by  osmic  acid  (Riidinger). 
However  this  may  be,  there  is  no  doubt  that  the  projecting  cilia,  either 
mechanically  or  by  nervous  sensibility,  receive  and  transmit  the  sonor- 
ous vibrations  of  the  surrounding  fluid. 

A  remarkable  feature  connected  with  the  auditory  spots  of  the  sac- 
culus and  utricle  is  the  so-called  otoconia,  or  ear  sand.  This  consists 
of  calcareous  grains,  cm  bedded  in  a  gelatinous  material,  and  forming 
a  white,  chalky-looking  layer  immediately  over  the  auditory  spot.  The 
grains  are  rounded,  elongated,  or  prismatic  and  crystalline  in  form  ; 
the  largest  measuring,  according  to  Kolliker,  about  10  mmm.  in  length. 
Their  exact  office  is  unknown,  but  it  is  evident,  from  their  constant 
existence  in  this  situation  in  different  animals,  that  they  have  some 
important  relation  to  the  sense  of  hearing.  In  man,  mammalians, 
and  birds  they  arc  pulverulent.  In  reptiles  and  fish  they  are  some- 
times of  (Viable  concretions,  sometimes  rounded  masses,  hard  and  dense 
:i-  porcelain.  According  to  Wagner,  t  hey  are  completely  absent  onlv  in  the 
cyclostomi,  or  fishes  of  tin-  lowest  order,  including  the  lamprey  and  hag. 


THE    SENSES.  561 

Physiological  Action  of  the  Membranous  Labyrinth. — The  sacculus 
and  utricle  are  membranous  formations  suspended  in  the  fluid  of  the 
vestibule  and  supplied  by  fibres  of  the  auditory  nerve.  They  are  the 
essential  parts,  in  the  auditory  apparatus,  for  the  reception  of  sonorous 
impressions.  The  vibrations  of  the  atmosphere,  communicated  to  the 
membrana  tympani,  are  thence  transmitted  through  the  malleus,  incus, 
and  stapes.  From  the  base  of  the  stapes  they  pass  to  the  perilymph 
of  the  vestibular  cavity ;  thence,  through  the  wall  of  the  membranous 
sac,  to  the  endolymph  or  fluid  in  its  interior ;  and  the  vibration  of  thfs 
internal  fluid  acts  upon  the  nervous  terminations  at  the  auditory  spot. 
It  is  thus,  through  a  series  of  intermediate  vibrations,  that  sounds 
coming  from  without  finally  produce  their  impression  on  the  internal 
ear. 

Office  of  the  Semicircular  Canals. — These  singular  appendages 
have  attracted  special  attention,  owing  to  the  constancy  of  their  occur- 
rence and  the  peculiarity  of  their  position.  The  principal  features  of 
their  anatomical  history  are  the  following : 

1.  They  are  always  present,  as  portions  of  the  internal  ear,  in  mam- 
malians, birds,  and  reptiles,  and  nearly  always  in  fish ;  being  entirely 
absent  only  in  amphioxus,  where  there  is  no  organ  of  hearing  what- 
ever. • 

2.  They  are  always  three  in  number.     The  only  exception  to  this 
rule  is  found  among  fishes,  in  the  lamprey  and  the  hag ;  where  the 
entire  structural  development  is  very  incomplete.*     In  the  lamprey 
there  are  two,  and  in  the  hag  only  one,  the  cavity  of  which  is  con- 
founded with  that  of  the  utricle,  forming  a  ring-like  membranous  canal. 

3.  The  canals  stand  in  three  different  planes,  perpendicular  to  each 
other.    One  is  vertical  and  longitudinal,  in  relation  to  the  petrous  bone  ; 
another  vertical  and  transverse ;  and  the  third  transverse  and  horizon- 
tal.    They  represent  accordingly,  by  their  position,  the  three  dimen- 
sions of  space ;  and  from  this  circumstance  it  has  been  surmised  that 
they  serve  to  indicate  the  direction  from  which  sounds  are  perceived. 
But  subsequent  researches  have  yielded  nothing  to  corroborate  this 
view;    and   it  is  evident,  furthermore,  that,  from  whatever   quarter 
sounds  may  originally  come,  they  must  reach  the  internal  ear,  through 
the  membrana  tympani  and  chain  of  bones,  by  the  same  course. 

Lastly,  an  essential  point  in  the  structure  of  the  semicircular  canals 
is  that  they  are  destitute  of  nerve  fibres,  and  consequently  wanting 
in  sensibility.  The  only  nervous  distribution  connected  with  them  is 
that  to  the  ampullae  at  their  extremities,  but  no  fibres  extend  to  the 
canals  themselves.  Their  function  must  therefore  in  all  probability 
be  of  a  mechanical  or  physical  nature. 

In  experimenting  upon  the  internal  ear  in  animals,  it  has  been  re- 
marked that  division  or  injury  of  the  semicircular  canals  is  followed 

*  Owen,  Anatomy  of  the  Vertebrates.  London,  1868,  vol.  iii.,  p.  222.  Wagner, 
Comparative  Anatomy  of  the  Vertebrate  Animals,  Talk's  translation.  New  York, 
1845,  p.  227. 

2L 


562  THE    NERVOUS    SYSTEM. 

by  a  singular  affection  of  the  posture  and  voluntary  movements,  indi- 
cating disturbance  of  equilibrium.  These  phenomena  were  first  made 
known  by  Flourens  in  1825,*  and  have  been  witnessed  by  many  sub- 
.-eijiient  observers.  They  are  not  explained  by  all  in  the  same  way, 
but  there  is  little  discrepancy  in  regard  to  their  character  and  details. 
The  exposure  of  the  semicircular  canals  during  life  is  impracticable,  as 
a  rule,  in  the  mammalia,  owing  to  the  density  of  the  petrous  bone ; 
but  it  can  be  done  without  much  "difficulty  in  birds,  where  they  are 
sifrrounded  by  spongy  osseous  tissue.  The  pigeon  has  been  most  fre- 
quently used  for  this  purpose. 

The  most  striking  and  constant  effect  from  injury  of  the  semicircular 
canals  consists  of  abnormal  oscillatory  movements  of  the  head,  with 
imperfect  balancing  of  the  body.  These  phenomena  vary  according 
to  the  canal  which  has  been  divided.  If  it  be  a  vertical  canal,  the 
oscillation  of  the  head  is  upward  and  downward ;  if  it  be  a  horizontal 
one,  the  oscillations  are  from  left  to  right,  and  vice  versa.  If  the  cor- 
responding canal  on  both  sides  be  divided,  the  abnormal  movements 
are  more  rapid  and  continuous  than  if  the  injury  be  inflicted  on  one 
alone.  The  animal  is  still  capable  of  preserving  his  equilibrium  when 
at  rest ;  but  any  attempt  at  movement  brings  on  a  disordered  action, 
which  makes  walking,  running,  or  flying  difficult  or  hnpossible.  The 
most  simple  interpretation  of  these  results  is  that  the  animal  can  no 
longer  appreciate  the  position  of  the  head,  and  that  the  sense  of  equi- 
librium is  consequently  impaired  for  the  body  and  limbs. 

The  manner  in  which  the  semicircular  canals  may  contribute  to  the 
sense  of  equilibrium  is  as  follows :  If  a  goblet,  filled  with  water,  be 
turned  round  its  vertical  axis,  it  will  be  seen  that  the  water  does  not 
readily  turn  with  it ;  and  any  small  objects  suspended  in  it,  or  floating 
upon  its  surface,  will  remain  in  nearly  the  same  position,  while  the 
goblet  revolves  through  an  entire  circle.  The  adhesion  of  the  fluid  to 
the  glass  surfaces  is  not  sufficient  to  communicate  to  it  at  once  the 
motion  of  the  vessel.  Consequently  the  water  lags  behind  the  glass ; 
and  if  any  projecting  object. were  cemented  to  the  inside  of  the  goblet, 
so  as  to  turn  with  it,  it  would  be  subjected  to  a  backward  pressure, 
whenever  the  goblet  was  put  in  rotation. 

Somewhat  similar  conditions  arc  present  in  the  semicircular  canals. 
Whenever  the  head  is  rotated  from  side  to  side  in  a  horizontal  plane,  a 
momentary  increase  of  pressure  must  take  place  in  the  fluid  of  the 
horizontal  semicircular  canal  (Fig.  150, 4),  either  toward  or  from  the 
ampulla  at  one  end ;  and  this  increase  or  diminution  of  pressure  may 
be  perceptible  by  the  nervous  expansions  there  situated.  If  the  head 
be  moved  upward  or  downward,  a  corresponding  change  of  pressure 
will  take  place  in  the  inferior  vertical  canal  (Fig.  150, 3) ;  and  if  it  l>e 
inclined  laterally,  toward  the  right  or  left,  the  superior  vertical  canal 

*  RecluM-cli»-=  Mx|MTimrMt:iles  sur  les  Propri&&  et  Ie8  Fonctioiis  du  SystCme 
Nerveux,  2me  Edition.  Paris,  1842,  pp.  452,  454. 


THE    SENSES.  563 

(Fig.  150,  2),  will  experience  a  similar  variation.  Thus,  although  the 
membranous  semicircular  canals  be  not  themselves  sensitive  to  press- 
ure, they  may  serve  as  channels  for  conducting  an  impulse  to  the 
sensitive  organs  in  their  ampullae.  The  configuration  of  the  nervous 
expansions  in  the  ampulla  seems  especially  adapted  for  this  purpose, 
since  they  are  arranged  in  the  form  of  transverse  crescentic  folds. 
In  the  sacculus  and  utricle,  on  the  other  hand,  they  are  simply  flattened 
prominences  on  the  surface  of  the  membrane. 

If  it  be  asked,  why  an  apparatus  for  appreciating  equilibrium  should 
be  associated  with  the  organ  of  hearing,  it  may  be  remarked  that  in 
the  auditory  labyrinth  alone  there  are  sensitive  nerve  fibres  distributed 
to  an  epithelium  provided  with  hair  cells,  and  surrounded  by  a  watery 
fluid;  conditions  which  are  especially  suitable  for  the  perception  of 
variations  in  pressure,  and  consequently  for  that  of  changes  in  posi- 
tion. 

Cochlea.— The  cochlea,  so  named  from  its  resemblance  to  a  snail- 
shell,  is  a  spiral  bony  canal  making  two  or  three  turns  about  a  central 

FIG.  151. 


BONY  COCHLEA  OF  THE  HUMAN  EAR,  right  side ;  opened  from  its  anterior  face.    (Cruveilhier.) 

axis,  with  its  apex  directed  forward,  downward,  and  outward.  It  is" 
divided  longitudinally  by  a  thin,  bony  partition,  the  spiral  lamina, 
which  winds  round  its  axis,  following  the  spiral  turns,  but  presenting 
externally  a  free  border. 

From  this  border  a  fibrous  membrane,  the  membrana  basilaris, 
extends  outward  to  the  external  wall  of  the  cavity ;  thus  forming  two 
parallel  passages,  one  above  the  other.  The  upper  passage,  which 
communicates  at  its  base  with  the  vestibule,  is  the  scala  vestibuli. 
The  lower  reaches  to  the  fenestra  rotunda,  where  the  membrane, 
stretched  across  this  opening,  separates  its  cavity  from  that  of  the  tym- 
panum ;  it  is  accordingly  known  as  the  scala  tympani.  At  the  apex 
of  the  cochlea  a  minute  orifice  of  communication  between  the  two  canals 
has  been  described  by  some  writers,  and  doubted  by  others.  Accord- 


564  THE    NERVOUS    SYSTEM. 

ing  to  Buck,*  it  is  probable  that  no  such  opening  exists  in  the  natural 
condition  of  the  parts,  unless  it  be  microscopic  in  size.  But  whether 
the  canals  communicate  or  not  at  this  point,  the  partition  between  them 
is  partly  membranous  throughout;  and  by  this  means  any  increase  or 
diminution  of  pressure  at  the  fenestra  ovalis  will  be  transmitted,  through 
tin-  se.ila  vestilmli  and  scala  tympani,  to  the  membrane  of  the  fenestra 
rotunda.  This  provides  therefore  for  the  movement  of  the  stapes,  not- 
withstanding the  incompressible  nature  of  the  fluid  of  the  labyrinth. 

But  the  septum  formed  by  the  spiral  lamina  and  mcmbrana  basilaris 
is  not  the  only  longitudinal  partition  in  the  cochlea.  The  scala  vest  i- 
buli  is  also  divided  into  two  parallel  canals,  an  internal  and  an  external, 
by  a  thin  membranous  sheet,  which  starts  from  the  upper  surface  of  the 
spiral  lamina  near  its  outer  border,  and  extends  upward  and  outward 
to  the  external  wall  of  the  cochlear  cavity.  As  this  membrane  leaves 
the  spiral  lamina  at  an  angle  of  45  or  50  degrees,  it  shuts  off  from  the 
scala  vestibuli  a  separate  canal  of  prismatic  form,  having  for  its  floor 
the  membrana  basilaris,  for  its  outer  wall  the  wall  of  the  cochlea,  and 
for  its  upper  boundary  the  oblique  membranous  partition  above  de- 
scribed. This  canal  contains  the  auditory  epithelium  and  the  terminal 
fibres  of  the  auditory  nerve.  It  is  therefore  the  essential  part  of  the 
cochlea,  and  is  termed  the  ductus  cochlearis. 

The  ductus  cochlearis  terminates  at  its  apex  by  a  blind  extremity  ; 
but  at  its  base  it  communicates,  by  a  narrow  channel,  with  the  cavity 
of  the  sacculus.  It  is  consequently  an  extension  of  the  sacculus,  and 
part  of  the  membranous  labyrinth  ;  while  the  scala  vestibuli  belongs 
to  the  general  cavity  of  the  vestibule.  The  ductus  cochlearis  may  1>e 
considered  as  a  tubular  prolongation  of  the  sacculus,  rolled  upon  itself 
in  a  spiral  form,  and  held  in  position  by  the  adjacent  parts  of  the 
cochlea.  Like  the  rest  of  the  membranous  labyrinth,  it  is  filled  with 
a  watery  fluid,  and  surrounded  by  the  perilymph,  except  where  it  is 
adherent  to  the  walls  of  its  bony  cavity. 

Organ  of  Corti.  —  The  ductus  cochlearis  is  lined  with  pavement  epi- 
thelium, except  along  the  middle  of  the  membrana  basilaris.  Here 
there  is  a  continuous  elevated  ridge,  four  or  five  times  thicker  than  the 
epithelium  elsewhere,  consisting  of  enlarged  and  modified  epithelium 
cells,  and  containing  the  terminal  fibres  of  the  auditory  nerve.  This 
body  is  named  the  organ  of  Corti,"f  from  the  observer  by  whom  it  was 
first  described.  It  is  justly  considered  as  the  most  remarkable  structure 
in  the  internal  ear,  although  in  its  essential  features  analogous  to  the 
auditory  spots  of  the  sacculus  and  utricle. 

Tin-  organ  of  Corti  rests  upon  the  upper  surface  of  the  membrana 
basilaris.  Its  framework  consists  of  a  series  of  elongated,  rafter-like 
bodies,  arranged  in  two  rows,  internal  and  external.  These  bodies,  the 


*On  the  Mech.-mism  of  Hcuriim.  I'ri/.r  Kssay  of  the  Alumni  Association  of  the 
College  of  Physicians  and  Surgeons,  Now  York.  N<'tr  York  Medical  Journal,  June, 
1874. 

f  Zi-itschrift  fiir  \vi>smsrhaftlielie  Zoologie.     Leipzig,  1851,  Band  Hi.,  p.  109. 


THE    SENSES.  565 

inner  and  outer  "  fibres  of  Corti,"  are  separated  below,  where  they  rest 
upon  the  membrana  basilaris,  by  a  considerable  interval ;  but  their 
upper  extremities  lie  in  contact  with  each  other,  thus  forming  a  roof- 
like  connection,  the  "arch  of  Corti."  Near  the  arch,  the  epithelium 
cells  increase  in  length ;  and  at  its  inner  border  there  is  a  row  of  cells 
nearly  as  long  as  the  innermost  fibres  of  Corti,  and  in  a  similar  leaning 
position,  bearing  upon  their  upper  extremity  a  tuft  of  rigid  hairs  or 
cilia.  On  the  outer  border  of  the  arch  there  are  three  such  rows  of  hair 
cells ;  and  in  every  instance  the  cilia  project  through  openings  in  a  sort 

FIG.  152. 


U 

DIAGRAMMATIC  SECTION  OF  THE  ORGAN  OF  CORTI.— 1.  Membrana  basilaris.  2,  3.  Internal  and 
external  fibres  of  the  arch.  4.  Epithelium  cells  near  its  inner  and  outer  borders.  5.  Hair  cells 
lying  in  contact  with  the  arch.  Magnified  500  diameters. 

of  fenestrated  cuticle  extending  above  the  cells,  inward  and  outward, 
from  the  middle  of  the  arch. 

The  fibres  of  the  cochlear  branch  of  the  auditory  nerve  are  distributed 
to  the  organ  of  Corti.  The  bundles  forming  this  branch  penetrate  the 
base  of  the  cochlea,  and  thence  pass  upward,  through  its  axis,  diverging 
successively  in  a  horizontal  direction  between  the  two  layers  of  the 
spiral  lamina.  At  the  attached  border  of  the  lamina,  within  the  osseous 
canal,  there  is  a  linear  collection  of  bipolar  nerve  cells,  in  and  among 
which  the  fibres  pass,  and  with  many  of  which  they  are  connected. 
This  forms  the  "  spiral  ganglion  "  of  the  cochlear  nerve.  After  the 
fibres  have  passed  through  this  ganglion,  they  diverge  toward  the 
outer  border  of  the  spiral  lamina  and  the  membrana  basilaris.  At  this 
point  they  diminish  in  size  and  lose  their  medullary  layer ;  after  which 
they  penetrate  into  the  ductus  cochlearis,  and  reach  the  organ  of  Corti. 
In  this  organ  their  termination  in  the  epithelial  hair  cells  has  been 
most  positively  described  and  figured  by  Waldeyer.*  It  evidently 
represents,  in  the  ductus  cochlearis,  the  especial  apparatus  of  auditory 
sensibility. 

Physiological  Action  of  the  Cochlea. — The  cochlea,  no  doubt,  as  com- 
pared with  the  rest  of  the  internal  ear,  serves  for  the  precise  discrimi- 
nation of  minute  variations  in  sound.  Its  elongated  and  spiral  form, 
the  two  membranes  of  uniform  tension  which  inclose  the  ductus  coch- 
learis, and  the  multiple  rows  of  hair  cells  in  the  organ  of  Corti,  all 
indicate  its  capacity  for  the  distinct  perception  of  sonorous  impulses. 
Its  analogy  of  construction,  in  some  respects,  with  stringed  musical 
instruments,  has  induced  the  belief,  in  many  physiologists,  that  it  is  the 

*  Strieker's  Manual  of  Histology,  Buck's  edition.     New  York,  1872,  p.  1040. 


566  THE    NERVOUS    SYSTEM. 

organ  by  which  we  appreciate  the  pitch  of  musical  sounds.  According 
to  this  view,  the  radiating-  fibres  of  the  meinbrana  basilaris  are  attuned, 
by  their  length  and  tension,  to  different  notes  of  the  musical  scale  ;  and 
the  vibration  of  each  is  communicated  to  corresponding  hair  cells  in 
the  organ  of  Corti,  thus  reaching  the  terminal  fibres  of  the  auditory 
nerve.  For  every  note  which  gains  admission  to  the  internal  ear,  only 
certain  fibres  and  hair  cells  of  the  ductus  cochlearis  are  thrown  into 
vibration,  and  only  certain  fibres  of  the  cochlear  nerve  receive  a  sono- 
rous impression.  There  is  certainly  an  apparent  similarity  between 
the  fibrous  and  cellular  elements  in  the  organ  of  Corti  and  the  ranges 
of  strings,  capable  of  vibrating  to  different  notes,  in  a  harp  or  piano- 
forte ;  and  the  similarity  is  sufficient  to  suggest  a  corresponding  action 
in  the  two  cases. 

But  the  difficulty  in  attributing  to  the  cochlea  the  discrimination  of 
musical  notes,  lies  in  the  fact  that  its  development  in  different  animals 
does  not  correspond  with  their  capacity  for  the  production  and  percep- 
tion of  musical  sounds.  The  cochlea,  under  the  form  which  it  presents 
in  man,  is  confined  to  the  mammalia.  In  birds  this  part  of  the  audi- 
tory apparatus  is  an  obtusely  conical  eminence,*  containing  two  small 
cartilaginous  cylinders  united  by  a  membrane  representing  the  meni- 
brana  basilaris ;  and  the  part  corresponding  with  the  organ  of  Corti 
contains  only  nerve  terminations  and  hair  cells  somewhat  resembling 
those  of  the  inner  row  in  mammalia ;  the  arch  of  Corti,  and  the  three 
outer  rows  of  hair  cells,  with  their  cuticular  covering,  being  absent. 
In  serpents  and  lizards,  the  cochlea  is  similar  to  that  of  birds ;  while 
in  the  naked  reptiles  and  in  fishes  it  is  completely  undeveloped. 

Thus,  in  all  the  mammalia,  the  cochlea  is  an  important  part  of  the 
internal  ear,  but  little  inferior  to  the  same  organ  in  man.  But  in  sing- 
ing birds  it  is  comparatively  rudimentary.  Some  of  these  birds  may 
be  taught  to  repeat  particular  melodies,  showing  that  their  capacity 
of  discriminating  musical  notes  is  equal  to  their  power  of  producing 
them  by  the  vocal  organs.  And  yet  that  part  of  their  auditory  appa- 
ratus which  should  be  most  highly  developed  according  to  the  view  in 
question,  is  in  reality  the  least  so.  If  we  compare  a  horse  or  a  pig  with 
a  thrush  or  a  mocking-bird,  it  is  evident  that  the  grade  of  musical  sen- 
sibility in  these  animals  is  in  no  relation  with  the  development  of  the 
cochba.  In  fact,  the  cochlea  of  a  singing  bird  resembles  that  of  a  croco- 
dile or  a  serpent  more  closely  than  that  of  a  quadruped  or  a  man.  At 
the  same  time,  the  other  parts  of  the  internal  ear  in  birds,  the  double 
sac  of  the  vestibular  cavity,  the  membranous  semicircular  canals  and 
ampullae,  the  fenestra  ovalis,  and  the  fenestra  rotunda,  are  all  highly 
developed ;  some  of  them  nearly  or  quite  as  much  so  as  in  mammalia  n>. 


*  Owen,  Anatomy  of  the  Vertebrates.  London,  1866,  vol.  ii.,  p.  134. 
Comparative  Anatomy  of  the  Vertebrate  Animals,  Tulk's  Translation.  New  York, 
1*1~».  j».  \^.  Wal.K-yer,  in  Strieker's  Manual  of  Histology,  Buck's  Edition.  New 
York,  1872,  p.  1046. 


THE    SENSES.  567 

This  throws  a  doubt  on  the  special  office  of  the  cochlea  in  auditory 
sensations. 

Persistence  of  Sonorous  Impressions  and  the  Production  of  Musical 
Sounds. — The  effect  produced  by  a  sonorous  vibration  continues  for  a 
short  time  after  the  cessation  of  its  cause.  Usually  the  interval  between 
two  different  impulses  is  sufficient  to  allow  the  first  impression  to  dis- 
appear before  the  second  is  received,  and  the  ear  distinguishes  them  in 
succession.  But  if  they  follow  each  other  at  equal  intervals,  with  a 
certain  rapidity,  they  produce  the  impression  of  a  continuous  sound ; 
and  this  sound  has  a  higher  or  lower  pitch,  according  to  the  rapidity 
of  its  vibrations.  The  numerical  relation  of  musical  notes  thus  pro- 
duced has  been  studied  by  various  means.  One  of  these  is  the  siren 
of  Savart,  in  which  successive  puffs  of  air  are  emitted  through  small 
openings,  with  a  rapidity  which  can  be  varied  at  will  and  registered 
by  an  automatic  index.  In  another  method  the  shocks  are  given  by 
the  points  of  a  toothed  wheel  turning  with  known  velocity  against  the 
projecting  edge  of  a  card.  The  number  of  vibrations  corresponding 
to  a  particular  note  may  also  be  registered  by  attaching  to  the  extrem- 
ity of  a  tuning-fork,  a  light  stilet  which  traces  upon  the  surface  of  a 
revolving  cylinder,  an  undulating  line  (Fig.  96,  a) ;  the  number  of  un- 
dulations in  a  given  space  indicating  the  frequency  of  vibration  of  the 
tuning-fork.  A  simple  vibration  represents  the  movement  in  one  direc- 
tion ;  a  double  vibration  is  the  complete  to-and-fro  oscillation,  which 
brings  the  moving  point  back  to  its  original  position. 

By  this  means  it  is  found  that  sonorous  impulses,  following  each 
other  with  a  rapidity  of  less  than  sixteen  times  per  second,  are  sepa- 
rately distinguishable ;  but  above  that  frequency  they  are  merged  into 
a  continuous  sensation.  When  the  shocks  are  repeated  at  irregular 
intervals,  the  only  characters  perceptible  in  the  sound  are  its  intensity 
and  quality.  But  if  they  succeed  each  other  at  regular  intervals,  the 
sound  produced  has  a  position  in  the  musical  scale,  as  a  high  or  low 
note.  The  more  frequent  the  repetitions,  the  higher  the  note ;  but  a 
limit  is  at  last  reached  at  which  the  ear  fails  to  perceive  the  sound, 
and  an  excessively  high  note  is  therefore  inaudible.  This  is  probably 
due  to  the  following  reason  :  A  sonorous  vibration,  to  be  perceptible, 
must  have  a  certain  extent  or  amplitude ;  that  is,  the  particles  of  the 
vibrating  body  must  move  to  and  fro,  at  each  impulse,  for  a  certain 
distance  in  space.  The  intensity  of  a  sonorous  impression,  accordingly, 
depends  on  the  amplitude  of  the  vibrations,  while  its  pitch  or  tone 
depends  on  their  frequency.  But  the  more  frequently  a  body  vibrates 
in  a  triven  time,  the  less  extensive  must  be  its  movements,  if  their 
velocity  remain  the  same.  Consequently,  when  these  vibrations  arrive 
at  a  certain  frequency,  unless  their  velocity  be  increased  in  proportion, 
their  amplitude  becomes  so  small  that  they  make  no  impression  on  the 
ear,  and  they  are  therefore  inaudible. 

It  is  evident,  however,  that  such  a  sound  would  be  perceptible  if  the 
sensibility  of  the  auditory  apparatus  were  increased  to  the  requisite 


568  THE    NERVOUS    SYSTEM. 

degree ;  and  it  is  supposed  that  certain  insects  may  be  capable  of  per- 
ceiving sounds  of  very  high  pitch  which  are  inaudible  to  the  human 
ear.  To  an  organ  of  such  acute  sensibility  a  very  low  note,  on  the 
other  hand,  would  appear  as  a  succession  of  distinct  impulses. 

The  limits  of  frequency,  within  which  sonorous  vibrations  are  per- 
ceptible to  man  as  musical  sounds,  are  16  double  vibrations  per  second 
for  the  lowest  notes,  and  38,000  for  the  highest.  But,  according  to 
Wundt,  the  exact  discrimination  of  musical  pitch  is  confined  within 
much  narrower  limits,  especially  for  the  higher  notes. 

Duration  of  a  Sound  required  for  Sonorous  Impressions. — This 
point  has  been  investigated  by  Savart*  in  the  following  manner:  He 
ascertained,  by  experiment,  that  the  ear  could  appreciate  the  pitch  of  a 
sound  made  by  a  toothed  wheel  revolving  at  the  rate  of  10,000  shocks 
per  second.  By  successively  removing  the  teeth  from  different  portions 
of  its  circumference,  he  diminished  in  a  corresponding  degree  the  time 
during  wThich  the  shocks  were  produced;  and  he  found  that  such  a  wheel 
would  give  a  sound  of  definite  pitch  with  only  two  teeth  adjacent 
remaining.  The  double  shock  thus  produced  would  occupy  only  ^/^ 
of  a  second ;  and  this  duration  of  impulses  was  sufficient  to  make  upon 
the  ear  a  distinct  musical  impression. 

*  Daguin,  Traite"  ElSmentaire  de  Physique.     Paris,  1869,  tome  i.,  p.  517. 


SECTION  IY. 

EEPRODUCTION. 


CHAPTER    I. 

THE  NATUEE  OF  EEPRODUCTION  AND   THE  0  BIG  IN 
OF  PLANTS  AND  ANIMALS. 

T)  EPRODUCTION  is  the  process  by  which  the  different  kinds  of 
-lAj  organized  beings  are  perpetuated,  notwithstanding  the  limited 
existence  of  each  individual.  It  includes  the  production,  growth,  and 
development  of  new  germs,  as  well  as  the  history  of  successive  changes 
in  the  organs  and  functions,  and  the  modifications  of  external  form  at 
different  periods  of  life. 

All  organized  bodies  pass  through  various  stages  of  development, 
in  which  their  structure  and  functions  undergo  corresponding  altera- 
tions. The  changes  of  nutrition  and  growth,  by  which  the  animal 
or  plant  is  distinguished,  correspond  in  activity  wTith  its  other  vital 
phenomena ;  since  these  phenomena  depend  on  the  continuance  of  the 
nutritive  process.  Thus  the  organs  and  tissues  are  the  seat  of  a  double 
change  of  renovation  and  decay,  but  retain  nevertheless  their  original 
constitution,  and  continue  to  exhibit  their  vital  phenomena. 

This  change,  however,  is  not  the  only  one  which  takes  place.  Al- 
though the  bodily  structure  Appears  to  be  maintained  by  the  nutritive 
process  from  one  moment  to  another,  or  from  day  to  day,  yet  examina- 
tion at  longer  intervals  will  show  that  this  is  not  precisely  the  case ; 
since  the  changes  of  nutrition  are  progressive  as  well  as  momentary. 
The  composition  and  structure  of  the  bones  are  not  the  same  at  the 
age  of  twenty-five  years  that  they  were  at  fifteen.  At  the  later  period 
they  contain  more  calcareous  and  less  organic  matter  than  before  ;  their 
solidity  being  consequently  increased,  while  their  elasticity  is  dimin- 
ished. There  is  a  notable  difference  in  the  quantities  of  oxygen  and 
carbonic  acid  inspired  and  exhaled  at  different  ages  ;  and  the  irritabil- 
ity of  the  muscles  is  diminished  after  some  years,  owing  to  a  slow,  but 
steady  and  permanent,  deviation  in  their  intimate  constitution. 

The  vital  properties  of  the  organs,  therefore,  change  with  their  vary- 
ing structure ;  and  a  time  comes  at  last  when  they  are  perceptibly  less 
capable  of  action  than  before.  The  very  exercise  of  the  vital  powers 
is  inseparably  connected  with  the  alteration  of  the  organs  to  which 

569 


570  REPRODUCTION. 

they  belong;  and  the  functions  of  life,  instead  of  remaining  indefi- 
nitely the  same,  pass  through  a  series  of  changes,  which  finally  termi- 
nate in  their  complete  cessation. 

The  history  of  an  animal  or  plant  is,  therefore,  a  history  of  suc- 
cessive epochs  or  phases  of  existence,  in  each  of  which  its  structure 
and  functions  differ  more  or  less  from  those  in  every  other.  The 
organized  being  has  a  definite  term  of  life,  through  which  it  p; 
according  to  an  invariable  law,  and  which,  at  some  regularly  appointed 
time,  comes  to  an  end.  The  plant  germinates,  grows,  blossoms,  bears 
fruit,  withers,  and  decays.  The  animal  is  born,  nourished,  and  brought 
to  maturity,  after  which  he  retrogrades  and  dies.  The  very  commence- 
ment of  existence,  by  leading  through  its  successive  intermediate  stages, 
conducts  at  last  necessarily  to  its  termination. 

But  while  individual  organisms  are  constantly  perishing  and  disap- 
pearing from  the  stage,  the  particular  kind,  or  species,  remains  in  exist- 
ence, without  any  important  change  in  the  forms  belonging  to  it.  The 
horse  and  the  ox,  the  oak  and  the  pine,  the  numerous  wild  and  domes- 
ticated animals,  as  well  as  the  different  races  of  mankind,  have  remained 
without  essential  alteration  since  the  earliest  historical  epochs.  Yet 
during  this  period  innumerable  individuals,  of  each  species  or  race, 
have  lived  through  their  natural  term  and  successively  passed  out  of 
existence.  A  species  may  therefore  be  regarded  as  a  type  or  class  of 
organized  beings,  in  which  the  individuals  composing  it  die  off  and 
disappear,  but  which  nevertheless  repeats  itself  from  year  to  year,  and 
maintains  its  ranks  constantly  full  by  the  continued  accession  of  other 
similar  forms.  This  process,  by  which  new  organisms  make  their 
appearance,  in  place  of  those  which  are  destroyed,  is  the  process  of 
reproduction.  The  first  important  topic,  in  the  study  of  reproduction, 
is  that  of  the  conditions  necessary  for  its  accomplishment. 

Reproduction  by  Generation. 

It  is  well  known  that,  in  the  reproduction  of  animals  or  plants,  the 
young  organisms  are  produced,  as  a  rule,  from  the  bodies  of  the  elder. 
The  relation  between  the  two  is  that  of  parents  and  progeny.  The 
progeny,  accordingly,  owes  its  existence  to  an  act  of  generation  ;  and 
the  new  organisms,  thus  generated,  become  in  turn  the  parents  of 
others  which  succeed  them.  For  this  reason,  wherever  such  plan, 
animals  exist,  they  indicate  the  preceding  existence  of  the  same  species  ; 
and  if  by  any  accident  the  whole  species  should  be  destroyed  in  any 
particular  locality,  no  new  individuals  could  be  produced  there,  unless 
by  the  importation  of  others  of  the  same  kind. 

The  most  prominent  feature  of  generation,  as  a  natural  phenomenon, 
is  that  the  young  animals  or  plants  thus  formed  are  of  the  same  I 
with  their  parents.  They  reproduce  the  specific  characters  by  which 
their  predecessors  were  distinguished;  and  this  takes  place  by  a  law 
so  universal  that  it  seems  almost  a  truism  to  state  it.  But  this  is  only 
because  it  has  been  so  constantly  a  matter  of  observation,  that  in 


THE  NATURE  OF  REPRODUCTION.         571 

popular  experience  it  appears  a  natural  necessity.  In  reality  it  is  one 
of  the  most  remarkable  phenomena  connected  with  the  generative 
process;  and  it  indicates  an  unbroken  connection  of  physiological  acts, 
extending  through  the  lives  of  many  different  individuals.  Thus  we 
know  that  the  progeny  of  a  fox  will  always  be  foxes ;  and  that  if  we 
sow  oats,  it  will  be  a  crop  of  oats  that  is  produced  in  consequence. 
Generation,  accordingly,  not  only  gives  rise  to  new  animals  or  plants, 
but  it  serves  to  continue  indefinitely  the  existence  of  the  species,  with 
its  characteristic  marks  and  qualities. 

Our  idea,  therefore,  of  a  species  includes  two  different  elements,  one 
of  which  is  anatomical,  the  other  physiological.  Its  anatomical  char- 
acter is  the  similarity  of  form,  size,  and  structure  between  the  individ- 
uals .  belonging  to  it,  which  we  recognize  at  a  glance ;  its  physiological 
character  is  the  fact,  established  by  experience,  that  it  will  reproduce 
itself,  and  thus  remain  distinct  through  an  indefinite  series  of  succes- 
sive generations. 

It  is  not  possible  to  say  that  the  anatomical  'characters  of  a  species 
have  been  absolutely  the  same  throughout  all  previous  time,  or  that 
they  will  remain  so  without  limit  in  future.  The  fossil  remains  of 
animals  and  plants,  differing  from  those  now  in  existence,  show  that 
species  are  not  persistent  and  invariable  through  very  long  periods ; 
and  that  they  may  either  become  so  modified  as  to  present  a  different 
appearance,  or  may  entirely  come  to  an  end,  like  the  extinct  mastodons 
and  horses  of  the  United  States,  and  be  replaced  by  others  from  a  dif- 
ferent locality.  But  in  whatever  way  we  may  explain  the  geological 
succession  of  different  species,  it  is  certain  that  at  any  one  time  their 
essential  characters  are  those  above  described ;  and  that  each  species, 
by  the  process  of  generative  reproduction,  remains  distinct  from  the 
others  which  are  contemporary  with  it. 

But  the  production  of  young  animals,  similar  to  their  parents,  although 
the  final  result  of  the  generative  process,  is  never  immediate.  The 
young  progeny  is  at  first  different  from  its  parents,  and  only  comes 
to  resemble  them  through  a  series  of  changes,  often  very  remarkable  in 
kind.  The  embryo  of  a  vertebrate  animal,  though  incomplete  in  struc- 
ture, presents  some  analogy  of  form  with  the  adult.  But  in  many 
invertebrates,  the  young,  even  when  hatched  and  capable  of  active 
locomotion,  are  so  different  from  their  parents  that  they  would  never 
be  referred  to  the  same  species,  unless  their  identity  were  demonstrated 
by  subsequent  development.  The  young  mosquito  is  a  wingless  crea- 
ture living  beneath  the  surface  of  stagnant  pools ;  and  the  eggs  of  the 
butterfly,  when  hatched,  give  birth  not  to  butterflies  but  to  caterpillars. 
The  caterpillars,  however,  are  not  creatures  of  another  species,  but 
young  butterflies ;  and  they  become  similar  to  their  parents  after  cer- 
tain changes,  which  take  place  at  definite  periods  of  their  development. 

The  reproduction  of  form,  therefore,  which  marks  a  species,  is  accom- 
plished through  a  series  of  changes  in  regular  order ;  and  this  series, 
taken  together,  may  be  represented  by  a  circuit,  which  starts  from  the 


572  REPRODUCTION. 

egg,  is  continued  through  successive  phases  of  growth,  transformation 
and  maturity,  and  terminates  at  last  with  the  production  of  an  ego-. 
As  this  egg  is  similar  to  the  first,  the  changes  repeat  themselves  in  their 
previous  order,  and  the  indefinite  continuance  of  the  species  is  thus 
established. 

tf/Htnlaneous  Generation. — The  commonest  observation  shows  that 
the  above  facts  hold  good  in  regard  to  all  animals  and  plants  with 
whose  history  we  are  fully  acquainted.  But  it  has  sometimes  been 
surmised  that  there  are  exceptions  to  this  rule ;  and  that  living  beings 
may,  under  certain  circumstances,  be  produced  from  inanimate  mate- 
rials ;  thus  presenting  the  singular  phenomenon  of  a  progeny  without 
parents.  Such  a  production  of  organized  bodies  is  known  as  sponta- 
neous generation.  Its  existence  is  doubted  by  most  physiologists,  and 
has  never  been  positively  established  for  any  particular  species ;  but  it 
has  been  at  various  times  the  subject  of  discussion,  forming  a  some- 
what remarkable  chapter  in  the  history  of  physiology. 

It  may  be  remarked'  in  general  that  the  organisms,  supposed  capable 
of  originating  by  spontaneous  generation,  have  been  always  those 
whose  natural  history  was  obscure,  owing  either  to  their  minute  size 
or  to  certain  physiological  peculiarities.  Wherever  animals  or  plants 
appeared  in  abundance  without  evidence  of  the  source  from  which  they 
came,  it  was  formerly  conjectured,  for  that  reason,  that  their  produc- 
tion was  spontaneous;  and  the  ancient  naturalists  supposed  all  ani- 
mals, except  those  which  visibly  lay  eggs  or  produce  living  young,  to 
be  formed  by  the  fortuitous  combination  of  their  organic  ingredients. 
Maggots,  shell  fish,  grubs,  worms,  and  even  some  fishes  were  thought 
to  be  produced  in  this  way,  because  they  had  no  apparent  specific  origin. 

But  further  observation  showed  that  these  animals  were  really  pro- 
duced by  generation  from  parents ;  their  secret  methods  of  propa- 
gation being  discovered,  and  their  relationship  being  detected  by  fol- 
lowing the  development  of  the  young.  A  frequent  obstacle  to  the 
identification  of  species,  in  these  investigations,  is  the  interval  which 
elapses  between  the  laying  of  the  eggs  and  the  subsequent  appearance 
of  the  young  brood ;  the  new  generation  not  showing  itself  until  the 
former  has  disappeared.  A  striking  instance  is  that  of  the  seventeen- 
year  locust  (Cicada  septendecim} ,  where  a  period  of  seventeen  years 
intervenes  between  the  hatching  of  the  larva  and  the  appearance  of  the 
perfect  insect;  the  larva  all  this  time  remaining  buried  in  the  ground, 
while  the  lite  of  the  perfect  insect  does  not  last  over  six  weeks.  But 
notwithstanding  this  difficulty,  most  of  these  cases  were  gradually 
traced  to  the  usual  method  of  generation  from  parents. 

Another  source  of  error  is  the  dissimilarity  sometimes  existing 
between  parents  and  young,  especially  when  accompanied  by  a  differ- 
ence in  their  habits  of  life.  Tntil  the  middle  of  the  seventeenth  century 
then-  was  no  more  undoubted  instance  of  spontaneous  generation  than 
the  a p] >e;i ranee  of  maggots  in  putrefying  flesh.  These  creatures  always 
show  tin -n, selves  in  meat  at  a  certain  stage  of  its  decomposition;  they 


THE    NATURE    OF    REPRODUCTION.  573 

are  never  seen  elsewhere ;  and  they  do  not  apparently  possess  the 
power  of  producing  young.  For  these  reasons  they  were  believed  to 
originate  from  the  dead  flesh  and  to  die  without  leaving  a  progeny. 
But  the  experiments  of  Redi  in  1668,  demonstrated  the  fallacy  of  this 
opinion  and  the  true  origin  of  the  maggots.  He  took,  in  the  month 
of  July,  eight  wide-mouthed  bottles  and  placed  in  them  pieces  of  flesh. 
Four  of  the  bottles  were  left  open  to  the  atmosphere,  while  the  remain- 
ing four  were  closed  by  paper  fastened  over  their  orifices.  In  a  short 
time  the  flesh  in  the  uncovered  bottles  was  filled  with  maggots,  a  pecu- 
liar kind  of  fly  meanwhile  passing  in  and  out  by  the  open  mouth ;  but 
in  the  closed  bottles  not  a  maggot  was  visible,  even  after  several 
months. 

Thus  it  was  evident  that  the  maggots  were  not  formed  from  the  dead 
flesh,  but  that  their  germs  came  in  some  way  from  without ;  and  con- 
tinued observation  showed  that  they  were  hatched  from  eggs  deposited 
by  the  flies,  and  that  after  a  time  they  became  perfect  insects  similar 
to  their  parents.  An  extension  of  these  observations  to  other  inver- 
tebrate animals  made  known  a  great  variety  of  instances  in  which  the 
connection  of  parents  and  progeny  might  be  traced  through  several 
intermediate  conditions  ;  so  that  apparent  differences  in  their  configura- 
tion and  structure  no  longer  offered  a  serious  difficulty  to  the  investi- 
gator. As  a  general  rule,  since  that  time,  whenever  a  rare  or  compara- 
tively unknown  animal  or  plant  has  been  suspected  to  originate  by 
spontaneous  generation,  it  has  only  been  necessary  to  examine  thor- 
oughly its  habits  and  functions,  to  discover  its  real  methods  of  propa- 
gation, and  to  show  that  they  correspond,  in  all  essential  particulars, 
with  the  ordinary  laws  of  reproduction.  The  limits  within  which  the 
doctrine  of  spontaneous  generation  could  be  applied  have  been  thus 
gradually  narrowed,  in  the  same  degree  that  the  study  of  natural  his- 
tory has  advanced ;  the  presumption  of  its  existence  always  hanging 
upon  the  outskirts  of  definite  knowledge,  and  relating  only  to  those 
animals  or  plants  which  are  for  the  time  imperfectly  understood.  The 
two  groups  from  which  it  has  been  most  recently  excluded  are  the 
Entozoa  and  the  Infusoria. 

I.  Entozoa. — These  are  parasitic  organisms  inhabiting  the  bodies  of 
other  living  animals,  from  whose  organic  juices  they  derive  their  nour- 
ishment. 

There  are  many  kinds  of  entozoa,  all  of  which  are  confined,  more  or 
less  strictly,  to  certain  parts  of  the  body  which  they  inhabit.  They 
are  found  in  the  intestines,  the  liver,  the  kidneys,  the  lungs,  the  heart, 
and  the  blood-vessels ;  some  on  the  surface  of  the  brain ;  others  in  the 
muscles  or  in  the  eyeball.  Each  parasite,  as  a  rule,  is  peculiar  to 
the  species  of  animal  which  it  inhabits,  and  to  a  particular  part  of  the 
body,  or  even  to  a  part  of  one  organ.  Thus,  Ascaris  lumbricoides 
is  found  in  the  small  intestine,  Oxyuris  vermicularis  in  the  rectum, 
Trichocephalus  dispar  in  the  ca3cum.  One  kind  of  Distorna  has  its 


574  REPRODUCTION. 

place  in  the  lungs  of  the  green  frog,  another  in  those  of  the  brown 
frog.  Cysticercus  cellulose  is  found  in  the  connective  tissue  ;  Trichina 
spiralis  in  the  substance  of  the  muscles. 

With  regard  to  many  of  these  parasites  the  only  difficulty  in  account- 
ing for  their  existence,  otherwise  than  by  spontaneous  generation,  lay 
in  their  being  confined  to  such  narrow  limits.  It  seemed  probable  that 
some  local  conditions  must  be  requisite  for  the  production  of  a  parasite, 
which  was  only  to  be  found  in  the  biliary  passages,  the  kidneys,  or  the 
lungs  of  a  living  animal.  A  little  consideration,  however,  makes  it 
evident  that  these  conditions  are  neither  necessary  nor  sufficient  for 
the  production  of  such  a  parasite,  but  only  for  its  development  and 
nutrition.  Most  internal  parasites  reproduce  their  species  by  genera- 
tion. They  have  male  and  female  organs,  and  produce  fertile  eggs, 
often  in  great  abundance.  The  eggs  in  a  single  female  Ascaris  are  to 
be  counted  by  thousands ;  and  those  in  a  tapeworm  by  millions.  In 
order  that  these  eggs  may  be  hatched,  and  their  embryos  developed, 
certain  conditions  are  requisite ;  as  the  seeds  of  plants  need,  for  their 
germination  and  growth,  an  appropriate  soil  and  a  certain  degree  of 
warmth  and  moisture.  It  is  no  more  remarkable  that  Oxyuris  vermi- 
cularis  should  inhabit  the  rectum,  and  Ascaris  lumbricoides  the  ileum, 
than  that  Lobelia  inflata  should  grow  only  in  dry  pastures,  and  Lobelia 
cardinalis  by  the  side  of  running  brooks.  The  lichens  flourish  on  the 
exposed  surfaces  of  rocks  and  stone  walls ;  while  the  fungi  vegetate  in 
darkness  and  moisture,  on  the  decaying  trunks  of  dead  trees.  Yet  all 
these  plants  are  reproduced  by  generation,  from  germs  which  require 
special  conditions  for  their  growth  and  development.  If  any  animal 
or  vegetable  germ  be  deposited  in  a  locality  where  the  requisite  condi- 
tions are  present,  it  is  developed  and  comes  to  maturity ;  otherwise 
not.  Thus  the  internal  parasites,  like  other  living  organisms,  are  con- 
fined to  certain  situations  by  the  necessities  of  their  nourishment  and 
growth. 

But  in  some  instances  there  are  two  further  difficulties.  First,  the 
parasites  in  question  do  not  inhabit  the  open  passages  or  canals  of 
the  body,  but  lie  encysted,  in  the  solid  substance  of  the  tissues,  with- 
out visible  means  of  access  from  the  exterior.  Secondly,  they  are  sex- 
less ;  and,  if  they  perform  no  generative  function,  it  does  not  readily 
appear  how  they  can  themselves  have  beei  derived  from  parents.  The 
two  kinds  of  entozoa,  in  which  these  peculiarities  are  most  strongly 
marked,  and  in  which  they  have  been  must  fully  explained,  are  Cysti- 
cercus cellulose  and  Trichina  spiralis. 

1.  Cysticercus  cellulosse. — This  is  a  bladder-shaped  parasite  of  some- 
what flattened  form,  about  10  millimetres  in  diameter,  found  in  the  sub- 
cutaneous and  interniuscular  connective  tissue  of  the  piir,  whore  it 
appears  under  the  form  of  whitish  specks,  iz-iving  rise  to  the  appearance 
known  ;>s  "measly  pork."  Each  parasite  is  enveloped  in  a  cyst,  but 
the  bladder-like  body,  when  extracted,  exhibits  at  one  spot  a  minute 


THE    NATURE    OF     REPRODUCTION.  575 

depression  or  involution  of  its  wall.     From  this  point  a  slender  neck, 

ending  in  a  rounded  head,  may  be  extruded  by  pressure ;  after  which 

the  animal  is  seen  to  consist  of  a  head  and  neck,  terminated  posteriorly 

by  a  dilated,   sac-like   tail,   whence    its 

generic  name  of  cysticercus.    Its  specific  FIG.  153. 

name  is  derived  from  its  inhabiting  the 

connective    tissue,   formerly   known   as 

the  "cellular  tissue."     The  head  of  the 

parasite,  when  magnified,  shows  upon 

its  surface  four  sucking  disks,  and  near 

its  extremity  a  double  crown  of  curved 

Calcareous    processes    Or    hooks.       There    CYSTICERCUS  CELLULOSE,  from  the  flesh 

are  no  distinguishable  internal  organs,     «tttttZ2E*t 

and    the    Caudal  Vesicle    Contains  Only  an       traded.    2,  3.  The  same,  with  head  and 

albuminous    fluid.      Thus   there   is   no 
other  apparent  source  for  these  organ- 
isms than  the  tissues  which  they  inhabit,  nor  have  they  any  visible 
mode  of  continuing  their  species  by  generation. 

But  it  has  been  shown  by  Yan  Beneden,  Leuckart,  Haubner,  and 
Kiichenmeister,*  that  Cysticercus  cellulosae  is  the  embryonic  progeny 
of  Ta3nia  soliuin,  or  the  solitary  tapeworm,  found  in  the  small  intestine 
of  man.  The  specific  identity  of  the  two  was  first  suspected  from  the 
similarity  of  the  head,  which  presents  the  same  sucking  disks  and 
crown  of  hooks  in  Ta3nia  as  in  Cysticercus.  But  in  Taenia  the  neck, 
instead  of  terminating  in  a  vesicular  appendage,  is  elongated  and 
wrinkled.  The  wrinkles,  after  a  certain  distance,  become  deepened  into 
superficial  furrows,  marking  off  the  body  into  oblong  articulations,  each 
articulation  showing  a  double  system  of  communicating  vascular  canals, 
and  distinctly-marked  generative  organs  of  both  sexes.  As  they  recede 
by  successive  growth  farther  from  the  head,  the  generative  organs  be- 
come more  complete,  and  are  at  last  filled  with  mature  fecundated  eggs, 
in  which  the  embryos  are  already  partially  developed.  The  tapeworm 
then  forms  a  chain  or  colony  of  articulations,  sometimes  from  six  to 
eight  metres  in  length,  attached  to  the  mucous  membrane  of  the  in- 
testine by  the  minute  head  at  its  anterior  extremity. 

By  the  experiments  above  mentioned  it  was  found  :  1st.  That  mature 
articulations  from  the  taania  solium  of  man,  if  administered  to  young 
pigs  with  their  food,  produce  a  brood  of  cysticercus  cellulosae  in  the 
flesh  of  these  animals ;  and,  2d.  That  cysticercus  cellulose  from  measly 
pork,  if  swallowed  by  man,  becomes  developed  in  the  intestine,  within 
a  few  days,  into  ribbon-like  worms,  recognizable  as  young  specimens 
of  taania  solium. 

The  manner  in  which  the  pig  becomes  infested  with  cysticercus  is 
as  follows :  In  the  fully-formed  tapeworm,  in  the  human  intestine,  the 
mature  articulations  separate  from  the  rest  of  the  colony,  and  either 

*  Animal  and  Vegetable  Parasites.     Sydenham  edition,  London,  1857,  pp.  115,  120. 


576  REPRODUCTION. 

find  their  way  out  singly  by  the  anus,  or  are  discharged  with  the 
evacuations.  They  have,  while  living,  considerable  power  of  con- 
tractility and  locomotion  ;  and  thus  become  transferred  to  neighboring 
table  substances,  which  arc  devoured  by  the  pig.  In  the  pig's 
stomach  and  intestine,  the  substance  of  the  articulation  is  digested  ; 
but  the  embryos,  which  are  but  little  over  30  mmm.  in  diameter,  and 
armed  with  movable  calcareous  spines,  make  their  way  through  the 
intestinal  walls,  and  are  thence  dispersed,  either  by  active  locomotion 
or  by  the  circulating  blood,  throughout  the  connective  tissue.  Here 
they  become  encysted,  and  go  through  with  a  partial  development,  until 
they  acquire  the  form  of  cysticercus.  In  this  condition  they  remain 
until  the  flesh  of  the  pig  is  used  for  food,  when  they  are  transformed, 
as  above  described,  into  taenia  solium,  thus  reproducing  the  original 
form  of  the  parasite.  A  similar  relation  has  been  found  by  Kiichen- 
meister  and  Siebold  between  certain  other  species  of  taenia  and  cysti- 
cercus. 

2.  Trichina  spiralis.  —  This  is  an  encysted,  worm-like  parasite,  found 
in  the  muscular  tissue  of  the  pig,  and  sometimes  in  that  of  the  rat,  the 

cat,  and   the   human  species.     Each 
FIG.  154.  worm  lies  spirally   coiled  within  its 

enveloping  cyst.  It  is  about  0.75 
millimetre  in  length,  with  a  tapering 
anterior  and  a  rounded  posterior  ex- 
tremity. It  has  a  nearly  straight 
intestine  and  rudimentary  sexual 


TRICHINA  SPIRALIS,  encysted,  from  muscii-    organs.     It  has  long-  been  recoffnized 

lar  tissue  of  a  trichinous  cat.    Magnified 

76  diameters.  as  an  occasional  parasite  in  the  mus- 

cular tissue  of  man  ;   but  it  is  only 

since  the  investigations  of  Leuckart*  and  Pagenstecher  f  that  the  his- 
tory of  its  growth  and  development  has  been  made  known.  If  muscu- 
lar flesh  containing  encysted  trichinae  be  administered  to  a  rabbit,  cat, 
rat,  mouse,  or  pig,  the  cysts  are  digested  and  the  worms  liberated  in 
the  intestine.  Here  they  rapidly  increase  in  development;  the  females 
becoming  impregnated  and  filled  with  living  young,  and  attaining,  at 
the  end  of  a  fortnight,  three  or  four  times  their  previous  size.  The 
embryos  are  now  discharged  into  the  cavity  of  the  intestine;  after 
which  they  penetrate  the  intestinal  walls,  and  thence  disperse  through- 
out the  body.  On  reaching  the  muscular  tissue,  they  become  encysted. 
and  thus  remain  quiescent  until  introduced  into  the  intestine  of  another 
animal  or  of  man.  The  existence  of  such  sexless  and  encysted  parasites 
is  therefore  analogous  to  that  of  the  caterpillar  or  the  maggot.  They 
are  sexless,  because  they  are  still  in  the  embryonic  condition.  ]>ut 
they  have  been  produced  by  generation  from  parents;  and  they  will, 
at  a  subsequent  period,  themselves  produce  young  bv  the  same  process. 

•   rntrrsiicliungen  fiber  Trichina  spiralis.     Leipzig  mid  IK-idulberg,  1860. 
f  Die  Trichinen.     Leipzig,  1800. 


THE    NATURE    OF    REPRODUCTION. 


577 


II.  Infusoria. — These  are  microscopic  organisms,  first  discovered  by 
Leeuwenhoek,  in  1675,  in  rain-water  which  had  been  kept  in  standing 
vases.  On  account  of  their  active  movement  and  minute  size  he  called 
them  "  animalcules ;"  but  as  they  were  soon  found  to  make  their 
appearance  in  great  numbers  and  with  remarkable  rapidity  in  watery 
infusions  of  organic  matter  exposed  to  the  air,  they  afterward  received 
the  general  name  of  "infusoria."  They  present  themselves  under  a 

FIG.  155. 


INFUSORIA,  of  various  kinds.— 1.  Urostyla  grandis,  from  decaying  sedge-grass.  2.  Paramecium 
aurelia,  from  vegetable  infusions.  3.  Chlamydodon  mnemosyne,  Baltic  Sea  water.  4.  Kerona 
polyporum,  on  the  fresh-water  polype.  5.  Oxytricha  caudata,  open  stagnant  waters.  6.  Ervilia 
fluviatilis,  clear  brook  water.  7.  Heteromita  ovata,  on  aquatic  river  plants.  Magnified  325 
diameters.  (Ehrenberg  and  Stein.) 

great  variety  of  forms;  so  much  so  that  Ehrenberg*  described  more 
than  700  different  kinds.  They  are  generally  provided  with  cilia 
attached  to  the  surface  of  their  bodies,  and  are,  for  the  most  part,  in 
constant  and  rapid  motion  in  the  fluid  which  they  inhabit. 

In  consequence  of  the  numerous  forms  of  the  infusoria,  their  fre- 
quent changeability  of  figure,  and  their  want  of  resemblance  to  any 
previously  known  organisms,  they  were  thought,  by  some  earlier 
observers,  to  have  no  regular  mode  of  generation,  but  to  arise  indis- 

*  Pie  Infusionsthierchen  als  vollkoramene  Organismen.     Leipzig,  1838. 

2M 


578  REPRODUCTION. 

criminately  from  the  organic  materials  of  the  infusion ;  the  particular 
form  which  they  might  assume  in  any  case  being  determined  by  the 
physical  conditions  present.  Their  inevitable  appearance  in  organic 
infusions,  under  ordinary  temperatures  and  exposures,  contributed 
to  this  belief.  The  substance  of  the  infusion  might  be  previously 
baked  or  boiled ;  the  water  in  which  it  was  infused  might  be  purified 
by  distillation  from  all  organic  contamination  ;  and  yet  infusoria  would 
make  their  appearance  at  the  usual  time  and  in  the  usual  abundance, 
provided  the  infusion  were  exposed  to  moderate  warmth  and  to  the 
access  of  air.  But  these  conditions  are  essential  to  all  organic  life,  and 
are  not,  therefore,  especially  requisite  for  infusoria. 

Consequently,  the  infusoria  must  either  have  been  spontaneously 
generated  from  the  materials  of  the  infusion,  or  else  their  germs  must 
have  been  introduced  from  without  In  the  latter  case  these  germs 
must  be  wafted  about  by  the  atmospheric  currents,  in  a  comparatively 
dry  and  inactive  condition,  to  resume  their  development  when  brought 
in  contact  with  moisture  and  the  requisite  organic  material. 

The  researches  relating  to  this  question  continued  from  1175,  when 
they  were  carried  on  by  Needham  and  Spallanzani,  throughout  the 
greater  part  of  the  present  century,  in  the  hands  of  Cuvier,  Schultze, 
Helmholtz,  Milne-Edwards,  Longet,  Pouchet,  Pasteur,  Wyman,  Tyn- 
dall,  and  Bastian.  The  main  object  of  investigation  was  to  discover, 
if  all  previous  living  germs  were  destroyed  by  heat,  and  the  access 
of  others  prevented  by  hermetically  sealing  the  vessels  or  thoroughly 
purifying  the  air  introduced,  whether,  under  such  circumstances,  infu- 
sorial life  would  be  developed. 

The  general  result  of  these  experiments  was  that  such  precautions 
diminished  and  often  prevented  the  production  of  infusoria.  Spallan- 
zani* had  already  shown,  in  1776,  that  organic  infusions  in  hermeti- 
cally sealed  flasks,  if  boiled  for  two  minutes,  failed  to  produce  any  of 
the  larger  and  more  highly  organized  animalcules ;  and  that  boiling  for 
three-quarters  of  an  hour  prevented  the  appearance  of  the  more  minute 
and  simpler  kinds. 

Schultze  f  performed  similar  experiments,  with  the  addition  of  admit- 
ting to  the  organic  infusion  purified  air.  He  placed  his  infusion  in  a 
glass  flask,  the  stopper  of  which  was  provided  with  two  narrow  tubes, 
bent  at  right  angles.  AVhcn  the  infusion  had  been  thoroughly  boiled, 
and  all  air  expelled  from  the  flask  by  the  vapor  of  ebullition,  he  fastened 
to  each  tube  a  series  of  bulbs  containing  on  one  side  sulphuric  acid,  ;m<l 
on  the  other  a  solution  of  potassium  hydrate;  so  that  the  air  which 
rei'-ntered  the  flask  while  cooling  must  pass  through  these1  fluids,  an<l 
thus  he  cleansed  of  all  livinir  organic  matter.  The  apparatus  was  then 
kept  in  a  warm  place  for  two  months,  during  which  time  the  air  was 
renewed  daily  by  suction  through  the  tubes,  without  any  infusoria  being 

Oj.uscdli  dc  Fisini  rinnnalr  r  Vf-ctahile.     Modena,  1770,  vol.  i.,  p.  10. 
f  Puggeiulorfs  Aimalrn,  l!\:}(}.     I5;md  xxxix.,  p.  487. 


THE  NATURE  OF  REPRODUCTION.         579 

detected  in  its  contents.  But  they  showed  themselves  in  abundance 
after  the  flask  had  been  opened,  and  the  infusion  exposed  for  a  few  days 
to  the  direct  access  of  air. 

Pasteur  *  found  that  if  a  flask  containing  an  organic  infusion  were 
boiled  upon  a  high  mountain,  where  the  air  is  of  unusual  purity,  allowed 
to  nil  itself  with  this  air  while  cooling,  and  then  hermetically  sealed,  it 
would  often  remain  free  from  infusorial  growth.  Several  such  flasks, 
boiled  and  filled  with  air  on  the  Montanvert  in  Switzerland,  were  kept 
for  four  years,  without  their  contents  undergoing  any  perceptible 
change.  But  on  making,  at  the  end  of  that  time,  a  minute  opening  in 
the  neck  of  one  flask,  the  infusion  exhibited  after  three  days  a  percepti- 
ble growth  of  cryptogamic  vegetation. 

These  results  did  not  absolutely  exclude  the  possibility  of  spontane- 
ous generation,  which  was  still  maintained  by  Pouchet  and  other  ob- 
servers ;  but  they  indicated  the  existence  of  atmospheric  germs,  capable 
of  development  in  a  suitable  organic  infusion. 

But  in  the  mean  time  the  study  oi"  the  infusoria  had  been  going  on 
independently  of  the  question  of  spontaneous  generation,  and  had  been 
sufficient  to  demonstrate  their  reproduction  in  the  usual  way,  by  fer- 
tilized eggs  and  embryonic  development. 

The  apparent  confusion  and  variability  in  form  of  the  infusoria,  at 
the  time  of  their  first  discovery,  depended  largely  on  their  great  num- 
bers and  imperfect  knowledge  of  their  natural  history.  Subsequent 
observation  has  shown  their  organization  to  be  as  definite  as  that  of 
other  classes  of  the  animal  kingdom  ;  and  they  have  now  been  arranged, 
by  the  labors  of  Claparede  and  Lachmann,f  Stein,  J  and  Balbiani,§  in 
orders,  families,  genera,  and  species,  which  may  be  recognized  with 
certainty  by  their  distinctive  marks.  They  are  not  confined  to  infusions 
of  decaying  material ;  but  many  have  their  natural  habitation  in  lakes, 
pools,  marshes,  running  brooks,  or  the  open  sea.  Certain  forms,  origi- 
nally included  in  this  class,  such  as  Rotifer,  Stephanoceros,  and  Flos- 
cularia,  have  been  found  to  possess  a  more  complicated  structure  than 
the  rest,  and  to  belong  properly  to  the  class  of  worms ;  their  mode  of 
reproduction  being  sufficiently  manifest  from  the  fact  that  they  often 
contain  living  embryos,  in  process  of  development. 

Finally,  the  true  ciliated  infusoria  have  also  been  shown  to  reproduce 
their  species  by  means  of  eggs,  formed  in  special  generative  organs  and 
fecundated  by  union  of  the  sexes  (Fig.  156).  This  fact,  first  demon- 
strated by  Balbiani,  has  been  since  confirmed,  in  numerous  instances, 
by  Stein,  Engelmann,||  and  Cohn  ;^f  Balbiani  and  Stein  together  having 

*  Comptes  Rendus  de  F  Academic  des  Sciences.     Paris,  Fevrier  20,  1865. 

f  Etudes  sur  les  Infusoires  et  les  Rhizopodes.     Geneve,  1856-1861. 

J  Organismus  der  Infusion sthiere.     Leipzig,  1859. 

2  Journal  de  la  Physiologic  de  1'Homme  et  des  Animaux.     Paris,  1861. 

||  Zeitschrift  fur  wissenschaftliclie  Zoologie.     Leipzig,  1862,  Band  xi.,  p.  347. 

fi  Ibid.    Band  xii.,  p.  197. 


580 


REPRODUCTION. 


observed  the  occurrence  of  sexual  generation  in  4T  different  genera  and 
66  different  species. 

Thus  the  infusoria  are  in  turn  excluded  from  the  field  of  spon- 
taneous generation.  But,  on  the  other  hand,  a  considerable  group  of 
organisms,  formerly  referred  to  this  class,  are  now  known  to  be  of  a 
different  character.  These  are  the  forms  included  under  the  general 

FIG.  156. 


STYLONYCHIA  MYTILUS  ;  a  fresh-water  infusorium.— 1.  Unimpregnated.  2.  Impregnated,  and  con- 
taining mature  eggs  and  two  embryos.  3.  Showing  the  form  of  the  embryo.  Magnified  375 
diameters.  (Stein.) 

term  of  Bacteria,  and  comprising  the  varieties  of  bacterium,  vibrio, 
spirillum,  and  micrococcus.  They  are  of  a  vegetable  nature,  notwith- 
standing  their  frequent  exhibition  of  active  movement ;  and  they  consist 
of  cells,  which  multiply,  often  with  great  rapidity,  by  repeated  subdi- 
vision. Whether  they  are  also  reproduced  by  germs,  has  not  been  deter- 
mined; but  their  minute  size  and  imperfect  classification  have  thus  far 
proved  obstacles  to  the  complete  study  of  their  physiological  character^. 
The  representative  of  this  irroup  is  the  species  known  as  Bacterium 
termo,  already  described  (page  78),  in  connection  with  the  phenomena 
of  putrefaction.  It  consists  of  rod-like  cells,  averaging  3  miuin.  in 
length  by  0.6  mmm.  in  thickness,  sometimes  single,  often  double,  two 


THE    NATURE    OF    REPRODUCTION. 


581 


FIG.  157. 


CELLS  OF  BACTERIUM  TERMO  ;  from  a  putrefying 
infusion. 


of  them  being  attached,  end  to  end.  The  latter  appearance  is  due  to 
their  multiplication  by  transverse  division,  which  takes  place  at  the 
middle  of  their  length.  The  two  new  cells  thus  produced  remain  for  a 
time  in  connection  with  each  other,  and  afterward  separate,  to  repeat 
the  process  independently.  Dur- 
ing a  considerable  part  of  their 
existence,  the  cells  are  in  rapid 
vibratory  and  progressive  move- 
ment. The  vibrations  take  place 
in  a  circular  manner,  about  a 
point  situated  at  or  near  one  of 
the  extremities ;  so  that  the  rest 
of  the  cell  performs  a  conical 
movement  around  this  point, 
presenting,  on  superficial  exami- 
nation, the  appearance  of  lateral 
oscillation.  The  mechanism  by 
which  this  movement  is  accom- 
plished is  unknown  ;  but  it  is  no 
doubt  analogous  to  the  slower 
spiral  undulations  of  the  Oscil- 
latorise,  among  fresh-water  algae; 
and  its  effect  is  to  propel  the 

bacterium  cells,  often  with  extreme  velocity,  through  the  fluid  in  which 
they  are  immersed. 

Of  late  years,  the  investigations  in  regard  to  spontaneous  generation 
have  been  mainly  confined  to  bacteria  and  their  allies,  since  they  now 
form  the  only  group  of  organisms  in  which  reproduction  by  generation 
has  not  been  established.  Even  for  them,  the  rapid  multiplication  by 
cell  division,  which  takes  place  under  favorable  conditions,  indicates 
their  usual  mode  of  increase ;  but  in  order  to  establish  an  entire  simi- 
larity between  them  and  other  living  organisms,  they  must  also  be 
shown  to  reproduce  by  spores  or  germs,  which  thus  far  has  not  been 
done.  The  experiments  with  boiled  infusions  in  sealed  flasks  have  led 
to  results  which  are  not  interpreted  in  the  same  manner  by  all  writers  ; 
but  it  is  evident  that  for  bacteria,  as  well  as  for  other  organic  forms, 
the  application  of  heat  exerts  in  various  degrees  a  preventive  action  on 
their  subsequent  appearance. 

The  experiments  of  Wyman*  on  this  subject  were  performed  with 
animal  and  vegetable  infusions,  which,  after  being  enclosed  in  sealed 
flasks,  with  atmospheric  air,  were  immersed  in  boiling  water  for  periods 
varying  from  thirty  minutes  to  five  hours,  and  afterward  kept  under 
observation  at  temperatures  favorable  for  the  development  of  bacteria. 
The  result  showed  that  the  appearance  of  these  organisms  was  always 
delayed  by  the  application  of  a  boiling  heat,  and  that  this  delay  was 


*  American  Journal  of  Science  and  Arts.  New  Haven,  vol.  xliv.,  September,  1867, 


582  REPRODUCTION. 

often  in  direct  proportion  to  the  length  of  the  boiling  process.  Further- 
more, in  certain  cases  the  bacteria  failed  to  be  produced  at  all,  and  the 
chance  of  their  production  was  found  to  decrease  in  proportion  to  the 
time  during  which  the  liquid  had  been  boiled.  Thus,  of  four  series  of 
flasks,  containing  the  same  infusion,  and  boiled  respectively  for  one,  two, 
three,  and  four  hours,  all  of  the  first  and  second  series  produced  bacteria, 
only  one  of  the  third,  and  none  of  the  fourth.  Finally,  in  no  instance, 
among  numerous  trials,  did  they  appear  in  any  infusion  which  had  been 
boiled  for  a  period  exceeding  five  hours.  Thus  a  limit  was  reached  to 
the  production  of  bacteria,  in  fluids  previously  subjected  to  the  action 
of  heat. 

There  can  be  no  doubt  as  to  the  bearing  of  these  and  similar  experi- 
ments. Spontaneous  generation  is  inadmissible  at  the  present  day  for 
everything  except  bacteria  ;  and  with  regard  to  them  there  is  no  suffi- 
cient proof  of  their  production  independently  of  previously  existing 
germs. 

Sexual  Generation. 

In  all  the  higher  plants  and  animals  generation  is  accomplished  by 
the  union  of  the  sexes.  Each  sex  is  distinguished  by  special  genera- 
tive organs,  male  or  female,  which  give  rise  to  a  peculiar  organized 
product ;  and  this  product  unites  with  that  from  the  opposite  sex,  to 
form  a  new  individual.  The  female  organs  produce  an  egg  or  germ 
capable  of  being  developed  into  the  young  animal  or  plant ;  the  male 
organs  produce  the  sperm  or  spermatic  fluid,  necessary  to  fecundate 
the  germ  and  communicate  to  it  the  stimulus  of  development. 

In  flowering  plants,  the  female  product  is  the  "germ ;"  which,  after 
fecundation  by  the  male  product  or  "  pollen,"  becomes  the  seed  or  fruit, 
and  may  produce  a  new  plant  by  further  development.  In  many  spe- 
cies, as  in  the'  lily,  the  violet,  the  convolvulus,  both  male  and  female 
organs  are  contained  in  the  same  flower ;  in  some  there  are  separate 
male  and  female  flowers  on  the  same  plant,  as  in  the  oak,  beech,  birch, 
and  hickory ;  and  in  others,  as  in  the  willow,  poplar,  and  sassafras,  the 
male  and  female  flowers  are  on  different  plants  of  the  same  species. 

In  animals  the  female  organs  produce  the  "ovum"  or  egg,  and  are 
called  ovaries.  The  male  organs,  which  give  rise  to  the  spermatic 
fluid,  are  the  testicles.  In  some  invertebrate  species,  as  in  the  snail, 
slug,  leech,  and  earthworm,  both  ovaries  and  testicles  are  present  in 
the  same  individual.  But  impregnation  is  nevertheless  effected  by  the 
sexual  union  of  two  organisms ;  the  eggs  produced  by  one  animal  being 
fecundated  by  the  seminal  fluid  of  another,  and  vice  versa. 

In  all  vertebrate  animals,  the  two  sets  of  generative  organs  are 
located  in  separate  individuals;  and  the  species  is  divided  into  two 
sexes,  male  and  female.  There  are  also,  for  the  i  iost  part,  accessory 
organs  of  ireneration,  which  assist,  in  the  accomplishment  of  the  pro- 
cess, and  occasion  a  Corresponding  difference  in  the  bodily  form.  In 
some  cases  this  dilVerence  is  so  great  that  the  male  and  female  would 
never  he  recognized  as  belonging  to  the  same  >pecies,  unless  Iliev  \\riv 


THE    NATURE    OF    REPRODUCTION.  583 

seen  in  company  with  each  other,  and  were  known  to  reproduce  by 
sexual  congress.  Not  to  mention  some  extreme  instances  of  this 
among  insects  and  other  invertebrate  animals,  it  is  sufficient  to  refer 
to  the  cock  and  the  hen,  the  lion  and  the  lioness,  the  buck  and  the  doe. 
In  man,  the  distinction  shows  itself  in  the  mental  constitution,  the  dis- 
position, habits,  and  pursuits  of  the  two  sexes,  as  well  as  in  the  general 
conformation  of  the  body,  and  its  external  appearance. 

The  special  details  of  the  generative  process  depend  on  the  struc- 
ture of  the  male  and  female  organs,  the  manner  in  which  the  sexual 
products  are  formed  and  discharged,  their  union  in  the  act  of  fecunda- 
tion, and  the  changes  which  take  place  in  the  development  of  the 
embryo. 


CHAPTER    II. 
THE  EGG,  AND  THE  FEMALE  ORGANS  OF  GENERATION. 

THE  egg,  in  man  and  mammalians,  is  a  globular  body,  about  0.25 
millimetre  in  diameter.  It  consists  of  an  external  closed  sac,  the 
vitelline  membrane,  containing  in  its  interior  a  spherical  mass,  the 
vitellus.  Of  these  two,  the  vitellus  is  the  essential  part  of  the  egg, 
since  from  its  substance  the  rudiments  of  the  embryo  are  formed.  The 
vitelline  membrane  is  a  protective  envelope,  serving  to  maintain  the 
form  and  integrity  of  the  vitellus. 

Vitelline  Membrane. — The  vitelline  membrane  is  a  smooth,  transpa- 
rent, colorless  layer,  about  0.01  millimetre  in  thickness.  With  a  mag- 
nifying power  sufficiently  moderate  to  in- 
elude  a  view  of  the  whole  egg,  it  presents  a 
perfectly  homogeneous  aspect ;  although  with 
higher  powers,  according  to  Klein,  it  exhibits 
an  appearance  of  vertical  striation.  Notwith- 
standing its  delicacy  and  transparency,  it  is 
very  elastic,  and  has  a  considerable  degree 
of  resistance.  If  the  mammalian  egg  be 
placed  under  the  microscope,  surrounded  by 
fluid  and  covered  with  a  thin  glass,  it  may 
HUMAN  OVUM,  magnified  75  ai-  be  perceptibly  flattened  by  pressure :  and 

ameters.  —  a.    Vitelliiie    mem-          ,   *  .  AH 

brane.  6.  vitellus.  c.  Germi-    when  the  pressure  is  removed  it  resumes  its 
native  vesicle,  d.  Germinative    globular  form.    When  slightly  compressed  in 
this  way,  the  apparent  thickness  of  its  vitel- 
line membrane  is  increased,  giving  it  the  appearance  of  a  rather  wide, 
pellucid  border  or  zone,  surrounding  the  granular  and  comparatively 
opaque  vitellus.    From  this  circumstance  it  has  received  the  name  of 
the  "zona  pellucida." 

In  the  vitelline  membrane  of  many  invertebrates,  and  also  in  that 
of  fishes,  a  minute  opening  has  been  discovered,  termed  the  "micro- 
pyle,"  leading  into  its  cavity ;  and  through  this  opening  the  spermatic 
filaments  of  the  male  reach  the  vitellus.  Such  an  opening  may  also  exist 
in  the  vitelline  membrane  of  other  vertebrate  animals  ;  but  the  globular 
form  of  the  egg,  the  homogeneous  texture  of  the  vitelline  membrane, 
and  the  absence  of  any  other  material,  of  different  refractive  power, 
in  the  orifice  of  the  micropyle,  are  obstacles  to  its  detection  under  the 
microscope. 

Vitellus. — The  vitellus  is  a  globular,  semifluid,  tenacious  mass  com- 
I toM'd  of  transparent  and  colorless  albuminous  material,  with  oleaginous- 
I« inking  granules  thickly  disseminated  throughout  its  substance.  Owing 

584 


THE  FEMALE  ORGANS  OF  GENERATION.     585 

to  the  admixture  of  these  two  constituents,  it  has  a  granular  aspect, 
and  a  considerable  degree  of  opacity.  Imbedded  in  the  vitellus,  near 
its  surface,  and  consequently  almost  immediately  beneath  the  vitelline 
membrane,  is  a  clear,  colorless,  transparent,  rounded  sac — the  germina- 
tive vesicle.  In  the  mammalian  egg,  this  vesicle  measures  about  .04 
millimetre  in  diameter.  It  presents  upon  its  surface  a  nucleus-like  spot, 
known  as  the  germinative  spot.  Both  the  germinative  vesicle  and  the 
germinative  spot  are  partially  concealed,  in  the  uninjured  condition  of 
the  egg,  by  the  granules  of  the  surrounding  vitellus. 

If  the  egg,  while  under  the  microscope,  be  ruptured  by  pressure  on 
the  cover-glass,  the  vitellus  is  gradually  expelled  by  the  elasticity  of 
the  vitelline  membrane.     It  retains  the  gran- 
ules imbedded  in  its  substance,  but  the  germi-  FIG.  159. 
native   vesicle   often    becomes    detached,   and 
therefore  more  distinctly  visible. 

In  man  and  mammalians,  the  simple  form  of 
egg  above  described  is  sufficient  for  the  pro- 
duction of  the  embryo,  since  it  is  retained,  after 
fecundation,  within  the  generative  passages, 
and  there  absorbs  the  nutritious  materials  for 
its  subsequent  growth.  In  the  naked  reptiles  ^UMA"N  OVUM,  ruptured  by 
and  in  most  fish,  where  the.  eggs  are  deposited  pressure,  showing  the  vitellus 
and  hatched  in  water,  the  vitellus  is  also  of  native  veside,  with  its  germi- 
small  size ;  since  the  hatching  takes  place  at  native  spot,  at  a,  and  the 

.     ,       „     ,         ,  smooth  fracture  of  the  vitel- 

an  early  period  of  development,  and  the  req-      Hne  membrane, 
uisite   additional  fluid   is   supplied   from   the 

surrounding  medium.  But  in  birds  and  most  of  the  scaly  reptiles, 
as  serpents,  turtles,  and  lizards,  the  eggs  are  deposited  in  a  nest  or  in 
the  ground,  with  no  external  source  of  nutrition  for  the  embryo.  In 
these  instances  the  vitellus,  or  "  yolk,"  is  of  large  size ;  and  the  bulk 
of  the  egg  is  further  increased  by  the  addition,  within  the  genera- 
tive passages,  of  albuminous  material  and  fibrous  or  calcareous  en- 
velopes. 

Ovaries  and  Oviducts. — The  eggs  are  produced  in  the  interior  of 
certain  organs,  situated  in  the  abdominal  cavity,  called  the  ovaries. 
These  organs  consist  of  a  mass  of  vascular  connective  tissue,  inclosing 
numerous  globular  sacs  or  follicles,  the  "  Graafian  follicles ;"  so  called 
from  the  anatomist  *  who  first  fully  described  them  as  constituent  parts 
of  the  ovary.  Each  Graafian  follicle  contains  an  egg,  which  varies 
more  or  less  in  size  and  appearance  in  different  classes  of  animals,  but 
which  has  always  the  same  essential  characters,  and  is  produced  in  the 
same  way. 

The  egg  thus  grows  in  the  ovarian  sac,  like  a  tooth  in  its  follicle ; 
and  forms,  accordingly,  a  constituent  part  of  the  body  of  the  female. 
It  is  subsequently  separated  from  its  attachments,  and  thrown  off;  but 

*  Regner  de  Graaf,  Opera  Omnia.     Amstelaedami,  1705,  p.  228. 


586 


REPRODUCTION. 


FIG.  160. 


until  that  time,  it  is  one  of  the  elements  of  the  ovarian  tissue,  and  is 
nourished  like  any  other  portion  of  the  female  organism. 

Since  the  ovaries  are  directly  concerned  in  the  production  of  the  egg, 
they  form  the  essential  part  of  the  female  generative  apparatus ;  but 
in  most  instances  there  are  also  accessory  organs,  which  take  part  in 
the  process  of  generation.  The  most  important  are  two  symmetrical 
tubes,  or  oviducts,  destined  to  receive  the  eggs  from  the  ovaries  and 
convey  them  to  the  external  generative  orifice.  The  mucous  mem- 
brane of  the  oviducts  is  usually  adapted  for 
supplying  certain  secretions  during  the  pas- 
sage of  the  egg,  which  complete  its  forma- 
tion or  provide  for  the  nutrition  of  the 
embryo. 

In  the  frog,  the  oviduct  commences  at  the 
upper  part  of  the  abdomen,  by  a  rather  wide 
orifice,  communicating  with  the  peritoneal 
cavity.  It  then  contracts  to  a  narrow  tube 
(Fig.  158),  folded  upon  itself  in  numerous 
convolutions,  until  it  opens,  near  its  fellow 
of  the  opposite  side,  into  the  "  cloaca  "  or 
lower  part  of  the  intestinal  canal.  This  is 
also  the  general  character  of  the  oviducts 
in  nearly  all  reptiles  and  birds. 

The  ovaries,  as  well  as  the  eggs  which 
they  contain,  undergo  at  certain  seasons  a 
periodical  development.  In  the  frog,  dur- 
ing the  latter  part  of  summer  and  in  autumn, 
the  ovaries  appear  like  clusters  of  nearly 
colorless  eggs,  the  smaller  of  which  are  per- 
fectly transparent  and  less  than  0.18  milli- 
metre in  diameter.  But  in  early  spring,  the  ovaries  enlarge  to  four  or 
five  times  their  former  size,  becoming  lobulated  masses,  crowded  with 
dark-colored  opaque  eggs,  each  two  millimetres  in  diameter.  At  the 
generative  season,  in  all  animals,  a  certain  number  of  eggs,  which 
were  previously  imperfect,  increase  in  size  and  become  altered  in  struct- 
ure. The  vitellus  especially,  at  first  colorless  and  transparent,  becomes 
larger  and  more  granular ;  assuming  a  black,  brown,  yellow,  or  orange 
hue.  In  the  mammalian  vitellus  the  change  consists  only  in  an  increase 
of  size  and  granulation,  without  remarkable  alteration  of  color. 

As  the  eggs  approach  maturity,  they  gradually  distend  the  Graafian 
follicles  and  project  from  the  surface  of  the  ovary.  When  fully  ripe, 
they  are  discharged  by  rupture  of  the  follicles,  and,  passing  into  the 
oviducts,  are  conveyed  to  the  external  generative  orifice,  and  there 
expelled.  In  successive  seasons,  successive  crops  of  egu-s  enlarge,  ripen, 
leave  the  ovaries,  and  are  discharged;  and  in  many  animals,  the  eggs 
of  no  less  than  three  different  crops  may  be  distinguished  in  the  ovary, 
namely  :  1st,  llmsr  which  are  mature  and  ready  to  be  discharged;  2d, 
those  which  are  to  ripen  in  the  following  season  ;  and  3d,  those  which 


FEMALE  GENERATIVE  ORGANS  OP 
FROG.— a.  a.  Ovaries.  6.  b.  Ovi- 
ducts, c.  c.  Their  upper  orifices. 
d.  Cloaca,  showing  lower  orifices 
of  oviducts. 


THE  FEMALE  ORGANS  OF  GENERATION.     587 

are  yet  inactive  and  undeveloped.  In  most  fish  and  reptiles,  as  well 
as  in  birds,  the  ripening  and  discharge  of  eggs  takes  place  once  a  year. 
In  different  quadrupeds  it  occurs  annually,  semi-annually,  bi-monthly, 
or  even  monthly ;  but  in  every  instance  it  is  periodical,  returning  at 
regular  intervals. 

Action  of  the  Oviducts  and  other  Generative  Passages. — In  the  frog, 
after  the  ripening  of  the  eggs  and  their  discharge  from  the  ovarian  fol- 
licles, they  receive  an  additional  investment  in  the  oviducts.  On  leav- 
ing the  ovary,  they  consist  only  of  the  dark-colored  granular  vitellus, 
inclosed  in  its  vitelline  membrane.  Their 
passage  through  the  oviduct  is  effected  by  FIG.  161. 

the   peristaltic   contraction   of  its   walls, 
aided  by  the  abdominal  muscles.     During 
this   passage,    an   albuminous   substance, 
secreted  by  the  oviduct,  is  deposited  round 
each  egg  in  successive  layers,  forming  a 
thick  envelope  (Fig.  161).    When  the  eggs 
are  discharged,  it  absorbs  moisture  from  . 
the  water  in  which  they  are  deposited,  and       through  the  oviduct, 
swells  into  a  transparent  gelatinous  mass, 

in  which  the  eggs  are  imbedded.  By  its  subsequent  liquefaction  and 
absorption,  it  supplies  material,  for  the  nourishment  of  the  embryo. 

In  scaly  reptiles  and  in  birds,  the  oviducts  perform  a  more  import- 
ant function.  In  the  common  fowl,  the  ovary  consists  of  follicles  of 
various  size,  loosely  united  by  connective  tissue,  and  containing  eggs 
in  different  stages  of  development  (Fig.  162,  a).  As  the  egg  which  is 
approaching  maturity  enlarges,  it  distends  its  follicle,  and  projects  from 
the  general  surface  of  the  ovary ;  so  that  it  bangs  at  last  into  the  peri- 
toneal cavity,  retained  only  by  the  attenuated  wall  of  the  follicle,  and 
a  slender  pedicle  containing  its  blood-vessels.  A  rupture  of  the  follicle 
then  occurs  at  its  most  prominent  part,  and  the  egg  is  discharged  from 
the  lacerated  opening. 

As  the  egg  leaves  the  ovary,  it  consists  of  a  large,  globular,  orange- 
colored  vitellus,  or  "yolk,"  inclosed  in  a  thin  and  transparent  vitelline 
membrane.  Immediately  beneath  the  vitelline  membrane,  on  the  sur- 
face of  the  vitellus,  is  a  round  white  spot,  consisting  of  a  layer  of 
minute  granules,  termed  the  "cicatricula,"  in  which  the  ge^minative 
vesicle  was  previously  imbedded.  At  this  time  the  germinative  vesicle 
has  usually  disappeared ;  but  the  cicatricula  is  still  an  important  part 
of  the  vitellus,  and  marks  the  spot  from  which  the  embryo  begins  its 
development. 

From  the  surface  of  the  ovary,  the  yolk  projects  into  the  orifice  of  the 
oviduct ;  and  when  discharged  from  its  follicle,  it  is  embraced  by  the 
expanded  upper  extremity  of  this  tube,  and  commences  its  downward 
passage.  In  the  fowl,  the  muscular  coat  of  the  oviduct  is  highly 
developed,  and  its  peristaltic  contractions  urge  the  egg  from  above 
downward,  somewhat  as  the  oesophagus  or  the  intestine  transports  the 


588 


REPRODUCTION. 


FIG.  162. 


food  in  a  similar  direction.  While  passing  through  the  first  five  OP 
six  centimetres  of  the  oviduct  (c,  d),  where  the  mucous  membrane  is 
smooth  and  transparent,  the  yolk  absorbs  a  certain  quantity  of  fluid, 
becoming  consequently  softer  and  more  flexible.  It  then  passes  into  a 
second  division  of  the  canal,  in  which  the  mucous  membrane  is  thicker 
and  more  glandular  in  texture,  and  arranged  in  longitudinal  folds. 

This  portion  (d,  e)  extends  over  about  22 
centimetres,  or  more  than  one-half  the 
length  of  the  oviduct.  In  its  upper  part, 
it  secretes  a  viscid  material,  which  con- 
solidates into  a  gelatinous  deposit  around 
the  yolk,  thus  forming  a  second  envelope, 
outside  the  vitelline  membrane. 

The  peristaltic  movements  of  the  ovi- 
duct are  such  as  to  give  a  rotary,  as  well 
as  a  progressive  motion  to  the  egg ;  and 
by  this  means  the  two  extremities  of  the 
gelatinous  envelope  become  twisted  in 
opposite  directions,  forming  rope-like  ex- 
tensions at  the  two  poles  of  the  egg.  They 
are  termed  the  "chalazse,"  or  suspensory 
cords,  and  the  membrane  with  which 
they  are  connected  is  the  "  chalaziferous 
membrane." 

Throughout  the  remainder  of  this  part 
of  the  oviduct,  an  albuminous  substance 
is  deposited  in  successive  layers  round 
the  yolk,  inclosing  the  chalaziferous  mem- 
brane and  chalazae.  This  substance,  the 
so-called  albumen,  or  "  white  of  egg,"  is 
gelatinous  in  consistency,  nearly  trans- 
parent, and  of  a  faint  amber  color.  It  is 
deposited  in  greater  abundance  in  front 
of  the  egg  than  behind  it,  and  thus  forms 
a  conical  projection  anteriorly,  while  be- 
hind, its  outline  is  parallel  with  the 
spherical  surface  of  the  yolk.  In  this  way, 
the  egg  acquires,  when  covered  with  its 
albumen,  an  ovoid  form,  of  which  one  end 
is  round,  the  other  pointed ;  the  pointed 
extremity  being  directed  downward,  as 
the  egg  descends  through  the  oviduct. 

FEMALE  GENERATIVK  OWJAXS  OK  THE  FOWL.— a.  Ovary.  6.  Graafian  follicle,  from  which  the 
egg  has  just  been  di -charged,  c.  Yolk,  entering  upper  extremity  of  oviduct.  <{,,•.  Second  por- 
tion nf  oviduct,  in  which  (lie  rhala/ifcTous  incmhraiir,  rhalu/:e,  and  albumen  are  formed,  f.  Third 
portion,  in  which  the  fibrous  shell  membranes  are  produced,  tj.  Fourth  portion  laid  open,  show- 
ing tin-  egg  completely  formed,  with  its  calcareous  shell,  h.  Canal  through  Avhich  the  egg  Is 
disch  . 


THE  FEMALE  ORGANS  OF  GENERATION.     589 

In  the  third  division  of  the  oviduct  (/),  which  is  about  nine  centi- 
metres in  length,  the  longitudinal  folds  of  the  mucous  membrane  are 
narrower  and  more  closely  packed  than  in  the  preceding  portion.  Its 
secretion  condenses  into  a  fibrous  covering,  composed  of  three  layers, 
closely  embracing  the  surface  of  the  albuminous  mass,  and  forming  a 
tough,  flexible,  semi-opaque  envelope  for  the  whole.  These  layers  are 
known  as  the  external,  middle,  and  internal  fibrous  membranes. 

Finally  the  egg  passes  into  the  fourth  division  of  the  oviduct  (g), 
which  is  wider  than  the  rest  of  the  canal,  but  only  a  little  over  five 
centimetres  in  length.  Its  mucous  membrane,  which  is  covered  with 
abundant  leaf-like  villosities,  exudes  a  fluid  rich  in  calcareous  salts. 
The  external  fibrous  layer  is  permeated  by  this  secretion ;  and  after- 
ward, owing  to  the  reabsorption  of  fluid,  the  calcareous  matter  is 
deposited  in  its  network.  The  deposit  goes  on,  growing  thicker  and 
more  condensed,  until  the  membrane  is  converted  into  a  white,  opaque, 
brittle,  calcareous  shell.  The  egg  is  then  forced  through  a  narrow  por- 

FIG.  163. 


DIAGRAM  OF  FOWL'S  EGG.— a.  Yolk,   f.  Vitelline  membrane,  c.  Chalazlferous  membrane,  d.  Albu- 
men,   e,  /.  Middle  and  internal  shell  membranes,    g.  Air-chamber,    ft.  Calcareous  shell. 

tion  of  the  oviduct  (h),  and,  gradually  dilating  the  passages  by  its  conical 
extremity,  is  discharged  from  the  external  orifice. 

The  egg  of  the  fowl,  after  expulsion,  consists,  accordingly,  of  the 
yolk  and  vitelline  membrane,  with  various  additional  parts  acquired 
during  its  passage  through  the  oviduct. 

After  the  discharge  of  the  egg  there  is  a  partial  evaporation  of  its 
watery  ingredients,  which  are  replaced  by  air  penetrating  through  the 
pores  of  the  shell  at  its  rounded  extremity.  The  air  thus  introduced 
accumulates  between  the  middle  and  internal  fibrous  membranes,  form- 
ing a  cavity  or  air-chamber  (Fig.  163,  g),  at  the  rounded  end  of  the  egg. 
Very  soon,  the  external  layers  of  the  albumen  liquefy ;  and  the  vitellus, 
being  specifically  lighter,  rises  toward  the  surface  of  the  egg,  with  the 
cicatricula  uppermost.  This  part  presents  itself  almost  immediately  on 
breaking  open  the  egg  at  any  point  corresponding  to  the  equator  of  the 


590  REPRODUCTION. 

yolk,  and  is  thus  placed  in  the  most  favorable  position  for  the  action  of 
warmth  and  air  in  the  development  of  the  chick. 

In  quadrupeds,  the  oviducts  present  a  further  modification.  The  egg, 
which  is  originally  of  minute  size,  is  retained  within  the  generative 
passages  during  the  development  of  the  embryo.  While  the  upper 
part  of  the  oviduct,  accordingly,  is  narrow,  and  serves  merely  to  trans- 
mit the  egg  from  the  ovary,  and  to  supply  it  with  a  little  albuminous 
secretion,  the  lower  portions  are  much  enlarged,  and  adapted  for  the 
protection  and  nourishment  of  the  embryo.  The  upper  and  narrower 
portions  of  the  oviduct  are  known  as  the  "  Fallopian  tubes,"  from  Fal- 
lopius*  who  first  described  them  in  the  human  female ;  while  the  lower 
and  larger  portions  constitute  the  uterus.  The  two  halves  of  the  uterus 
unite  with  each  other  on  the  median  line  near  their  inferior  termination, 
to  form  its  "body;"  while  the  ununited  parts  above  are  known  as  its 
"  cornua  "  or  horns. 

In  the  human  species,  the  ovaries  consist  of  Graafian  follicles,  imbed- 
ded in  a  somewhat  dense  connective  tissue,  supplied  with  blood-vessels, 

FIG.  164. 


UTERUS  AND  OVARIES  OF  THE  Sow.— a,  a.  Ovaries.    6,  6.  Fallopian  tubes,    c,  c.  Horns  of  the  uterus. 
d.  Body  of  the  uterus,     e.  Vagina. 

and  covered  with  an  opaque,  yellowish-white  layer  of  fibrous  tissue, 
called  the  "albugineous  tunic."  Its  peritoneal  layer  is  reflected  in  the 
usual  way  upon  the  blood-vessels  supplying  the  organ,  and  is  con- 
tinuous with  the  broad  ligaments  of  the  uterus ;  but  elsewhere  it  is 
closely  consolidated  with  the  albugineous  tunic. 

The  oviducts  commence  by  a  wide  expansion,  with  fringed  edges, 
called  the  "  fimbriated  extremity  of  the  Fallopian  tube."  For  most 
of  their  length  they  are  narrow  and  convoluted,  terminating,  on  each 
side,  in  the  body  of  the  uterus.  This  part  of  the  organ  is  so  much 
developed  at  the  expense  of  the  cornua,  that  the  latter  hardly  appear 
to  have  an  existence  in  the  human  species,  and  no  trace  of  them  is  visi- 
ble externally.  But  on  opening  the  uterus,  its  cavity  is  seen  to  be 
somewhat  triangular  in  shape,  its  upper  corners  running  out  to  join 
the  lower  extremities  of  the  Fallopian  tubes.  The  cornua  are  therefore 

*  Opera  Omnia.     Francofurti,  1600.     Observationes  Anatomicae,  p.  421. 


THE  FEMALE  ORGANS  OF  GENERATION 


591 


consolidated  with  the  body  of  the  uterus,  and  enveloped  in  its  thick 
layer  of  muscular  fibres. 

The  mucous  membrane  of  the  body  of  the  uterus  in  its  usual  condi- 
tion is  smooth,  of  a  rosy  color,  and  closely  adherent  to  the  subjacent 
muscular  tissue.  It  consists  of  tubular  follicles,  ranged  side  by  side, 
and  opening-  on  its  free  surface.  Their  secretion  is  probably  destined 
for  the  nutrition  of  the  embryo  during  the  early  periods  of  its  formation. 

The  cavity  of  the  body  of  the  uterus  terminates  below  by  a  con- 
stricted portion,  termed  the  os  internum,  by  which  it  is  separated  from 

FIG.  165. 


GENERATIVE  ORGANS  OF  THE  HUMAN  FEMALE— a,  a.  Ovaries.   6, 6.  Fallopian  tubes,  c.  Body  of  the 
uterus,    d.  Cervix,    e.  Vagina. 

the  cervix.  The  inner  surface  of  the  cervix  is  raised  in  prominent 
ridges,  arranged  usually  in  two  sets,  diverging  on  each  side  from  a 
central  longitudinal  ridge ;  presenting  the  appearance  known  as  the 
"arbor  vitae  uterina."  The  follicles  of  this  part  of  "the  uterine  mucous 
membrane  are  of  a  sac-like  form,  and  secrete  a  tenacious  mucus,  which 
serves  during  gestation,  to  block  up  the  cavity  of  the  cervix,  and  thus 
prevent  the  escape  or  injury  of  the  egg. 

The  cervix  uteri  presents  inferiorly  a  second  constriction,  the  "  os 
externum  ;"  and  below  this  comes  the  vagina,  constituting  the  last  divi- 
sion of  the  female  generative  passages. 

The  accessory  female  organs  of  generation  consist,  therefore,  of  ducts, 
through  which  the  egg  is  transported  from  within  outward,  varying  in 
development,  in  different  animals,  according  to  the  functions  which  they 
perform.  In  the  lower  orders,  they  serve  mainly  to  convey  the  egg 
to  the  exterior,  and  to  surround  it  more  or  less  abundantly  with  albu- 
minous secretions;  while  in  the  mammalia  and  in  man,  they  are  adapted 
to  the  more  important  office  of  retaining  the  egg  during  gestation  and 
providing  a  vascular  supply  for  the  nourishment  of  the  embryo. 


CHAPTER  III. 

THE  SPERMATIC  FLUID,  AND   THE  MALE  ORGANS  OF 
GENERATION. 

THE  mature  egg  is  not  by  itself  capable  of  being  developed  into  an 
embryo.  If  simply  discharged  from  the  ovary  and  carried  through 
the  oviducts  to  the  exterior,  it  dies  and  is  decomposed,  like  any  other 
part  of  the  body  separated  from  its  connections.  It  is  only  when  fecun- 
dated by  the  spermatic  fluid,  that  it  acquires  the  capacity  for  continued 
development. 

The  product  of  the  male  generative  organs  is  a  colorless,  somewhat 
viscid,  albuminous  fluid,  containing  minute  filamentous  bodies,  the  sper- 
matozoa. They  have  received  this  name  on  account  of  their  active  and 
continuous  movement,  suggesting  the  idea  of  independent  animal  organ- 
ization. 

Anatomical  Characters  of  the  Spermatozoa. — The  spermatozoa  of 
man  (Fig.  166,  a)  are  about  .045  millimetre  in  length,  according  to  the 
measurements  of  Kollikcr.  They  present  at  one  end  a  somewhat  flat- 
tened, triangular-shaped  enlargement,  termed  the  "head,"  which  consti- 
tutes about  one-tenth  part  of  their  length.  The  remaining  portion  is  a 
slender  filamentous  prolongation,  called  the  "tail,"  which  tapers  grad- 
ually backward,  becoming  toward  its  extremity  so  attenuated  that  it  is 
difficult  to  be  seen  except  when  in  motion.  There  is  no  further  organ- 
ization visible  in  the  spermatozoon ;  and  it  appears  to  consist,  so  far 
as  can  be  seen  by  the  microscope,  of  a  homogeneous  substance.  The 
terms  head  and  tail  are  not  used,  when  describing  the  spermatozoon, 
in  the  same  sense  as  that  in  which  they  would  be  applied  to  the  cor- 
responding parts  of  an  animal ;  but  simply  for  convenience,  as  one 
might  speak  of  the  head  of  an  arrow  or  the  tail  of  a  comet. 

In  vertebrate  animals,  generally,  the  spermatozoa  are  similar  in  form 
to  those  of  man ;  that  is,  they  are  filamentous  bodies,  with  the  ante- 
rior extremity  more  or  less  enlarged.  In  the  rabbit,  the  head  is 
roundish,  and  flattened,  somewhat  like  a  blood  globule.  In  the  rat  (Fig. 
166,  b)  it  is  conical,  often  slightly  curved  at  its  anterior  extremity  ;  and 
the  wholo  spermatozoon  is  much  longer  than  in  man,  measuring  nearly 
0.20  millimetre  in  length.  In  amphibia  and  reptiles  generally,  the 
spermatozoa  arc  longer  than  in  quadrupeds;  and  in  Menobranchus, 
they  are  (Fig.  166,  c),  not  less  than  0.57  millimetre  long,  about  one-third 
brin.ir  occupied  by  tin*  head  or  enlarged  portion  of  the  filament. 

The  most  remarkable  peculiarity  of  the  spermatozoa,  visible  by  the 
microscope,  is  their  movement.  In  a  drop  of  fresh  spermatic  fluid, 

592 


THE  MALE  ORGANS  OF  GENERATION. 


593 


FIG.  166. 


sufficiently  moistened  and  at  its  normal  temperature,  the  numberless 
filaments  with  which  it  is  crowded  are  seen  to  be  in  incessant  motion. 
In  many  species  of  animals,  the 
movement  of  the  spermatozoa 
strongly  resembles  that  of  a 
tadpole;  particularly  in  the 
mammalia,  where  they  consist 
of  a  short,  well-defined  head, 
with  a  long  and  slender  tail. 
The  tail-like  filament  is  in  con- 
stant lateral  vibration,  by 
which  the  spermatozoon  is 
driven  from  place  to  place  in 
the  surrounding  fluid,  as  a  fish 
or  a  tadpole  is  propelled 
through  the  water.  In  other 
instances,  as  in  the  Triton,  or 
water-lizard,  the  spermatozoa 
have  a  writhing  or  spiral-like 
movement ;  presenting  a  pecu- 
liarly striking  appearance  when 
large  numbers  are  viewed  to- 
gether. 

Notwithstanding  the  energy 
and  rapidity  of  this  movement, 
and  its  resemblance  in  mechan- 
ism to  animal  locomotion,  it  has 

no    analogy   with    a   Voluntary    SPERMATOZOA.— «..    Human.     6.  Of  the    rat.    c.  Of 


act. 


Menobranchus.    Magnified  480  times. 


The  spermatozoa  are  organic  forms,  produced  in  the  testicles,  and 
constituting  at  first  a  part  of  their  tissue.  Like  the  egg,  the  sperma- 
tozoon is  destined  to  be  discharged  from  the  organ  where  it  grew,  re- 
taining for  a  time  its  vital  properties.  One  of  these  properties  is  its 
power  of  movement ;  but  this  does  not  indicate  the  possession  of  in- 
dependent vitality,  and  is  not  even  a  proof  of  its  animal  origin.  The 
movement  of  a  spermatozoon  is  not  more  active  than  that  of  a  bac- 
terium cell,  or  of  the  ciliated  zoospores  of  certain  fresh-water  algae. 
It  is  analogous  to  the  motion  of  a  ciliated  epithelium  cell  detached 
from  its  mucous  membrane,  which  will  sometimes  continue  for  many 
hours,  under  favorable  conditions  of  temperature  and  moisture.  The 
movement  of  the  spermatozoa  continues  for  a  time  after  their  separa- 
tion from  the  body ;  but  it  is  limited  in  duration,  and  after  a  certain 
interval  comes  to  an  end. 

In  order  to  preserve  their  vitality,  the  spermatozoa  must  be  kept  at 
or  near  the  normal  temperature  of  the  body,  and  protected  from  the 
contact  of  air  or  other  unnatural  fluids.  If  the  spermatic  fluid  be 
allowed  to  dry,  or  if  it  be  diluted  with  water,  in  the  case  of  birds  and 

2N 


594  REPRODUCTION. 

quadrupeds,  or  if  subjected  to  extremes  of  heat  or  cold,  the  motion  of 
the  spermatozoa  ceases,  and  they  soon  disintegrate. 

Formation  of  the  Spermatozoa. — The  testicles,  within  which  the 
spermatozoa  are  produced,  are  the  characteristic  organs  of  the  male 
sex,  as  the  ovaries  are  characteristic  of  the  female.  In  man  and  mam- 
malia, they  are  solid,  ovoid-shaped  bodies,  composed  mainly  of  long, 
narrow,  convoluted  tubes,  the  "  seminiferous  tubes,"  lying  for  the  most 
part  closely  in  contact  with  each  other,  and  separated  only  by  capillary 
blood-vessels  and  a  little  connective  tissue.  The  seminiferous  tubes 
commence,  by  rounded  extremities,  near  the  external  surface  of  the 
testicle  and  pursue  an  intricately  convoluted  course  toward  its  central 
;u id  posterior  part.  They  are  not  strongly  adherent  to  each  other,  and 
may  be  readily  unravelled  by  manipulation. 

According  to  Kolliker,  the  formation  of  the  spermatozoa  takes  place 
within  peculiar  cells  occupying  the  cavity  of  the  seminiferous  tubes. 
As  puberty  approaches,  beside  the  ordinary  pavement  epithelium  lining 
the  tubes,  larger  cells  make  their  appearance,  each  containing  from  one 
to  twenty  nuclei,  with  nucleoli.  In  these  cells  the  spermatozoa  are 
formed;  their  number  corresponding  usually  with  that  of  the  cell- 
nuclei.  They  are  developed  in  bundles,  held  together  by  the  mem- 
branous envelope  surrounding  them,  but  are  afterward  set  free  by 
the  liquefaction  of  the  cell-wall,  and  mingled  with  a  small  quantity  of 
transparent  fluid. 

While  in  the  seminiferous  tubes,  the  spermatozoa  remain  inclosed  in 
their  parent  vesicles ;  they  are  liberated,  and  mingled  together,  only 
after  entering  the  rete  testis  and  the  head  of  the  epididymis. 

Accessory  Male  Organs  of  Generation. — Beside  the  testicles,  there 
are  certain  accessory  organs  by  which  the  spermatic  fluid  is  conveyed 
to  the  exterior,  and  mingled  with  various  secretions  which  assist  in  the 
accomplishment  of  its  function. 

As  the  spermatozoa  leave  the  testi'cle,  they  are  crowded  together  in 
an  opaque,  white,  semi-fluid  mass,  which  fills  the  vasa  efferentia,  and 
distends  their  cavities.  It  then  enters  the  single  duct  forming  the  body 
and  lower  extremity  of  the  epididymis,  following  the  tortuous  course 
of  this  tube,  until  it  reaches  the  vas  deferens,  by  which  it  is  conveyed 
to  the  vesiculae  seminales.  Throughout  this  course  it  is  mingled  with 
a  scanty  mucus-like  fluid,  secreted  by  the  epididymis  and  vas  deferens. 
The  vesiculse  seminales  also  contain  a  fluid  secretion,  which  serves 
some  secondary  purpose  in  completing  the  formation  of  the  sperm. 
One  of  its  functions  is  no  doubt  to  dilute  the  mass  of  spermatozoa, 
and  give  them  liberty  of  motion ;  as  well  as  to  increase  the  volume 
of  the  spermatic  fluid,  and  thus  enable  it  to  be  expelled  by  the  mus- 
cular contraction  of  the  parts  about  the  urethra.  Kolliker  has  found 
the  spermatozoa  in  the  vas  deferens  and  epididymis  generally  quiescent : 
their  motion  being  exhibited  only  in  the  vesicula3  seminales  and  in  the 
ejaculated  sperm. 

At  the  moment  of  its  evacuation,  the  sperm  first  passes  from  the 


THE  MALE  ORGANS  OF  GENERATION.       595 

vesiculae  seminales  into  the  prostatic  portion  of  the  urethra,  where  it 
meets  with  the  secretion  of  the  prostate  gland,  then  poured  out  in 
unusual  abundance ;  and  farther  on,  there  are  added  the  secretions  of 
Cowper's  glands  and  of  the  remaining  mucous  follicles  of  the  urethra. 
All  these  increase  the  volume  of  the  spermatic  fluid,  and  serve  as 
vehicles  for  the  transport  of  the  spermatozoa. 

Conditions  of  Fecundation  by  the  Spermatic  Fluid. —  There  are 
several  conditions  which  are  essential  to  the  accomplishment  of  fecun- 
dation. 

First,  the  spermatozoa  must  be  present  and  in  a  state  of  vitality. 
Of  all  the  organic  ingredients,  derived  from  different  sources,  which 
go  to  make  up  the  spermatic  fluid,  the  spermatozoa  form  the  essential 
part.  They  are  the  fecundating  element  of  the  sperm,  while  the  rest 
perform  only  accessory  functions. 

Spallanzani*  found  that  if  frog's  sperm  be  passed  through  a  succes- 
sion of  filters,  so  as  to  separate  the  solid  from  the  liquid  portions,  the 
filtered  fluid  is  destitute  of  fecundating  properties ;  while  the  sperma- 
tozoa entangled  in  the  filter,  if  mixed  with  a  sufficient  quantity  of 
fluid,  may  be  successfully  used  for  the  impregnation  of  eggs.  The 
removal  of  both  testicles  destroys  the  power  of  impregnating  the 
female,  notwithstanding  that  all  the  other  generative  organs  may 
remain  uninjured.  The  spermatic  fluid,  furthermore,  must  be  in  a 
fresh  condition,  and  the  spermatozoa  must  retain  their  anatomical 
characters  and  their  active  movement.  The  experiments  of  Spallan- 
zani have  shown  that,  if  the  above  conditions  be  preserved,  the  fluid, 
removed  from  the  spermatic  ducts  of  the  male,  is  capable  of  fecun- 
dating the  eggs  of  the  female.  But  if  exposed  for  a  certain  time  to 
the  atmosphere,  or  to  unnatural  temperatures,  it  becomes  inert.  So 
long  as  the  spermatozoa  continue  in  active  motion,  they  are  usually 
found  to  retain  their  physiological  properties  ;  the  cessation  of  move- 
ment indicating  that  their  vitality  is  exhausted,  and  that  they  are  no 
longer  capable  of  impregnating  the  egg. 

Secondly,  both  eggs  and  spermatozoa  must  have  arrived  at  a  certain 
degree  of  development  before  fecundation  can  take  place.  Previous  to 
this  time  the  immature  eggs  are  incapable  of  being  impregnated,  and 
the  imperfectly  developed  spermatozoa  have  not  yet  acquired  their 
fecundating  power.  The  necessary  growth  takes  place  within  the 
generative  organs ;  and  when  it  is  complete,  both  spermatozoa  and 
eggs  are  ready  to  be  discharged,  and  are  in  condition  to  exert  and 
receive  the  necessary  influence. 

The  fecundating  power  of  the  spermatozoa  is  exceedingly  active. 
Spallanzani  found  one-fifth  of  a  gramme  of  the  spermatic  fluid  of  the 
frog,  diffused  in  water,  sufficient  for  the  impregnation  of  several  thou- 
sand eggs.  The  process  seems  to  be  accomplished  almost  instanta- 
neously, "  since  eggs  which  were  allowed  to  remain  in  the  fecundating 

*  Experiences  pour  servir  a  1'Histoire  de  la  Generation.     Geneve,  1786. 


596  REPRODUCTION. 

mixture  for  only  one  second  proved  to  be  impregnated,  and  were  after- 
ward hatched  at  the  usual  period." 

Thirdly,  the  spermatozoa  must  come  in  direct  contact  with  the  egg 
or  its  envelopes.  Spallanzani  first  demonstrated  this  by  attaching  ma- 
ture eggs  to  the  concave  surface  of  a  watch-glass,  which  he  placed,  in- 
verted, over  a  second  watch-glass  containing  spermatic  fluid.  The  eggs, 
exposed  in  this  way  for  several  hours  to  the  vapor  of  the  fluid  without 
touching  its  surface,  were  afterward  found  to  have  failed  of  impregna- 
tion ;  while  others,  which  had  been  moistened  with  the  same  spermatic 
fluid,  became  developed  into  tadpoles. 

Finally,  in  the  act  of  fecundation  the  spermatozoa  penetrate,  through 
the  vitelline  membrane,  to  the  vitellus.  This  fact,  first  observed  by 
Barry*  in  the  rabbit,  has  subsequently  been  seen  by  Newport  f  in  the 
frog,  by  Bischoff,  by  Coste,  by  Kobin  J  in  a  species  of  leech,  by  Flint  § 
in  the  pond  snail,  and  by  Weil,||  in  repeated  instances,  in  the  rabbit. 
According  to  some  of  these  observations,  the  penetration  of  the  sper- 
matozoon takes  place  by  a  small  orifice  or  "micropyle"  in  the  vitelline 
membrane,  as  first  indicated  by  Barry.  In  others  no  such  orifice  has 
been  visible ;  the  spermatozoa  appearing  to  perforate  the  vitelline  mem- 
brane by  the  impulsive  movement  of  their  filamentous  extremity  (New- 
port). Such  a  mode  of  penetration  is  not  inadmissible,  since  it  is  known 
that  the  much  larger  embryos  of  taenia  and  trichina  make  their  way 
without  difficulty  through  the  substance  of  the  intestinal  mucous  mem- 
brane. 

After  their  arrival  in  the  vitelline  cavity,  the  spermatozoa  disappear 
as  distinct  organic  elements.  Their  substance  unites  with  that  of  the 
vitellus ;  and  thenceforward  the  fecundated  egg  is  derived  from  both 
male  and  female  organisms.  The  greater  portion  of  its  material  is  pro- 
duced by  the  female ;  but  that  which  is  supplied  from  the  seminal  fila- 
ments of  the  male  is  equally  essential  for  the  production  of  an  embryo. 
The  offspring,  accordingly,  may  exhibit  resemblances  to  either  or  both 
of  the  parents,  since  it  originates  from  both  the  generative  products. 

Union  of  the  Sexes. — In  most  animals  there  is  a  periodical  develop- 
ment of  the  testicles  in  the  male,  corresponding  in  time  with  that  of  the 
ovaries  in  the  female.  As  the  ovaries  enlarge  and  the  eggs  ripen  in 
one  sex,  the  testicles  of  the  other  increase  in  size,  and  become  turgid 
with  spermatozoa.  The  accessory  organs  of  generation  at  the  same 
time  exhibit  an  unusual  activity  of  nutrition,  increasing  in  vascularity 
and  preparing  to  perform  their  part  in  reproduction. 

In  fishes,  as  a  rule,  the  testicles  occupy,  in  the  abdomen  of  the  male, 
the  same  relative  position  as  the  ovaries  in  the  female ;  and,  as  they 

*  Philosophical  Transactions.     London,  1840,  p.  533,  and  1843,  p.  33. 
f  Ibid.,  1853,  p.  271. 

J  Journal  de  la  Physiologic  de  THomrae  et  des  Animaux.  Paris,  1862,  tome  v., 
p.  80. 

g  Physiology  of  Man.     New  York.  1874,  vol.  v.,  p.  352. 
U  Strieker's  Medicini.scher  Juhrbucher.     Wien,  1873,  p.  18. 


THE    MALE    ORGANS    OF    GENERATION.  597 

become  distended  with  their  contents,  they  project  into  the  peritoneal 
cavity.  Each  of  the  sexes  is  then  under  the  influence  of  a  correspond- 
ing excitement.  The  unusual  development  of  the  reproductive  organs 
reacts  upon  the  general  system,  producing  a  peculiar  condition,  known 
as  "  erethism."  The  female,  distended  with  eggs,  feels  the  stimulus 
which  leads  to  their  expulsion  ;  while  the  male,  bearing  the  weight  of 
the  enlarged  testicles  and  the  accumulation  of  newly-developed  sper- 
matozoa, is  impelled  by  a  similar  sensation  to  the  discharge  of  the 
spermatic  fluid.  The  two  sexes  are  led  by  instinct  at  this  season  to 
frequent  the  same  situations.  The  female  deposits  her  eggs  in  some 
spot  favorable  to  their  protection  and  development;  after  which  the 
male,  apparently  attracted  and  stimulated  by  the  sight  of  the  new-laid 
eggs,  discharges  upon  them  the  spermatic  fluid,  and  thus  effects  their 
impregnation.  It  is  in  this  way  that  fecundation  takes  place  in  nearly 
all  the  osseous  fishes. 

In  instances  like  the  above,  where  the  male  and  female  generative 
products  are  discharged  separately,  their  subsequent  contact  would 
seem  to  be  dependent  on  fortuitous  circumstances,  and  impregnation, 
therefore,  liable  to  fail.  But,  in  fact,  the  simultaneous  excitement 
of  the  sexes,  leading  them  to  ascend  the  same  rivers  and  to  frequent 
the  same  localities,  provides  with  sufficient  certainty  for  impregnation. 
The  number  of  eggs  produced  by  the  female  is  also  very  large,  the 
ovaries  being  often  so  distended  as  nearly  to  fill  the  abdominal  cav- 
ity ;  so  that,  although  many  eggs  may  be  accidentally  lost,  a  sufficient 
number  are  still  impregnated  to  provide  for  the  continuation  of  the 
species. 

In  cartilaginous  fishes,  as  in  sharks,  rays,  and  skates,  an  actual  con- 
tact takes  place  between  the  sexes,  and  the  spermatic  fluid  of  the  male 
is  introduced  into  the  female  generative  passages.  Thus  the  eggs  are 
fecundated  within  the  body  of  the  female,  and  in  many  species  go 
through  with  a  nearly  complete  development  in  this  situation  and  the 
young  arc  born  alive. 

In  the  frog,  the  male  fastens  himself  on  the  back  of  the  female  by 
means  of  the  anterior  limbs,  which  retain  their  hold  by  spasmodic  con- 
traction. This  continues  for  one  or  more  days,  during  which  time  the 
mature  eggs,  after  being  discharged  from  the  ovary,  are  passing  through 
the  oviducts.  As  they  are  expelled  from  the  anus,  the  spermatic  fluid 
is  discharged  upon  them,  and  impregnation  takes  place. 

In  serpents,  lizards,  and  turtles,  the  sperm  is  introduced  into  the 
female  generative  passage  at  the  time  of  copulation,  by  means  of  an 
erectile  male  organ.  Of  these  animals,  some  lay  their  eggs  immedi- 
ately after  fecundation,  others  retain  them  until  the  embryo  is  partly 
developed. 

In  birds,  the  spermatozoa  are  introduced  into  the  sexual  orifice  of  the 
female,  and  make  their  way  into  the  upper  portion  of  the  oviduct,  where 
they  may  be  found  in  active  motion,  mingled  with  the  secreted  fluids 


598  REPRODUCTION. 

of  this  part  of  the  canal.*  The  vitellus  is  thus  fecundated  immediately 
upon  its  discharge  from  the  ovary,  and  before  it  has  become  surrounded 
with  the  albuminous  envelopes  supplied  by  the  oviduct. 

Lastly,  in  man  and  mammalians,  where  the  impregnated  egg  is 
retained  within  the  body  of  the  female  during  the  whole  of  its  devel- 
opment, the  spermatic  fluid  is  introduced  into  the  vagina  and  uterus 
by  sexual  congress,  and  meets  the  egg  at  or  soon  after  its  discharge 
from  the  ovary.  A  close  correspondence  between  the  periods  of  sexual 
excitement,  in  the  male  and  the  female,  is  visible  in  many  of  these  ani- 
mals, as  well  as  in  fish,  birds,  and  reptiles.  This  is  the  case  in  most 
species  which  produce  young  but  once  a  year,  as  the  deer,  the  wolf, 
and  the  fox.  In  others,  such  as  the  dog,  the  rabbit,  and  the  guinea-pig, 
where  several  broods  of  young  are  produced  annually,  or  where,  as  in 
man,  the  generative  epochs  of  the  female  recur  at  short  intervals,  the 
time  of  impregnation  is  comparatively  indefinite,  and  the  generative 
apparatus  of  the  male  is  almost  constantly  in  full  development.  It  is 
excited  to  action  at  particular  periods,  apparently  by  some  influence 
derived  from  the  condition  of  the  female. 

In  quadrupeds  and  in  man,  the  contact  of  the  sperm  with  the  egg, 
and  the  fecundation  of  the  latter,  take  place  in  the  generative  passages 
of  the  female ;  either  in  the  uterus,  the  Fallopian  tubes,  or  on  the  sur- 
face of  the  ovary — in  each  of  which  situations  the  spermatozoa  have 
been  found  after  sexual  intercourse. 

*  Foster  and  Balfour,  Elements  of  Embryology.     London,  1874,  p.  21. 


CHAPTER  IV. 
OVULATION  AND   MENSTRUATION. 

Ovnlation. 

THE  periodical  ripening  of  the  eggs  and  their  discharge  from  the 
ovaries  constitute  the  process  of  "  ovulation,"  which  may  be  con- 
sidered as  the  primary  act  of  reproduction.  Its  characteristic  phenom- 
ena depend  on  the  following  general  laws,  which  apply  with  but  little 
variation  to  all  classes  of  animals. 

1.  Eggs  exist  originally  in  the  ovaries,  as  part  of  their  structure. 
In  fish,  reptiles,  and  birds,  the  ovary  is  comparatively  simple,  consist- 
ing only  of  Graafian  follicles,  united  by  connective  tissue,  and  thus 
aggregated  into  the  form  of  a  rounded,  elongated,  or  lobulated  organ. 
In  the  mammalians  and  in  man,  its  essential  constitution  is  the  same ; 
but  its  connective  tissue  is  denser  and  more  abundant,  and  its  texture 
more  compact.  In  all  classes  each  Graafian  follicle  contains  an  egg, 
which  varies  in  size  in  different  species  and  at  different  periods  of 
growth. 

The  process  of  reproduction  is  not  essentially  different  in  oviparous 
and  viviparous  animals.  In  the  oviparous  classes,  including  most  fishes 
and  reptiles  and  all  birds,  the  female  produces  an  egg,  of  considerable 
size,  from  which  the  young  is  afterward  hatched ;  while  in  those  which 
are  viviparous  the  young  is  brought  forth,  already  formed  and  alive, 
from  the  body  of  the  female.  But  examination  shows  that  the  ovaries 
of  viviparous  animals  also  contain  eggs,  analogous  to  those  of  the 
ovipara,  though  of  smaller  size  and  comparatively  simple  structure. 

The  distinction  between  the  two  classes,  so  far  as  regards  the  process 
of  reproduction,  is  therefore  apparent  rather  than  fundamental.  In  the 
oviparous  fish,  reptiles,  and  birds,  the  egg  is  discharged  before  or  im- 
mediately after  impregnation,  the  embryo  being  developed  and  hatched 
externally.  In  quadrupeds  and  in  man,  on  the  other  hand,  the  egg  is 
retained  within  the  body  of  the  female  until  the  formation  of  the 
embryo  is  complete ;  when  the  membranes  are  ruptured  and  the  young 
expelled.  But  in  all  instances,  the  young  is  produced  from  an  egg ; 
and  the  egg,  though  presenting  variations  of  size  and  structure,  always 
consists  essentially  of  a  vitellus  and  a  vitelline  membrane,  and  is  first 
formed  in  the  interior  of  an  ovarian  follicle. 

The  egg  is  accordingly  a  part  of  the  ovarian  tissue.  It  exists  before 
the  generative  function  is  established,  and  during  the  earliest  periods 
of  life.  It  is  found  without  difficulty  in  the  newly-born  female  infant, 
and  may  even  be  detected  in  the  ftetus  before  birth.  Its  nutrition  is 

599 


600  REPRODUCTION. 

provided  for  in  the  same  manner  with  that  of  other  parts  of  the  bodily 
structure. 

2.  The  ovarian  eggs  become  more  fully  developed  at  a  certain  age 
when  the  generative  function  is  about  to  be  established.     During  the 
early  periods  of  life,  the  ovaries  and  their  contents,  like  many  other 
organs,  are  imperfectly  developed.    They  exist,  but  they  are  as  yet  inca- 
pable of  functional  activity.     In  the  young  chick,  the  ovary  is  small ; 
and  the  eggs,  instead  of  presenting  a  voluminous,  yellow,  opaque  vitel- 
lus,  are  minute,  transparent,  and  colorless.     In  young  quadrupeds,  and 
in  the  human  female  during  infancy  and  childhood,  the  ovaries  are 
equally  quiescent.     They  are  small,  friable,  and  of  nearly  homogeneous 
appearance  to  the  naked  eye ;  presenting  none  of  the  enlarged  follicles, 
filled  with  transparent  fluid,  which  afterward  become  a  characteristic 
feature  of  their  structure.      At  this  time,  accordingly,  the  ovaries  are 
inactive,  the  eggs  which  they  contain  immature,  and  the  female  inca- 
pable of  bearing  young. 

But  at  a  certain  period,  which  varies  in  the  time  of  its  occurrence 
in  different  species,  the  sexual  apparatus  enters  upon  a  state  of  activity. 
The  ovaries  increase  in  size,  and  their  eggs,  which  have  previously 
remained  quiescent,  take  on  a  rapid  growth,  the  structure  of  the  vitellus 
being  completed  by  a  deposit  of  semi-opaque  granular  matter  in  its 
substance.  In  this  condition,  the  eggs  are  ready  for  impregnation,  and 
the  female  becomes  capable  of  bearing  young.  She  is  then  said  to  have 
arrived  at  the  state  of  "  puberty,"  in  which  the  generative  organs  are 
fully  developed.  This  change  is  accompanied  by  a  corresponding  altera- 
tion in  the  system  at  large.  In  many  birds,  the  plumage  assumes 
more  varied  and  brilliant  colors ;  and  in  the  common  fowl,  the  comb, 
or  "crest,"  enlarges  and  becomes  red  and  vascular.  In  the  American 
deer  (Cervus  virginianus),  the  coat,  which  during  the  first  year  is  mot- 
tled with  white,  changes  in  the  second  year  to  a  reddish  tinge.  In 
nearly  all  species,  the  limbs  become  more  compact  and  the  body  more 
rounded ;  and  the  whole  external  appearance  is  so  altered  as  to  indicate 
that  the  animal  has  arrived  at  the  period  of  puberty,  and  is  capable 
of  reproduction. 

3.  In  the  adult  female,  successive  crops  of  eggs  ripen  and  are  dis- 
charged by  rupture  of  the  Graafian  follicles.      The  eggs  are  not  only 
formed  and  attain  their  growth  within  the  ovaries,  but  they  are  also 
ripened  and  disrlmr.irrd,   irrespective  of  sexual  intercourse,  from  the 
independent    functional  activity  of  the  female  organism.      In   many 
fishes  and  reptiles,  the  mature  eggs  h>:m>  the  ovary,  pass  through  the 
oviducts,  and  arc  discharged  before  coming  in  contact  with  the  sperm- 
atic fluid  of  the  malr.     The  domestic  fowl,  if  well  supplied  with  nour- 
ishment, will  continue  to  lay  eggs  without  the  presence  of  the  cock ; 
only  these  eggs,  not  having  been  fecundated,  cannot  produce  chicks. 
In  oviparous  animals,  therefore,  the  discharge  of  the  egg,  as  well  as 
its  formation,  may  take  place  independently  of  sexual  intercourse. 

This  is  also  true  of  the  vivipara.     The  observations  of  Bischoff, 


OVULATION    AND    MENSTRUATION.  601 

Pouchet,  and  Coste,  on  the  sheep,  the  pig,  the  bitch,  and  the  rabbit, 
have  demonstrated  that  if  the  female  be  kept  from  the  male  until  after 
puberty,  and  then  killed,  examination  of  the  ovaries  will  sometimes 
show  that  Graafian  follicles  have  matured,  ruptured,  and  discharged 
their  eggs,  though  no  sexual  intercourse  has  taken  place.  Sometimes 
the  follicles  are  found  distended  and  prominent  on  the  surface  of  the 
ovary ;  sometimes  recently  ruptured  and  collapsed  ;  or  in  various  stages 
of  cicatrization  and  atrophy.  Bischoff,*  in  several  instances  of  this 
kind,  found  the  unimpregnated  eggs  in  the  oviduct,  on  their  way  toward 
the  uterus.  In  species  where  the  ripening  of  the  eggs  takes  place  at 
short  intervals,  as  in  the  sheep,  the  pig,  or  the  cow,  it  is  very  rare  to 
examine  the  ovaries  without  finding  traces  of  a  more  or  less  recent 
rupture  of  Graafian  follicles. 

One  of  the  most  important  facts,  derived  from  these  observations,  is 
that  the  ovarian  eggs  become  developed  and  are  discharged  in  succes- 
sive crops,  and  at  regular  intervals.  In  the  ovary  of  the  fowl  (Fig.  162), 
it  may  be  seen  at  a  glance  that  the  eggs  grow  and  ripen,  one  after  the 
other,  like  fruit  upon  a  vine.  In  this  instance,  the  process  of  evolution 
is  rapid ;  and  it  is  easy  to  distinguish,  at  the  same  time,  eggs  which 
are  almost  microscopic  in  size,  colorless,  and  transparent ;  those  which 
are  larger,  somewhat  opaline,  and  yellowish ;  and  finally  those  which 
are  fully  developed,  of  a  deep,  opaque  orange  hue,  and  nearly  ready  to 
leave  the  ovary. 

The  difference  between  the  undeveloped  and  mature  eggs,  in  the  fowl's 
ovary,  consists  mainly  in  the  size  of  the  vitellus ;  and  the  ovarian  fol- 
licle is  distended  and  ruptured,  and  the  egg  finally  set  free,  owing  to 
the  pressure  of  the  enlarged  vitellus. 

In  man  and  mammalians,  on  the  other  hand,  the  microscopic  egg 
never  becomes  large  enough  to  distend  the  Graafian  follicle  by  its  own 
size.  The  rupture  of  the  follicle  and  the  liberation  of  the  egg  are  pro- 
vided for,  in  these  instances,  by  the  following  mechanism. 

In  the  earlier  periods  of  life,  in  man  and  mammalians,  the  egg  is 
contained  in  a  Graafian  follicle  which  closely  embraces  its  exterior,  being 
hardly  larger  than  the  egg  itself.  As  puberty  approaches,  the  follicles 
situated  near  the  surface  of  the  ovary  become  enlarged  by  the  accumu- 
lation of  serous  fluid  in  their  cavity.  At  that  time,  the  ovary  contains 
a  number  of  transparent  vesicles,  the  smallest  of  which  are  deep  seated, 
and  which  increase  in  size  as  they  approach  the  free  surface  of  the 
organ.  These  are  the  Graafian  follicles,  which  gradually  enlarge  in 
consequence  of  the  advancing  maturity  of  their  eggs. 

The  Graafian  follicle  then  consists  of  a  closed  sac,  the  external  wall 
of  which,  though  translucent,  has  a  fibrous  texture,  and  is  well  supplied 
with  blood-vessels.  This  fibrous  and  vascular  wall  is  distinguished  by 
the  name  of  the  "  vesicular  membrane."  It  is  not  very  firm  in  texture, 
and  if  roughly  handled  is  easily  ruptured. 

*  Annales  des  Sciences  Naturelles,  Paris,  Aoilt— Septembre,  1844. 


602  REPRODUCTION. 

The  vesicular  membrane  is  lined  throughout  by  a  layer  of  granular 
cells,  which  form  for  it  a  kind  of  epithelium.  This  layer  is  termed 
the  membrana  granulosa.  It  adheres  but  slightly  to  the  vesicular  mem- 
brane, and  may  easily  be  detached  by  manipulation  before  the  follicle 
is  opened,  when  it  appears .  mingled,  in  the  form  of  light  flakes  and 
shreds,  with  the  serous  fluid  of  the  follicle. 

At  the  most  superficial  part  of  the  Graafian  follicle  the  membrana 
granulosa  is  thicker  than  elsewhere.  Its  cells  are  here  accumulated,  in 
a  kind  of  mound  or  "  heap,"  which  has  received  the  name  of  the  cumu- 
lus proligerus.  It  is  also  called  the  discus  proligerus,  because  the 
thickened  mass,  when  viewed  from  above,  has  a  circular  or  disk-like 
form.  In  the  centre  of  the  discus  proligerus  the  egg  is  imbedded.  It 
is  accordingly  always  situated  at  the  most  superficial  portion  of  the 
follicle,  nearest  the  surface  of  the  ovary. 

As  the  period  approaches  for  the  discharge  of  the  egg,  the  Graafian 
follicle  becomes  more  vascular,  and  enlarges  by  an  increased  exudation 
into  its  cavity.  It  then  begins  to  project  from  the  surface  of  the  ovary, 
still  covered  by  the  albugineous  tunic  and  its  peritoneal  investment. 
(Pig.  167.)  The  accumulation  of  fluid  exerts  such  a  pressure  from 
within,  that  the  albugineous  tunic  and  peritoneum  gradually  yield 


GRAAFIAN  FOLLICLE,  near  the  period  of  rupture.— a.  Vesicular  membrane,  b.  Membrana  granu- 
losa. c.  Cavity  of  follicle,  d.  Egg.  e.  Peritoneal  surface.  /.  Tunica  albuginea.  g,  g.  Tissue  of 
the  ovary. 

before  it ;  until  the  Graafian  follicle  protrudes  from  the  ovary  as  a 
tense,  rounded,  translucent  vesicle,  in  which  fluctuation  can  be  perceived 
on  applying  the  fingers  to  its  surface.  Finally,  the  process  of  effusion 
and  distention  still  going  on,  the  wall  of  the  follicle  gives  way  at  its 
most  prominent  portion,  and  the  contained  fluid  is  expelled  by  the 
elastic  reaction  of  the  ovarian  tissue,  carrying  with  it  the  egg,  entangled 
in  a  portion  of  the  membrana  granulosa. 

The  rupture  of  the  Graafian  follicle  is  accompanied,  in  some  instances, 
by  hemorrhage  from  its  inner  surface,  by  which  it  is  filled  with  blood. 
This  occurs  in  the  human  species,  in  the  pig,  and  to  some  extent  in 
several  other  animals.  Sometimes,  as  in  the  cow,  where  there  is  no 
immediate  hemorrhage,  the  Graafian  follicle  collapses  at  the  time  of 


OVTJLATION    AND    MENSTRUATION. 


603 


FIG.  168. 


rupture ;  after  which  a  slight  exudation,  more  or  less  tinged  with  blood, 
is  poured  out  in  the  course  of  a  few  hours. 

This  process  occurs  in  one  or  more  follicles  at  a  time,  according  to 
the  number  of  young  to  be  produced.  In  the  bitch  and  the  sow, 
where  each  litter  consists  of  from  five  to  twenty  young,  a  similar  num- 
ber of  eggs  ripen  and  are  discharged  at  each  period.  In  the  mare,  the 
cow,  and  the  human  female,  where  there  is  usually  but  one  foetus  at  a 
birth,  the  eggs  are  matured  singly,  and  the  Graafian  follicles  ruptured, 
one  by  one,  at  successive  periods  of  ovulation. 

4.  The  ripening  and  discharge 
of  the  egg  are  accompanied  by  a 
peculiar  condition  of  the  general 
system,  known  as  "rutting,"  or 
"  csstruation."  The  congestion 
and  functional  activity  shown  by 
the  ovaries,  at  each  period  of  ovu- 
lation, extend  to  the  other  genera- 
tive organs,  producing  in  them 
more  or  less  excitement,  according 
to  the  species  of  animal.  Usually 
there  is  vascular  congestion  of  the 
entire  generative  apparatus.  The 
secretions  of  the  vagina  and  neigh-  ^^,^^S^S!^^ 
boring  parts  are  increased  in  quan-  the  membrana  granuiosa. 
tity  and  altered  in  quality.  In  the 

bitch,  the  vaginal  mucous  membrane  becomes  red  and  tumefied,  and  pours 
out  a  secretion  more  or  less  tinged  with  blood,  and  possessing  a  peculiar 
odor,  which  appears  to  attract  the  male.  An  unusual  tumefaction  and 
redness  of  the  vagina  and  vulva  are  also  perceptible  in  the  rabbit ;  and 
in  some  apes  there  is  not  only  a  bloody  discharge  from  the  vulva,  but 
engorgement  and  infiltration  of  the  neighboring  parts,  extending  to 
the  buttocks,  the  thighs,  and  the  under  part  of  the  tail.* 

The  system  at  large  is  also  affected.  In  the  cow,  the  approach  of  an 
osstrual  period  is  marked  by  unusual  restlessness.  The  animal  partially 
loses  her  appetite.  She  frequently  stops  browsing,  looks  about  un- 
easily, runs  from  one  side  of  the  field  to  the  other,  and  then  recom- 
mences feeding,  to  be  again  disturbed  in  a  similar  manner  after  a  short 
interval.  The  motions  are  rapid  and  nervous,  and  the  hide  rough  and 
disordered,  indicating  the  presence  of  some  special  excitement.  After, 
oostruation  is  fully  established,  the  vaginal  secretions  continue  for  one 
or  two  days  unusually  abundant ;  after  which  the  symptoms  subside, 
and  the  animal  returns  to  her  usual  condition. 

In  these  animals  the  female  will  allow  the  approach  of  the  male  only 
during  or  immediately  after  the  oestrual  period ;  that  is,  when  the  egg 
is  recently  discharged,  and  ready  for  impregnation.  At  other  times, 


Pouchet,  ThSorie  positive  de  1'ovulation.     Paris,  1847,  p.  230. 


604  REPRODUCTION. 

when  sexual  intercourse  would  be  fruitless,  the  instinct  of  the  animal 
leads  her  to  avoid  it ;  and  the  concourse  of  the  sexes  accordingly  cor- 
responds in  time  with  the  maturity  of  the  egg  and  its  aptitude  for 
fecundation. 

Menstruation. 

In  the  human  female,  the  periodical  excitement  of  the  generative 
apparatus  is  marked  by  a  group  of  phenomena  known  as  menstruation, 
which  are  of  sufficient  importance  to  be  described  by  themselves. 

During  infancy  and  childhood  the  sexual  system  is  inactive.  No 
eggs  are  discharged  from  the  ovaries,  and  no  external  phenomena  show 
themselves,  connected  with  the  reproductive  function. 

But  at  the  age  of  fourteen  or  fifteen  years,  a  change  becomes  visible. 
The  outlines  of  the  body  grow  more  rounded,  the  breasts  increase  in 
size,  and  the  entire  aspect  undergoes  a  peculiar  alteration,  dependant  on 
the  approach  of  maturity.  At  the  same  time  a  discharge  of  blood  takes 
place  from  the  generative  passages,  accompanied  by  some  disturbance 
of  the  general  system,  and  the  female  is  then  known  to  have  arrived 
at  the  period  of  puberty. 

Afterward,  the  discharges  recur  at  intervals  of  four  weeks ;  and,  from 
their  correspondence  in  time  with  successive  lunar  months,  they  are 
designated  as  the  "menses"  or  "menstrual  periods."  These  periods 
are  usually  regular  in  recurrence,  from  their  first  appearance,  until  about 
the  age  of  forty-five  years.  During  this  time  the  female  is  capable  of 
bearing  children,  and  sexual  intercourse  is  liable  to  be  followed  by 
pregnancy.  After  the  forty-fifth  year,  the  periods  first  become  irreg- 
ular, and  then  cease ;  their  final  disappearance  being  an  indication  that 
pregnancy  cannot  again  take  place. 

Between  the  ages  of  fifteen  and  forty-five  years,  the  regularity  of 
the  menstrual  periods  indicates  to  a  great  extent  the  individual  apti- 
tude for  impregnation.  All  causes  of  ill  health  which  derange  men- 
struation are  also  apt  to  interfere  with  pregnancy  ;  and  women  whose 
menses  are  regular  are  more  likely  to  become  pregnant,  after  sexual 
intercourse,  than  those  in  whom  the  periods  are  absent  or  irregular. 

When  pregnancy  takes  place,  however,  the  menses  are  suspended 
during  its  continuance.  They  usually  remain  absent,  after  delivery, 
until  the  end  of  lactation,  Avlien  they  recommence,  and  recur  at  regular 
intervals,  as  before. 

When  the  menstrual  period  is  about  to  come  on,  the  female  is  usually 
affected  with  some  degree  of  discomfort  and  lassitude,  a  sense  of  weight 
in  the  pelvis,  and  a  more  or  less  disinclination  to  society.  These  symp- 
toms are  in  some  instances  slightly  pronounced,  in  others  more  distinct. 
A  discharge  of  vaginal  mucus  then  begins  to  take  place,  soon  becoming 
yellowish  or  rusty-brown  in  color,  from  the  admixture  of  blood;  and 
by  the  second  or  third  day  it  has  the  appearance  of  nearly  pure  blood. 
The  unpleasant  sensations,  at  first  manifest,  then  usually  subside;  and 
the  discharge,  after  continuing  for  two  or  three  (lavs  longer,  grows 
more  scanty.  Its  red  color  diminishes  in  intensity,  becoming  brown- 


OVULATION    AND    MENSTRUATION.  605 

ish  or  rusty,  until  it  finally  disappears,  and  the  process  comes  to  an 
end. 

The  menstrual  periods  of  the  human  female  correspond  with  those 
of  cestruation  in  animals.  Like  them,  they  are  absent  in  the  immature 
condition,  and  begin  only  at  the  time  of  puberty,  when  the  aptitude 
for  impregnation  commences.  Like  them,  they  recur  during  the  child- 
bearing  period  at  regular  intervals,  and  are  liable  to  the  same  inter- 
ruption by  pregnancy.  Finally,  their  disappearance  corresponds  with 
the  cessation  of  fertility. 

The  periods  of  cestruation,  in  many  animals,  are  accompanied  with . 
an  unusual  discharge  from  the  generative  passages,  frequently  more . 
or  less  tinged  with  blood.     In  the  human  female  the  bloody  discharge, 
though  more  abundant,  differs  only  in  degree  from  that  which  exists 
in  other  instances. 

But  the  most  complete  evidence  that  the  menstrual  periods  coincide 
with  ovulation,  is  derived  from  direct  observation.  A  sufficient  num- 
ber of  instances  have  been  recorded  to  show  that  at  the  time  of  men- 
struation a  Graafian  follicle  becomes  enlarged,  ruptures,  and  discharges 
its  egg.  Cruikshank*  noticed  such  a  case  in  179T.  Negrierf  relates 
two  instances  in  which,  after  sudden  death  during  menstruation,  a 
bloody  and  ruptured  Graafian  follicle  was  found  in  the  ovary.  Bis- 
choff  J  speaks  of  four  similar  cases,  in  three  of  which  the  follicle  was 
just  ruptured,  and  in  the  fourth  distended,  prominent,  and  ready  to 
burst.  Coste§  met  with  several  of  the  same  kind.  Michel  ||  found  a 
follicle  ruptured  and  filled  with  blood  in  a  woman  who  was  executed 
for  murder  while  the  menses  were  present.  Two  instances  are  reported 
by  Letheby,T  in  one  of  which  he  succeeded  in  finding  the  ovum  in  the 
corresponding  Fallopian  tube.  We  have  also  met  with  two  instances 
of  Graafian  follicles  freshly  ruptured  and  filled  with  blood,  in  women 
who  died  during  or  immediately  after  menstruation. 

Ovulation,  accordingly,  in  the  human  female,  accompanies  and  forms 
a  part  of  menstruation.  As  the  menstrual  period  comes  on,  a  congestion 
takes  place  throughout  the  generative  apparatus  ;  in  the  Fallopian  tubes 
and  the  uterus,  as  well  as  in  the  ovaries  and  their  contents.  One  of  the 
Graafian  follicles  is  especially  the  seat  of  vascular  excitement.  It  be- 
comes distended  by  the  accumulation  of  fluid  in  its  cavity,  projects  from 
the  surface  of  the  ovary,  and  is  finally  ruptured ;  the  process  taking 
place  essentially  as  in  mammalian  animals. 

It  is  not  certain  at  what  precise  time  during  the  menstrual  flow  the 
rupture  of  the  follicle  takes  place.  According  to  Bischoff,  Pouchet,  and 
Raciborski,  it  usually  happens,  not  at  the  commencement,  but  toward 

*  Philosophical  Transactions.     London,  1797,  p.  135. 

f  Kecherches  sur  lea  Ovaires.     Paris,  1840,  p.  78. 

J  Annales  des  Sciences  Naturelles.     Paris,  Aoftt,  1844. 

%  Histoire  du  DeVeioppment  des  Corps  Organises.     Paris,  1847,  tome  i.,  p.  221. 

||  American  Journal  of  the  Medical  Sciences.     Philadelphia,  July,  1848. 

fl  Philosophical  Transactions.     London,  1852,  p.  57. 


606  REPRODUCTION. 

the  termination  of  the  period.  According  to  Coste,*  it  is  sometimes 
earlier,  sometimes  later.  So  far  as  we  can  determine,  its  precise  period 
is  not  invariable.  Like  the  menses  themselves,  it  may  be  hastened  or 
retarded  according  to  circumstances ;  but  it  always  occurs  in  connec- 
tion with  the  menstrual  flow,  and  constitutes  the  most  important  part 
of  the  process  in  regard  to  reproduction. 

The  egg,  when  discharged  from  the  ovary,  enters  the  Hmbriated 
extremity  of  the  Fallopian  tube,  and  commences  its  passage  toward 
the  uterus.  The  mechanism  by  which  it  finds  its  way  into  and  through 
the  Fallopian  tube  in  quadrupeds  and  man  is  different  from  that  in 
birds  and  reptiles.  In  the  latter,  the  bulk  of  the  eggs  is  sufficient  to 
distend  the  oviduct ;  and  the  mass,  embraced  by  the  muscular  wall 
of  the  canal,  is  carried  downward  by  peristaltic  action.  In  mamma- 
lians, on  the  other  hand,  the  egg  is  microscopic  in  size.  The  wide 
extremity  of  the  Fallopian  tube,  directed  toward  the  ovary,  is  lined 
with  ciliated  epithelium  ;  and  the  movement  of  the  cilia,  which  is  from 
the  ovary  toward  the  uterus,  produces  a  kind  of  vortex,  by  which  the 
egg  is  conducted  into  the  narrow  portion  of  the  tube,  and  thence  down- 
ward to  the  uterus. 

Accidental  causes  may  sometimes  disturb  the  passage  of  the  egg. 
It  may  be  arrested  at  the  surface  of  the  ovary,  and  thus  fail  to  enter 
the  Fallopian  tube.  If  it  be  fecundated  and  go  on  to  partial  develop- 
ment in  this  situation,  it  gives  rise  to  "ovarian  pregnancy."  It  may 
escape  from  the  fimbriated  extremity  of  the  Fallopian  tube  into  the 
peritoneal  cavity,  and  form  attachments  to  a  neighboring  organ,  causing 
"  abdominal  pregnancy ;"  or  finally  it  may  stop  in  some  part  of  the 
Fallopian  tube,  and  thus  give  origin  to  "  tubal  pregnancy." 

The  egg,  immediately  after  its  discharge  from  the  ovary,  is  ready 
for  impregnation.  If  sexual  intercourse  take  place  about  that  time, 
the  egg  and  the  spermatozoa  meet  in  some  part  of  the  female  genera - 
tive  passages,  and  fecundation  is  accomplished.  It  appears  from  the 
observations  of  Bischoif,  Coste,  and  Barry  f  upon  rabbits,  that  the 
contact  of  the  egg  and  the  spermatozoa  may  take  place  either  in  the 
uterus  or  the  Fallopian  tubes,  or  on  the  surface  of  the  ovary.  If,  on 
the  other  hand,  there  be  no  sexual  coitus,  the  egg  passes  the  Fallopian 
tube  unimpregnated,  loses  its  vitality  after  a  time,  and  is  carried  away 
with  the  uterine  secretions. 

For  this  reason  sexual  intercourse  is  most  liable  to  be  followed  by 
pregnancy  when  occurring  at  or  soon  after  the  menstrual  epoch. 
Before  its  discharge,  the  egg  is  immature  and  unfit  for  impregnation ; 
and  some  days  afterward,  it  loses  its  freshness  and  vitality.  The  exact 
length  of  time,  preceding  and  following  the  menses,  during  which  im- 
pregnation is  possible,  has  not  been  ascertained.  The  spermatozoa, 
on  the  one  hand,  retain  their  vitality  for  an  unknown  period  after 
coition,  and  the  egg  for  an  unknown  period  after  its  discharge.  These 

*  Histoirt-  dii  D6veloppment  des  Corps  Organises.     Paris,  1847,  tome  i.,  p.  221. 
f  Philosophical  Transactions.     London,  1839,  p.  315. 


OVULATION    AND    MENSTRUATION.  607 

occurrences  may  either  precede  or  follow  each  other  within  certain 
limits,  and  impregnation  may  still  take  place ;  but  the  precise  extent 
of  these  limits  is  undetermined,  and  is  probably  more  or  less  variable 
in  different  individuals. 

Lastly,  there  are  exceptional  cases  in  which  fertility  exists  without 
a  menstrual  flow,  and  menstruation  without  ovulation.  If  we  regard 
the  rupture  of  an  ovarian  follicle  and  hemorrhage  from  the  uterus,  in 
menstruation,  as  two  phenomena  normally  coincident,  excited  by  a 
common  cause,  and  subservient  to  the  same  general  function,  we  must 
still  recognize  the  possibility  of  either  one  being  deranged  indepen- 
dently of  the  other.  Various  authors  (Churchill,  Reid,  Yelpeau)  have 
related  instances  of  fruitful  women  in  whom  the  menses  were  scanty 
and  irregular,  or  even  absent.  The  menstrual  flow  is  habitually  scanty 
in  some  individuals,  and  abundant  in  others.  Such  variations  depend 
on  the  vascular  activity  of  the  system  at  large,  or  of  the  uterine  organs 
in  particular ;  and  though  the  bloody  discharge  is  usually  an  index 
of  the  aptitude  of  these  organs  for  impregnation,  it  is  not  invariably 
so.  Provided  a  mature  egg  be  discharged  from  the  ovary,  pregnancy 
is  possible  although  the  menstrual  flow  be  absent. 

On  the  other  hand  we  have  met  with  a  fully  authenticated  instance* 
in  which  menstruation  recurred  regularly  for  several  months  without 
the  rupture  of  a  Graafian  follicle ;  and  twelve  cases  have  been  collected 
by  Goodman  f  in  which  menstruation  continued  notwithstanding  the 
removal  of  both  ovaries,  in  the  adult,  by  ovariotomy.  But  where  the 
ovaries  are  congenitally  undeveloped,  menstruation  is  also  absent,  and 
the  sexual  system  inactive. 

The  blood  which  escapes  during  the  menstrual  flow  is  supplied  by 
the  uterine  mucous  membrane.  After  death  during  menstruation,  the 
internal  surface  of  the  uterus  is  found  smeared  with  a  sanguineous 
fluid,  which  may  be  traced  through  the  uterine  cervix  into  the  vagina. 
The  Fallopian  tubes  are  sometimes  congested,  and  filled  with  a  similar 
bloody  discharge.  The  menstrual  blood  has  also  been  seen  to  exude 
from  the  uterine  orifice  in  cases  of  procidentia  uteri,  as  well  as  in  the 
normal  condition  by  examination  with  the  speculum.  It  is  discharged 
by  a  kind  of  capillary  hemorrhage,  and,  as  a  rule,  does  not  form  a 
visible  coagulum,  owing  to  its  being  exuded  from  many  minute  points, 
and  mingled  with  mucus.  When  poured  out  more  rapidly  and  abun- 
dantly, as  in  menorrhagia,  it  coagulates  in  the  same  manner  as  blood 
from  other  sources.  Its  discharge  is,  at  the  same  time,  the  conse- 
quence and  the  natural  termination  of  the  uterine  congestion. 

*  Transactions  of  the  American  Gynaecological  Society.     Boston,  1878,  vol.  ii., 
p.  136. 
f  Richmond  and  Louisville  Medical  Journal,  December,  1875. 


CHAPTER  V. 

THE  CORPUS  LUTEUM,  AND  ITS  CONNECTION  WITH 
MENSTRUATION  AND  PREGNANCY. 

AFTER  the  rupture  of  a  Graafian  follicle  at  the  menstrual  period, 
there  is  left  in  the  ovary  a  bloody  cavity,  which  is  subsequently 
obliterated  by  a  process  somewhat  similar  to  the  healing  of  an  abscess. 
The  office  of  the  Graafian  follicle  is  to  provide  for  the  formation  and 
growth  of  the  egg  in  the  ovary.  After  the  discharge  of  the  egg,  the 
follicle  has  no  further  function  to  perform  ;  and  it  then  passes  through 
a  process  of  obliteration,  as  an  organ  which  has  become  obsolete. 
While  undergoing  this  change,  it  is  at  one  time  converted  mto  a 
solid,  spheroidal  body,  called  the  corpus  luteum ;  a  name  derived  from 
the  yellow  color  acquired  during  its  formation. 

In  quadrupeds,  the  corpus  luteum  is  characterized  by  peculiarities 
of  size,  color,  growth,  and  disappearance,  which  are  distinctive  for 
each  species ;  although  the  general  course  of  its  formation  and  atrophy 
is  the  same  in  all.  In  the  human  female  it  is  marked  by  a  moderately 
large  size,  a  brilliant  yellow  hue  at  certain  periods  of  its  development, 
and  the  presence  of  blood  in  its  central  cavity,  distinguishable  for  two 
or  three  weeks  after  the  rupture  of  the  follicle.  The  details  of  its 
growth  and  retrocession,  which  follow  a  regular  course  during  the 
normal  recurrence  of  the  menstrual  periods,  are  modified  by  the  ex- 
istence of  pregnancy.  In  the  first  instance,  it  is  known  as  the  corpu* 
luteum  of  menstruation ;  in  the  second  as  the  corpus  luteum  of  preg- 
nancy. 

Corpus  Luteum  of  Menstruation. 

In  the  human  female,  during  menstruation,  at  or  immediately  after 
the  discharge  of  the  egg,  a  somewhat  abundant  hemorrhage  takes  place 
from  the  inner  surface  of  the  Graafian  follicle,  by  which  its  cavity  is 
filled  with  blood.  The  blood  soon  coagulates,  as  it  would  if  cxtrava- 
sated  elsewhere,  and  the  coagulum  remains  enclosed  by  the  walls  of 
the  follicle.  The  opening  by  which  the  egg  has  escaped  is  usually  a 
rounded  perforation,  not  more  than  one  millimetre  in  diameter;  niul 
a  slender  probe,  introduced  through  this  opening,  passes  directly  into 
the  cavity  of  the  follicle.  If  the  follicle  be  opened  at  this  time  by  a 
longitudinal  incision  through  the  ovary  (Fig.  169),  it  will  be  seen  to 
form  a  spheroidal  cavity,  between  one  and  two  centimetres  in  diameter, 
containing  the  soft,  recent,  dark  colored  coagulum.  The  coagulum  has 
uo  organic  connection  with  the  walls  of  the  follicle,  but  lies  loose  in 

608 


THE    COKPUS    LUTEUM. 


609 


FIG.  169. 


ruptured  during  menstru- 
ation, and  filled  with  co- 
agulated blood;  longitudi- 
nal section. — a.  Tissue  of 
the  ovary,  containing  un- 
ruptured  Graafian  follicles. 
b.  Vesicular  membrane  of 
the  ruptured  follicle,  c. 
Point  of  rupture. 


its  cavity,  and  may  be  easily  turned  out  with  the  handle  of  a  scalpel. 

It  has  sometimes  a  slight  mechanical  adhesion  to  the  edges  of  the 

lacerated  opening ;  but  there  is  no  continuity  of 

substance  between  them,  and  the  clot  may  be 

everywhere  separated  by  careful  manipulation. 

The  membrane  of  the  vesicle  presents  a  smooth, 

transparent,  and  vascular  internal  surface. 

Soon  afterward  an  important  change  takes 
place,  both  in  the  central  coagulum  and  in  the 
vesicular  membrane. 

The  clot,  which  is  at  first  large,  soft,  and  gelat- 
inous, begins  to  contract ;  and  the  serum  sepa- 
rates from  the  coagulum  proper.  The  serum  is 
absorbed  by  the  neighboring  parts;  and  the  clot, 
accordingly,  grows  smaller  and  denser.  At  the 
same  time  its  coloring  matter  undergoes  the 
usual  changes  which  follow  extravasation,  and 
is  partially  reabsorbed  together  with  the  serum. 
This  second  change  is  somewhat  less  rapid  than 
the  former,  but  a  diminution  of  color  is  usually 
perceptible  in  the  clot,  at  the  expiration  of  two 
weeks  from  the  rupture  of  the  follicle. 

The  vesicular  membrane  at  the  same  time 
takes  on  an  increased  development,  by  which  it  becomes  thickened  and 
convoluted,  and  tends  partially  to  fill  the  cavity  of  the  follicle.  Its 
hypertrophy  and  convolution  commences  earliest  and  proceeds  most 
rapidly  at  the  deeper  part  of  the  follicle.  From  this  point  it  becomes 
thinner  and  less  convoluted  toward  the  surface  of  the  ovary  and  the 
edges  of  the  ruptured  orifice. 

At  the  end  of  three  weeks,  the  hypertrophy  of  the  vesicular  mem- 
brane has  reached  its  maximum.  The  follicle  has  now  become  so  altered 
by  the  growth  above  described,  and  by  the  condensation  of  its  clot,  that 
it  presents  the  appearance  of  a  solid  body  of  new  formation,  and  receives 
the  name  of  "corpus  luteum,"  although  its  yellow  color  is  not  yet  dis- 
tinctly developed.  It  causes  a  perceptible  prominence  on  the  surface 
of  the  ovary,  and  may  be  felt  as  a  rounded  tumor,  in  the  ovarian  tissue, 
nearly  always  somewhat  flattened  from  side  to  side.  It  measures  about 
19  millimetres  in  length  and  about  12  millimetres  in  depth.  On  its 
surface  there  is  a  minute  cicatrix,  the  mark  of  the  original  rupture.  * 

On  cutting  it  open  at  this  time  (Fig.  170),  the  corpus  luteum  is  seen 
to  consist,  as  above  described,  of  a  central  coagulum  and  a  convoluted 
wall.  The  coagulum  is  semi-transparent,  of  a  gray  or  light-greenish 
color,  more  or  less  mottled  with  red.  The  convoluted  wall  is  about 
three  millimetres  thick  at  its  deepest  part,  and  of  an  indefinite  yellow- 
ish or  rosy  hue,  not  very  different  in  tinge  from  the  rest  of  the  ovarian 
tissue.  The  convoluted  wall  and  the  contained  clot  lie  in  contact  with 
each  other,  without  intervening  organic  connection ;  and  they  may  still 

2O 


610 


REPRODUCTION. 


FIG.  170. 


be  readily  separated  by  the  handle  of  a  scalpel  or  the  flattened  end  of  a 
probe.  The  whole  corpus  luteum  may  also  be  stripped  out,  or  enucle- 
ated from  the  ovarian  tissue ;  and  when  extracted  in  this  way,  it  pre- 
sents itself  as  a  spheroidal  or  flattened  mass,  with  a  convoluted  external 

surface  covered  with  remains  of  the  con- 
nective tissue  by  which  it  was  attached  to 
the  substance  of  the  ovary. 

We  have  had  an  opportunity  of  exam- 
ining a  corpus  luteum  of  this  period,  in 
an  ovary  immediately  after  its  removal 
from  the  body  of  the  living  woman.  It 
was  on  the  occasion  of  the  extirpation 
by  Prof.  T.  T.  Sabine,  in  1874,  of  the 
left  ovary  for  obstinate  ovarian  neuralgia, 
from  an  unmarried  woman,  otherwise 
healthy,  25  years  of  age.*  The  last  men- 
strual period  had  terminated  exactly  three 

weeks  before  the  date  of  the  operation, 
HUMAN  OVARY  cut  open,  showing  a  ,  ,    , 

corpus  luteum,  divided  longitudi-    and  a  new  one  commenced  twenty-four 
naiiy ;  three  weeks  after  menstrua-    hours  afterward.     The  extirpated  ovary 

presented  a  perfectly  normal  appearance, 
and  contained  a  corpus  luteum  similar  in 
all  respects  to  that  represented  in  Fig.  170.  Its  convoluted  wall  was 
fully  formed,  without  any  distinctly  marked  yellow  tinge,  and  the  cen- 
tral coagulum  was  partly,  but  not  entirely,  de- 
colorized. The  patient  recovered  without  diffi- 
culty. 

After  the  third  week  from  the  close  of  men- 
struation, the  corpus  luteum  passes  into  a  retro- 
grade condition.  It  diminishes  perceptibly  in 
size,  and  the  central  coagulum  continues  to  be 
absorbed  and  loses  still  farther  its  coloring  mat- 
ter. The  whole  body  undergoes  a  process  of 
atrophy  ;  and  at  the  end  of  the  fourth  week  it  is 
less  than  10  millimetres  in  its  longest  diameter 
(Fig.  171).  The  external  cicatrix  may  still  be 
seen,  as  well  as  the  point  where  the  central  co- 
agulum lies  in  contact  with  the  peritoneal  sur- 
face. There  is  still  no  organic  connection  be- 
tween the  coagulum  and  the  convoluted  wall ; 
but  the  condensation  of  the  clot  and  the  closer 
folding  of  the  wall  prevent  the  separation  of  the  two  being  so  easily 
accomplished  as  before.  The  entire  corpus  luteum  may  still  be  extracted 
from  its  Iji-il  in  the  ovarian  tissue. 

The  color  of  the  convoluted  wall,  during  this  stage,  instead  of  fading, 


tion.    From  a  girl,  twenty  years  of 
age,  dead  of  haemoptysis. 


FIG.  171. 


HUMAN  OVAUY, 

<-orpu>  luteum.  four 

after  menstruation  ;    from 

a  woman  dead  of  apoplexy. 


I  York  Mrdiral  Journal,  January,  1875,  p.  37. 


THE    CORPUS    LUTEUM.  611 

like  that  of  the  fibrinous  coagulum,  increases  in  intensity.  From  an 
indefinite  yellowish  or  rosy  hue,  it  gradually  becomes  a  decided  yellow. 
This  change  is  produced  simultaneously  with  a  kind  of  fatty  degenera- 
tion of  its  tissue ;  which  presents  at  this  time,  under  the  microscope,  a 
considerable  deposit  of  oil  globules.  At  the  end  of  the  fourth  week, 
the  alteration  in  hue  is  complete ;  and  the  outer  wall  of  the  corpus 
luteum  is  then  of  a  clear  chrome-yellow  color,  by  which  it  is  readily 
distinguishable  from  the  neighboring-  parts. 

After  this  period,  degeneration  goes  on  rapidly.  The  clot  becomes 
dense  and  shrivelled,  and  is  converted  into  a  minute,  stellate,  white,  or 
reddish-white  cicatrix.  The  yellow  wall 
grows  softer  and  more  friable,  and  exhibits 
less  distinctly  the  marking  of  its  convolutions. 
At  the  same  time  its  surface  becomes  con- 
founded with  the  central  coagulum  on  the  one 
hand,  and  with  the  neighboring  parts  on  the 
other,  so  that  it  is  no  longer  possible  to  sepa- 
rate them  fairly  from  each  other.  At  the 
end  of  eight  or  nine  weeks  (Fig.  172)  the 
whole  is  reduced  to  an  insignificant,  yellowish, 
cicatrix-like  spot,  measuring  about  six  milli- 
metres in  its  longest  diameter,  in  which  the  . 

.    .  HUMAN  OVARY,  showing  a  cor- 

Origmal  texture  Of  the  COrpUS    luteum  Can   be         pus  luteum.  nine  weeks  after 

recognized  only  by  the  peculiar  folding  and      menstruation;  from  a  gM  dead 

.  of  tubercular  meningitis. 

coloring  or  its  constituent  parts.     Afterward 

its  atrophy  goes  on  more  slowly,  and  seven  or  eight  months  may  some- 
times elapse  before  its  complete  disappearance. 

The  size  of  the  corpus  luteum  depends  on  the  quantity  of  blood 
exuded  into  the  follicle  at  the  time  of  its  rupture,  and  on  the  more  or 
less  active  growth  of  its  convoluted  wall.  Both  these  conditions  may 
no  doubt  vary  in  different  cases,  according  to  the  general  bodily  devel- 
opment, and  the  size  and  vascularity  of  the  ovaries  in  particular.  In 
healthy  women  the  weight  of  the  ovaries,  which  is,  on  the  average, 
five  grammes  each,  varies  frequently  twenty  per  cent,  above  or  below 
this  standard ;  and  even  in  the  same  individual  the  right  and  left  ovaries 
are  seldom  of  the  same  size ;  usually  differing  from  each  other  by  at 
least  ten  per  cent.  It  is  therefore  impossible  to  fix  an  invariable 
standard  of  size  for  the  corpus  luteum,  corresponding  with  its  period 
of  development.  But  it  nevertheless  follows,  during  the  greater  part 
of  the  intermenstrual  period,  a  general  course  of  enlargement,  succeeded 
by  a  process  of  atrophy.  The  following  list  gives  its  weight  as  actually 
observed*  in  eight  cases  in  which  the  date  of  menstruation  was  known. 

*  Transactions  of  the  American  Gynecological  Society.  Boston,  1878,  vol.  ii.,  p. 
130. 


612  REPRODUCTION. 

WEIGHT  OF  THE  CORPUS  LUTETM. 

Milligrammes. 

1.  Two  days  after  menstruation 380 

2.  Nine  days  after                         430 

3.  Ten  days  after                          810 

4.  Fifteen  to  twenty  days  after  menstruation      .         .         .  1230 

5.  Twenty  days  after  menstruation 1200 

6.  Six  weeks  after                "                90 

7.  Ten  weeks  after                               20 

8.  Eleven  weeks  after         "                15 

The  corpus  luteum,  accordingly,  is  a  formation  which  results  from 
the  obliteration  of  a  ruptured  Graafian  follicle.  It  is  produced  during 
the  intermenstrual  period,  and  occupies  the  substance  of  the  ovary, 
immediately  beneath  the  superficial  cicatrix  which  marks  the  site  of 
the  rupture.  After  acquiring  its  maximum  size  about  the  end  of  the 
third  week  it  passes  into  the  retrograde  condition  and  soon  becomes 
obsolete ;  while  a  new  body,  of  similar  structure,  is  produced  from  the 
rupture  of  another  Graafian  follicle.  In  an  ordinary  intermenstrual 
period,  therefore,  the  ovaries  contain,  as  a  rule,  one  corpus  luteum  of 
preponderating  size,  and  in  addition  several  which  are  more  or  less 
obsolete.  Four,  five,  six,  and  even  eight  corpora  lutea  may  thus  be 
found  in  the  ovaries  at  the  same  time,  perfectly  distinguishable  by 
their  texture,  though  very  small,  and  for  the  most  part  in  a  state  of 
advanced  retrogression.  As  they  finally  disappear,  one  after  the  other, 
their  number  no  longer  corresponds  with  that  of  the  Graafian  follicles 
which  have  been  ruptured. 

Corpus  Luteum  of  Pregnancy. 

Since  the  process  above  described  occurs  at  each  menstrual  period, 
the  presence  of  a  corpus  luteum  is  no  indication  that  pregnancy  has 
existed,  but  only  that  a  Graafian  follicle  has  been  ruptured  and  its 
contents  discharged.  Nevertheless,  when  pregnancy  takes  place,  the 
history  of  the  corpus  luteum  is  different  in  some  respects  from  that 
which  follows  an  ordinary  menstruation. 

The  distinction  between  the  two  kinds  of  corpora  lutea  is  not  an 
essential  or  fundamental  difference ;  since  they  both  originate  in  the 
same  way,  and  are  composed  of  the  same  structures.  It  depends  on 
the  difference  in  rapidity  and  degree  of  their  development.  While  the 
corpus  luteum  of  menstruation  passes  rapidly  through  its  stages,  ami 
is  soon  reduced  to  a  condition  of  atrophy,  that  of  pregnancy  continues 
its  development  for  a  longer  time,  attains  a  larger  size  and  firmer  organ- 
ization, and  disappears  at  a  later  period. 

The  variation  of  the  corpus  luteum  in  pregnancy  is  caused,  no  doubt, 
by  the  condition  of  the  uterus.  This  organ  exerts  a  wide  influence,  in 
the  state  of  gestation,  on  many  parts  of  the  system.  The  stomach 
becomes  irritable,  the  appetite  is  capricious,  and  even  the  mental  HIM! 
moral  qualities  are  more  or  less  affected.  The  ovaries  feel  this  influence 


THE    CORPUS    LUTEUM. 


613 


FIG.  173. 


to  such  a  degree  that  ovulation  is  arrested,  and  no  more  Graafian  folli- 
cles are  ruptured,  during  the  whole  term  of  pregnancy.  It  is  not  sur- 
prising that  the  growth  of  the  corpus  luteum  should  be  modified  from 
the  same  cause. 

For  the  first  three  weeks  of  its  formation  the  corpus  luteum  presents 
the  same  features  in  the  impregnated  as  in  the  unimpregnated  condition. 
But  after  that  time  a  difference  becomes  manifest.  Instead  of  commenc- 
ing a  retrograde  course  during  the  fourth  week,  it  continues  its  develop- 
ment. The  external  wall  grows  thicker  and  more  convoluted.  Its  color 
changes,  as  previously  described,  to  a  bright  yellow ;  and  it  contains  a 
deposit  of  fatty  matter  in  the  form  of  microscopic  globules. 

By  the  end  of  the  second  month  of  pregnancy,  the  corpus  luteum  has 
increased  to  22  millimetres  in  length  by  12  or  13  millimetres  in  depth. 
The  central  coagulum  has  be- 
come nearly  decolorized,  and 
presents  the  appearance  of  a 
fibrinous  deposit.  Sometimes 
a  part  of  the  serum,  as  it  sepa- 
rates from  the  clot,  accumulates 
in  the  centre  of  the  mass,  as  in 
Fig.  113,  forming  a  little  cav- 
ity filled  with  clear  fluid  and 
inclosed  by  a  fibrinous  layer, 

the  remains  Of  the  Solid  portion     CORPUS  LUTEUM  of  pregnancy,  at    the    end  of  the 

of  the  clot.     The  existence  of 

such  a  cavity,  however,  is  only 

occasional.     More  frequently,  the  fibrinous  clot  is  solid  throughout,  all 

the  serum  being  absorbed  by  the  surrounding  parts. 

During  the  third  and  fourth  months,  the  enlargement  of  the  corpus 
luteum  continues  ;  and  at  the  end 
of  that  time  it  may  measure  22 
millimetres  in  length  by  18  or  19 
millimetres  in  depth.  Its  flat- 
tened form  is  very  manifest,  so 
that,  in  a  longitudinal  section,  it 
may  present  a  nearly  circular  out- 
line, as  in  Fig.  IT 4,  while  in  a 
transverse  section  its  figure  is 
a  narrow  oval.  The  convoluted 
wall  is  still  more  highly  de- 
veloped than  before,  having  a 
thickness,  at  its  deepest  part,  of 
nearly  5  millimetres.  Its  color, 
however,  has  already  begun  to 
fade,  assuming  a  dull  yellowish 
tinge.  The  central  coagulum,  perfectly  colorless  and  fibrinous,  is  often 
so  much  flattened  laterally  that  it  is  hardly  2  millimetres  in  thickness. 


second  month;  from  a  woman  dead  from  induced 
abortion. 


FIG.  174. 


CORPUS  LUTEUM  of  pregnancy,  at  the  end  of  the 
fourth  month ;  from  a  woman  dead  by  poison. 


REPRODUCTION. 

The  other  relations  between  different  parts  of  the  structure  remain  the 
same. 

The  corpus  luteum  has  now  attained  its  maximum  of  development, 
and  continues  without  very  perceptible  alteration  during  the  fifth  and 
sixtli  months.  It  then  begins  to  retrograde,  diminishing  in  size  during 
the  seventh  and  eighth  months.  Its  external  wall  becomes  still  more 
faded,  changing  to  a  faint  yellowish-white  color,  not  unlike  that  pre- 
at  the  end  of  the  third  week.  It  is  thick,  soft,  and  elastic,  and 
numerous  slender  blood-vessels  can  be  seen 
FIG.  17"..  penetrating  from  without  into  the  interstices 

of  its  convolutions.  Its  central  coagulum  is  re- 
duced to  the  condition  of  a  whitish  radiated 
cicatrix. 

Its  atrophy  continues  during  the  ninth  month. 
At  the  termination  of  pregnancy  (Fig.  175)  it 
is  reduced  to  12  or  13  by  10  millimetres  in  diam- 
eter, and  its  weight  to  about  500  milligrammes. 
It  is  of  a  faint  indefinite  hue,  but  little  con- 
trasted with  that  of  the  surrounding  tissue. 
The  central  cicatrix  is  very  small,  and  appears 
only  as  a  thin  whitish  lamina,  with  radiating 
processes.  The  whole  mass  is  still  firm  to  the 
f^  "^  touch,  and  readily  distinguishable,  both  from  its 

CORPUS  Lr-i  i  :iM,,f  pregnancy,  size    and    texture,  as  a  prominent   feature   in 
a  term,  from  a  woman  dead  tjje  ovarian  tissue.     The  convoluted  structure 

in  delivery  from  rupture  of 

the  uterus.  of  the  external  wall   is  very   perceptible,   and 

the  point  of  rupture,  with   its  peritoneal  cica- 
trix, distinctly  visible. 

After  delivery,  the  corpus  luteum  rapidly  retrogrades.  At  the  end 
of  eight  days  it  usually  weighs  less  than  300  milligrammes,  and  in 
about  two  months  its  color  is  no  longer  distinguishable,  although  indi- 
cations of  its  convoluted  structure  may  still  be  discovered  by  close 
examination.  These  traces  of  its  existence  remain  for  a  long  time 
afterward,  more  or  less  concealed  in  the  ovarian  tissue  ;  being  some- 
times perceptible  so  late  as  nine  and  a  half  months  after  delivery.  They 
finally  disappear  entirely,  together  with  the  external  cicatrix  which 
marked  their  situation. 

During  pregnancy,  owing  to  the  suspension  of  ovulation  and  the 
quiescence  of  the  Graafian  follicles,  no  new  corpora  lutea  are  produced  ; 
and  as  those  which  were  formed  before  the  period  of  conception  fade 
and  dUappear,  UK"  corpus  luteum  which  marks  the  occurrence  of  preg- 
nancy after  a  time  exists  alone  in  the  ovary. 

In  twin  or  triplet  pregnancies  we  should,  of  course,  find  a  corre- 
spondin.ir  nui niter  of  corpora  lutea  in  the  ovaries;  and  it  is  evident 
that  two  Graafian  follicles  might  rupture  simultaneously  at  the  time 
of  conception,  and  but  one  of  the  eggs  become  impregnated  or  roach 
maturity.  In  that  case  there  might  be  one  foetus  in  the  uterus  and 
two  corpora  lutea  in  the  ovaries.  Hut  in  such  instances  both  corpora 


THE    CORPUS    LtTTEUM. 


615 


lutea  would  be  manifestly  of  the  same  age  and  development,  and 
neither  of  them  would  resemble  the  retrograde  structures  habitually 
found  during  menstruation. 

After  lactation,  the  ovaries  resume  their  ordinary  function.  The 
Graafian  follicles  mature  and  rupture  as  before,  and  new  corpora  lutea 
follow  each  other  in  alternate  development  and  disappearance. 

The  corpus  luteum  of  menstruation,  therefore,  differs  from  that  of 
pregnancy  in  development  and  duration.  While  the  former  passes 
through  all  the  important  phases  of  its  growth  and  decline  in  a  period 
of  two  months,  the  latter  lasts  from  nine  to  ten  months,  and  presents, 
during  a  great  portion  of  the  time,  a  larger  size  and  more  solid  organ- 
ization. Even  in  the  corpus  luteum  of  pregnancy,  however,  the  bright 
yellow  color,  which  is  so  striking  a  feature,  is  only  temporary ;  not 
making  its  appearance  till  about  the  end  of  the  fourth  week,  and  again 
disappearing  after  the  sixth  month. 

The  following  table  contains,  in  a  condensed  form,  the  characters  of 
the  corpus  luteum,  in  menstruation  and  pregnancy,  at  different  periods 
of  its  development : 


CORPUS  LUTEUM  OF  MENSTRUATION.   CORPUS  LUTEUM  OF  PREGNANCY. 


At  the  end  of 
three  weeks. 
One  month. 

Two  months. 


Four  months. 


Six  months. 


Nine  months. 


Twelve  by  nineteen  millimetres  in  diameter ;  central  clot  red- 
dish; convoluted  wall  pale. 


Smaller ;  convoluted  wall  bright 
yellow  ;  clot  still  reddish. 

Reduced  to  the  condition  of  an 
insignificant  cicatrix. 


Absent  or  unnoticeable. 


Absent. 


Absent. 


Larger ;  convoluted  wall  bright 
yellow ;  clot  still  reddish. 

Twelve  by  twenty-two  milli- 
metres in  diameter;  convo- 
luted wall  bright  yellow;  clot 
perfectly  decolorized. 

Eighteen  by  twenty-two  milli- 
metres in  diameter;  clot  pale 
andfibrinous;  convoluted  wall 
dull  yellow. 

Still  as  large  as  at  the  end  of 
the  second  month.  Clot  fibri- 
nous.  Convoluted  wall  paler. 

Ten  by  thirteen  millimetres  in 
diameter;  central  clot  con- 
verted into  a  radiating  cic- 
atrix; external  wall  still 
thick  and  convoluted,  but 
without  any  bright  yellow 
color. 


CHAPTER  VI. 

DEVELOPMENT  OF  THE  IMPREGNATED  EGG-SEGMEN- 
TATION   OF    THE    VITELLUS- BLASTODEEM- 
FOIiMATION  OF  OEGANS  IN  THE  FEOG. 

THE  unimpregnated  egg  has  a  certain  period  of  growth  within  the 
Graafian  follicle,  during  which  it  increases  in  size  from  the  insig- 
nificant dimensions  of  its  earlier  formation  to  those  of  its  maturity  as 
an  ovarian  egg.  The  vitellus,  at  first  transparent  and  colorless,  be- 
comes granular  and  opaque,  at  the  same  time  that  its  mass  is  enlarged 
by  the  deposit  of  new  elements;  and  in  birds  and  reptiles  it  also 
acquires  a  distinctive  hue,  generally  orange  or  yellow.  These  modifi- 
cations are  the  result  of  its  spontaneous  growth,  the  materials  for 
which  are  supplied  from  the  ovarian  tissues.  At  its  completion,  when 
the  egg  is  ready  to  be  discharged  from  the  ovary,  it  consists  of  the 
fully  formed  vitellus,  enclosed  in  a  vitelline  membrane,  and  containing, 
imbedded  in  its  substance,  the  germinative  vesicle  with  the  germina- 
tive  spot. 

Thus  constituted,  the  egg  leaves  the  ovary  on  the  rupture  of  the 
ovarian  follicle,  and  enters  the  Fallopian  tube.  Here,  if  coition  have 
taken  place,  it  meets  with  the  spermatozoa,  and  by  their  contact  and 
penetration  it  is  made  ready  for  the  production  of  the  embryo.  It 
is  consequently  transformed,  by  impregnation,  from  a  barren  offshoot 
of  the  ovarian  tissue  into  a  new  body,  in  wrhich  the  male  and  female 
elements  are  united,  and  which  possesses  a  capacity  for  further  de- 
velopment. 

Immediate  Effects  of  Impregnation. — The  first  change  in  the  egg, 
consequent  on  impregnation,  is  the  disappearance  of  the  germinative 
vesicle.  This  feature,  always  very  distinct  in  the  ovarian  egg,  becomes 
imperceptible  after  Its  contact  with  the  spermatic  fluid  in  the  Fallopian 
tube ;  and  its  place  is  subsequently  taken  by  a  new  formation,  which 
is  designated  as  the  "nucleus  of  the  impregnated  egg."  The  details 
of  this  substitution  have  not  been  fully  ascertained ;  but  its  important 
characters,  so  far  as  yet  known,  are  mainly  as  follows.*  The  germi- 
native vesicle  leaves  its  position  within  the  vitelline  mass  and  approxi- 
mates the  surface,  losing  at  the  same  time  a  portion  of  its  substance, 
becoming  smaller  in  size  and  elongated  in  form.  On  the  other  hand, 
a  spermatozoon,  which  has  penetrated  into  the  vitelline  sac,  becomes 
also  changed  by  the  disappearance  of  its  filamentous  portion;  and 


*  Kolliker,  Embryologie.     Paris,  1879,  p.  55. 

616 


DEVELOPMENT  OF  THE  IMPREGNATED  EGG.   617 

afterward  coming  in  contact  with  the  remainder  of  the  germinative 
vesicle,  the  two  unite  into  a  single  mass.  This  new  product,  made 
up  partly  of  the  germinative  vesicle  and  partly  of  the  spermatozoon, 
then  assumes  the  position  and  appearance  of  a  central  nucleus.  It  is 
regarded  as  the  point  of  origin  for  all  subsequent  changes  in  the  im- 
pregnated egg. 

Deposit  of  Albuminous  Layers  in  the  Fallopian  Tube. — As  the 
impregnated  egg  passes  down  the  Fallopian  tube,  it  becomes  covered 
with  an  albuminous  secretion.  In  birds,  this  secretion  is  deposited  in 
layers  round  the  vitellus,  forming  the  so-called  "white  of  egg."  In 
reptiles,  it  is  also  poured  out  in  considerable  quantity,  and  serves  for 
the  nourishment  of  the  egg  during  its  development.  In  mammalians, 
a  similar  secretion  is  supplied  in  smaller  quantity,  but  sufficiently 
abundant  in  proportion  to  the  size  of  the  egg  in  the  earlier  stages 
of  its  growth,  before  it  has  established  a  connection  with  the  lining 
membrane  of  the  uterus. 

Segmentation  of  the  Vitellus. — A  remarkable  change  now  takes  place 
in  the  impregnated  egg,  by  which  its  structure  is  definitely  altered. 
This  is  known  as  the  division,  or  "  segmentation  "  of  the  vitellus.  Its 
globular  mass  is  marked  by  a  circular  furrow,  which  gradually  deepens 
until  it  divides  the  vitellus  into  two  nearly  equal  halves  or  hemispheres. 
Each  hemisphere  is  then  found  to  contain  a  nucleus,  similar  to  that 
which  previously  occupied  the  centre  of  the  impregnated  vitellus  (Fig. 


SEGMENTATION  OF  THE  VITELLUS,  in  the  impregnated  egg  of  the  rabbit.    (Coste.) 

176,  A).  Almost  at  the  same  time  a  second  furrow,  at  right  angles 
with  the  first,  penetrates  the  vitellus  in  a  similar  way,  and  cuts  it  in  a 
transverse  direction.  The  vitellus  is  thus  divided  into  four  equal  por- 
tions, of  a  rounded  form,  lying  for  the  most  part  in  contact  with  each 
other  and  embraced  by  the  vitelline  membrane  (Fig.  176,  B).  The 


618  REPRODUCTION. 

space  existing  at  certain  points  between  them  and  the  vitelline  mem- 
brane is  occupied  by  a  transparent  fluid. 

The  process  thus  commenced  goes  on  by  the  repeated  formation  of 
furrows  in  various  directions,  dividing  the  four  separated  portions  suc- 
cessively into  eight,  sixteen,  thirty-two,  sixty-four,  and  so  on ;  until 
the  vitellns  is  converted  into  a  mulberry-shaped  collection  of  nearly 
spherical  nucleated  bodies,  resulting  from  its  continued  subdivision 
(Fig.  176,  C,  D).  These  bodies  are  termed  the  "vitelline  spheres." 
They  are  of  firmer  texture  than  the  original  vitellus ;  appearing  to 
increase  in  consistency  as  they  multiply  in  numbers  and  diminish  in  size. 
They  become  at  last  so  abundant  as  to  assume  by  mutual  compression 
tin-  polygonal  form  (Fig.  176,  E),  lying  in  close  contact  with  each  other 
immediately  beneath  the  vitelline  membrane,  and  surrounding  a  central 
space  filled  with  transparent  fluid.  They  are  thus  converted  into  a 
layer  of  cells,  enclosing  the  original  cavity  of  the  egg,  and  enveloped 
by  the  vitelline  membrane  (Fig.  176,  E). 

The  segmentation  of  the  vitellus  is  the  primary  act  in  the  develop- 
ment of  the  impregnated  egg,  and  the  sign  that  the  formation  of  an 
embryo  has  commenced.  It  takes  place  in  all  species  of  animals, 
although  varying  in  detail  according  to  the  special  constitution  of  the 
egg  and  its  accessory  parts.  In  all  mammalia,  as  well  as  in  many 
invertebrates,  where  the  vitellus  is  very  small,  and  where  the  body  of 
the  embryo  immediately  after  its  formation  is  supplied  with  nourish- 
ment from  without,  the  process  is  that  described  above.  In  birds,  in 
scaly  reptiles,  and  in  many  fish,  where  the  vitellus  is  large  and  contains 
additional  nutritive  matter,  segmentation  takes  place  only  in  a  thin 
layer  on  the  surface;  and,  beginning  at  one  spot,  extends  outward, 
advancing  more  rapidly  at  the  centre  of  the  segmenting  region  than  at 
its  periphery.  But  in  all  cases  segmentation  of  the  vitellus  is  the  first 
change  in  the  process  of  development,  and  has  always  the  same  result, 
namely,  to  divide  the  vitellus  into  a  great  number  of  minute  bodies, 
which  present  the  character  of  cells. 

Blastoderm,  or  Germinal  Membrane. — The  cells  formed,  in  the  man- 
ner above  described,  by  the  segmentation  of  the  vitellus,  become  more 
closely  packed  as  they  increase  in  number ;  and  finally,  by  mutual  con- 
tact and  adhesion  at  their  edges,  they  form  a  continuous  organized 
membrane,  kno\vii  as  the  germinal  membrane  or  blastoderm. 

Durinir  the  formation  of  this  membrane,  the  egg,  while  passing 
through  the  Fallopian  tube,  increases  in  size.  The  albuminous  matter 
with  which  it  is  enveloped  is  liquefied  and  absorbed  by  the  vitelline 
membrane,  I'lirnishinu'  material  for  the  growth  of  the  newlv-fonned 
structures.  A  certain  quantity  of  albuminous  fluid  also  accumulates 
in  the  central  cavity  of  the  eu'u-. 

The  next  change  consists  in  the  appearance  in  the  blastoderm  of  two 
separate  layers,  known  as  the  r.rfrrnal  and  internal  hloxlodermic  layers. 
They  are  both  still  composed  exclusively  of  cells;  but  those  of  the 
external  layer  are  -mailer  and  more  compact,  those  of  the  internal 


DEVELOPMENT  OF  THE  IMPREGNATED  EGG.   619 

larger  and  softer.  The  egg  then  has  the  form  of  a  globular  sac,  the 
walls  of  which  consist  of  three  concentric  layers,  in  contact  with  each 
other,  namely :  1st,  the  structureless  vitelline  membrane  inclosing  the 
whole ;  2d,  the  external  blastodermic  layer,  composed  of  cells ;  and  3d, 
the  internal  blastodermic  layer,  also  composed  of  cells.  The  cavity  of 
the  egg  is  occupied  by  an  albuminous  fluid,  absorbed  from  the  exterior 
and  destined  to  serve  as  nutritious  material. 

It  is  by  this  process  that  the  simple  globular  mass  of  the  vitellus  is 
converted  into  an  organized  structure.  For  the  blastoderm,  although 
consisting  of  cells  which  are  nearly  uniform  in  size  and  shape,  is  never- 
theless a  distinct  membrane,  made  up  of  anatomical  elements ;  and  its 
completion  marks  the  first  stage  in  the  formation  of  the  embryo.  The 
blastoderm  is  in  fact  the  embryo  in  its  primitive  condition ;  and  although 
its  texture  is  at  this  time  exceedingly  simple,  all  the  bodily  organs  are 
afterward  produced  by  the  modification  of  its  different  parts.  The 
further  process  of  formation  is  comparatively  simple  in  some  animals, 
more  complicated  in  others ;  and  its  general  features  are  most  easily 
understood  by  commencing  with  the  study  of  development  as  it  takes 
place  in  the  frog. 

Formation  of  Organs  in  the  Frog. — The  egg  of  the  frog,  when 
discharged  and  fecundated,  is  deposited  in  the  water,  enveloped  in  an 
albuminous  covering  of  gelatinous  consistency.  It  is  thus  exposed  to 
the  light,  the  air,  and  the  moderate  warmth  of  the  sun's  rays,  and  is 
supplied  with  abundance  of  moisture  and  nutritious  material.  Its 
development  is  distinguished  by  a  character  of  great  simplicity ;  since 
the  whole,  or  nearly  the  whole,  of  the  vitellus  is  directly  converted  into 
the  body  of  the  embryo.  There  are  no  accessory  organs,  and  conse- 
quently no  complications  of  the  formative  process. 

The  two  blastodermic  layers  above  described  represent  the  commence- 
ment of  the  new  organism.  They  serve,  however,  for  the  production 
of  different  parts ;  and  the  entire  process  of  development  may  be  con- 
cisely expressed  as  follows : 

I.  The  external  blastodermic  layer  produces  the  cerebro-spinal  axis 
and  the  epidermis  of  the  general  integument. 

II.  The  internal  blastodermic  layer  produces  the  epithelium  of  the 
alimentary  canal  and  adjacent  glandular  organs. 

III.  An  intermediate  layer,  which  subsequently  appears  between  the 
two,  produces  the  vascular  tissues,  and  thus  completes  the  constitution 
of  the  bodily  frame. 

The  first  sign  of  advancing  organization  in  the  blastoderm  shows 
itself  in  a  thickening  and  condensation  of  its  structure.  The  thickened 
portion  has  the  form  of  an  elongated  spot,  termed  the  "  embryonic 
spot"  (Fig.  1*77),  the  wide  edges  of  which  are  more  opaque  than  the 
adjacent  parts.  Between  these  opaque  edges  is  a  narrower,  colorless, 
and  transparent  space— the  "area  pellucida,"  within  which  is  a  delicate 
line,  running  longitudinally  from  front  to  rear,  called  the  "  primitive 
trace." 


620  REPRODUCTION. 

In  the  anterior  portion  of  the  area  pellucida,  the  substance  of  the 
blastoderm  rises  up  in  such  a  manner  as  to  form  two  nearly  parallel 
ridges  or  plates,  which  approach  each  other  from  side  to  side,  over  what 

will  be  the  dorsal  aspect  of  the  embryo, 

Fia- 1~~- and  are  therefore  called  the  "dorsal  plates." 

Between  them  is  included  a  groove, 
termed  the  "medullary  groove."  The 
dorsal  plates  afterward  meet  and  coalesce 
on  the  median  line,  thus  converting  the 
intervening  groove  into  a  canal.  The 
coalescence  of  the  dorsal  plates  takes 
place  first  in  the  anterior  part  of  the  area 
pellucida,  extending  thence  gradually  back- 
ward ;  and  when  it  is  complete  the  whole 

Diagrammatic  view  of  the  IMPREG-     °f    tllG  medullary  grOOVC    becomes  a  dosed 

NATED  EGO,  showing  the  embryonic    canal.     This   is   the    "  medullary  canal;" 

•pot,  area  pellucida,  and  primitive     ^  witMn  ^  {&  f()rmed    ^    ccrebro.spinal 

axis,   by   a    growth   of   nervous    matter 

from  its  internal  surface.  At  its  anterior  extremity,  the  medullary 
canal  is  large  and  rounded,  producing  the  brain  and  medulla  oblongata ; 
its  remainder  is  narrow,  and  pointed  posteriorly,  corresponding  in  form 
with  the  future  spinal  cord.  At  the  same  time,  the  thickened  edges  of 
the  blastoderm  grow  outward  and  downward,  extending  over  the  lateral 
portions  of  the  vitelline  mass.  They  are  called  the  "  abdominal  plates ;" 
and  they  approach  each  other  below  enclosing  the  abdominal  cavity,  as 
the  dorsal  plates  above  enclose  the  medullary  canal.  At  last  they  unite 
on  the  median  line,  embracing  the  whole  of  the  internal  blastodermic 
layer,  which  encloses  in  turn  the  remains  of  the  vitellus  and  the  albu- 
minous fluid  contained  in  its  cavity. 

Simultaneously  with  these  changes,  there  is  formed,  in  the  thickened 
central  part  of  the  blastoderm,  immediately  beneath  the  medullary 
canal,  a  longitudinal,  cylindrical  cord — the  "  chorda  dorsalis."  Around 
the  chorda  dorsalis  are  afterward  developed  the  bodies  of  the  vertebrae, 
the  oblique  processes  of  the  vertebra?  running  upward  into  the  dorsal 
plates,  while  the  transverse  processes  and  ribs  run  outward  and  down- 
ward in  the  abdominal  plates,  to  encircle  more  or  less  completely  the 
corresponding  portion  of  the  body. 

In  a  longitudinal  section  of  the  egg,  during  this  process,  the  thickened 
portion  of  the  external  blastodermic  layer  (Fig.  178,  ,)  may  be  seen  in 
profile.  The  anterior  portion  (,,),  which  will  form  the  head,  is  thicker 
than  the  posterior  (3),  which  will  form  the  tail.  As  the  whole  mass 
jrroNvs  rapidly,  in  both  the  anterior  and  posterior  direction,  the  head 
becomes  thick  and  voluminous,  while  the  tail  begins  to  project  back- 
ward, and  the  egg  assumes  an  elongated  form.  (Fig.  179.)  The  abdom- 
inal plates  also  meet  upon  its  under  surface,  and  complete  the  closure  of 
the  abdominal  cavity.  The  internal  blastodermic  layer  is  embraced  by 
the  abdominal  plates,  enclosing,  as  before,  the  remains  of  the  vitellus. 


DEVELOPMENT  OF  THE  IMPREGNATED  EGG.   621 

As  development  goes  on  (Fig.  180),  the  head  becomes  larger,  and 
shows  traces  of  the  organs  of  special  sense.     The  tail  also  increases  in 


FIG.  178. 


FIG.  179. 


FIG.  180. 


Diagram  of  FROG'S  EGG,  in  an  early  stage  of  de-  EGG  OF  FROG,  in  process  of  development, 
velopment ;  longitudinal  section.— 1.  Thickened 
portion  of  external  blastodermic  layer.  2.  An- 
terior extremity  of  the  embryo.  3.  Posterior 
extremity.  4.  Internal  blastodermic  layer.  5. 
Cavity  of  vitellus. 

size,  and  projects  farther  from  the  posterior  extremity  of  the  embryo. 
The  spinal  cord  runs  in  a  longitudinal  direction  from  front  to  rear,  and 
its  anterior  extremity  enlarges,  to  form  the  brain  and  medulla  oblon- 
gata.  In  the  mean  time,  the  internal  blastodermic  layer,  subsequently 

converted  into  the  epithelium  of  the 
intestinal  canal,  has  been  shut  in  by 
the  abdominal  walls,  and  forms  a  closed 
sac,  of  slightly  elongated  figure,  with- 
out inlet  or  outlet.  Afterward,  the 
mouth  is  formed  by  a  perforation 
through  both  external  and  internal 
layers  at  the  anterior  extremity ;  while 
a  similar  perforation,  at  the  posterior 
extremity,  results  in  the  formation  of  the  anus. 

By  a  continuation  of  the  same  process,  together  with  the  develop- 
ment of  the  intermediate  vascular  layer,  the  different  portions  of  the 
body  are  gradually  constructed,  producing  the  skeleton,  the  integument, 

FIG.  181. 


EGG  OF  FROG,  farther  advanced. 


TADPOLE,  fully  developed. 


the  organs  of  special  sense,  and  the  muscles  and  nerves.  The  tail  acquires 
sufficient  size  and  strength  to  be  capable  of  acting  as  an  organ  of  loco- 
motion (Fig.  181).  The  intestinal  canal  is  at  first  a  short,  wide,  nearly 


622  REPRODUCTION. 

straight  tube,  running  directly  from  the  mouth  to  the  anus.  It  then 
begins  to  grow  faster  than  the  abdominal  cavity  which  encloses  it, 
becoming  longer  and  narrower,  and  at  the  same  time  thrown  into 
numerous  curvilinear  folds. 

Arrived  at  this  period,  the  young  tadpole  ruptures  the  vitelline  mem- 
brane, and  leaves  the  cavity  of  the  egg.  He  at  first  attaches  himself  to 
the  remains  of  the  albuminous  envelope,  and  feeds  upon  it  for  a  short 
time.  He  soon,  however,  acquires  sufficient  strength  and  activity  to 
swim  about  in  search  of  other  food,  propelling  himself  by  his  large, 
membranous,  and  muscular  tail.  The  alimentary  canal  increases  in 
length  and  becomes  spirally  coiled  in  the  abdominal  cavity,  attaining 
a  length  from  seven  to  eight  times  greater  than  that  of  the  entire 
body. 

Afterward,  a  change  takes  place  in  the  external  form  of  the  animal. 
The  posterior  limbs  are  the  first  to  make  their  appearance,  by  budding 
or  sprouting  from  the  sides  of  the  body  at  the  base  of  the  tail.  The 
anterior  extremities  are  for  a  time  concealed  beneath  the  integument, 
but  afterward  become  liberated,  and  show  themselves  externally.  At 
first  both  the  fore  and  hind  legs  are  very  small,  incomplete  in  structure, 
and  useless  for  locomotion.  They  subsequently  increase  in  size  and 
strength ;  while  the  tail,  on  the  contrary,  ceases  to  grow,  and  becomes 
shrivelled  and  atrophied.  The  limbs,  in  fact,  are  destined  to  replace 
the  tail  as  organs  of  locomotion ;  and  a  time  at  last  arrives  when  the 
tail  has  altogether  disappeared  while  the  legs  are  fully  developed,  mus- 
cular, and  powerful.  Then  the  animal,  heretofore  confined  to  an  aquatic 
mode  of  life,  becomes  capable  of  living  on  land,  and  the  tadpole  is  trans- 
formed into  the  frog. 

During  the  same  time,  other  changes  take  place  in  the  internal  organs. 
The  tadpole  at  first  breathes  by  gills;  but  these  organs  subsequent!  v 
become  atrophied,  and  are  replaced  by  lungs.  The  structures  of  the 
mouth,  of  the  integument,  and  of  the  circulatory  system,  are  altered 
to  correspond  with  the  varying  conditions  of  the  growing  organism ; 
and  these  transformations,  taking  place  in  part  successively  and  in  part 
simultaneously,  bring  the  body  at  last  to  a  state  of  completion. 

The  development  of  a  young  animal  from  the  egg  consists  therefore 
of  a  series  of  changes,  in  which  different  organs  make  their  appearance 
from  modifications  of  the  blastoderm.  Many  of  these  organs  are  tem- 
porary, serving  for  the  growth  of  the  embryo  during  a  certain  period; 
while  others  are  of  more  permanent  structure,  and,  after  passing  through 
various  alterations  of  size  and  form,  become  component  parts  of  the 
adult  organism. 


CHAPTER  VII. 
FORMATION  OF    THE  EMBRYO  IN  THE  FOWL'S  EGG. 

fTlHE  process  of  embryonic  development  in  the  egg  of  the  bird  differs 
JL  from  that  of  the  frog  in  two  important  particulars.  First,  the 
whole  of  the  vitellus,  or  yolk,  in  the  bird's  egg,  is  not  directly  converted 
into  the  body  of  the  embryo,  but  a  large  part  is  transformed  into  a 
nutritious  fluid,  and  thus  serves  indirectly  for  its  growth.  Secondly, 
certain  accessory  organs  make  their  appearance,  extending  beyond  the 
limits  of  the  body  of  the  embryo,  and  surrounding  it  with  membranous 
envelopes.  The  development  of  the  chick,  during  incubation,  has  been 
found  especially  favorable  for  the  study  of  many  details  as  to  the 
formation  and  growth  of  the  various  organs ;  and  some  of  the  most 
valuable  discoveries  in  embryology  have  been  obtained  in  this  way. 

The  Yolk  and  the  Cicatricula. — The  yolk  of  the  fowl's  egg  represents 
something  more  than  the  vitellus  proper.  Its  principal  mass  consists 
of  an  opaque,  yellow,  semifluid  substance,  the  "  yellow  yolk,"  which 
solidifies  on  boiling,  owing  to  its  large  proportion  of  albuminous  matter. 
This  substance  contains  an  abundance  of  soft,  spherical,  finely  granular 
bodies,  from  25  to  100  mmm.  in  diameter. 

The  yellow  yolk  is  everywhere  surrounded  by  a  thin  nearly  colorless 
layer,  the  "  white  yolk,"  which  contains,  instead  of  the  granular  spheres 
above  described,  smaller  globular  bodies  with  one  or  more  brightly 
refracting  masses  in  their  interior.  The  albuminous  matter  of  the 
white  yolk,  furthermore,  does  not  solidify  firmly  on  the  application  of 
heat ;  so  that  in  a  boiled  egg  the  thin  stratum  of  this  substance  remains 
semifluid.  There  is  also  a  spot  at  the  centre  of  the  yolk,  which  is 
occupied  by  the  same  material,  and  which  consequently  remains  soft 
in  the  boiled  egg ;  the  cavity  thus  left  communicating  with  the  surface 
of  the  yolk  by  a  narrow  passage,  like  the  neck  of  a  flask. 

The  yolk  is  thus  formed  of  two  substances,  distinguished  by  their 
microscopic  characters  and  by  their  comparative  coagulability  at  the 
boiling  temperature.  Neither  of  these  substances  corresponds  with  the 
granular  vitellus  of  the  mammalian  egg ;  they  constitute  a  deposit  of 
nutritious  material,  destined  for  the  support  of  the  embryonic  tissues. 

At  one  point  on  the  surface  of  the  yolk,  in  the  unfecundated  egg,  is 
a  whitish  circular  spot,  about  three  millimetres  in  diameter,  immediately 
beneath  the  vitelline  membrane.  This  is  the  cicatricula.  It  is  a  thin 
layer,  of  minutely  granular  structure ;  its  granules  being  imbedded  in 
a  homogeneous  substance  by  which  they  are  agglutinated  into  a  disk- 
like  mass.  In  its  centre  is  the  germinative  vesicle,  distinctly  visible  by 

623 


624  REPRODUCTION. 

its  transparency  and  well  defined  outline,  and  marked,  in  the  ovarian 
egg,  by  a  germinative  spot.  According  to  Kollikcr,  the  germinative 
spot  disappears  before  the  mature  yolk  is  discharged  from  the  ovary  ; 
and  it  is  consequently  not  visible  in  the  egg  in  the  oviduct. 

The  cicatricula  is  the  only  part  of  the  fowl's  yolk  which  undergoes 
segmentation,  and  which  is  directly  concerned  in  the  production  of  the 
embryo.  It  corresponds  therefore  with  the  vitellus  of  the  mammalian 
egg,  and  has  ivcrm-d  the  name  of  the  "plastic"  or  formative  vitellus; 
while  the  remainder,  consisting  of  the  white  and  yellow  yolk,  is  known 
as  the  •'  nutritive"  vitellus.  The  position  of  the  cicatricula  is  imme- 
diately above  the  tubular  prolongation  of  white  yolk  leading  to  the 
central  cavity  of  the  egg. 

Segmentation  in  the  FowVs  Egg,  and  Formation  of  the  Blastoderm. 

The  fowl's  egg  is  fecundated  soon  after  leaving  the  ovary,  in  the 

upper  portion  of  the  oviduct.  Segmentation  begins  in  the  lower  half 
of  the  oviduct  and  goes  on  during  the  production  of  the  shell  mem- 
branes and  shell ;  and  in  the  new-laid  egg  the  formation  of  the  blasto- 
derm is  usually  complete. 

The  process  of  segmentation  in  the  fowl's  egg  differs  from  that 
already  described  (page  017)  in  the  following  particulars:  Instead  of 
a  globular  vitellus  successively  bisected  into  smaller  spheres  and  hemi- 
spheres, there  is  a  flattened  vitelline  disk,  the  cicatricula,  which  is  cut 
by  superficial  furrows,  running  in  various  directions,  and  dividing  its 
area  into  a  number  of  spaces  by  their  intersection.  The  principal  fur- 
rows radiate  from  the  central  part  of  the  cicatricula,  and  arc  united  at 
irregular  intervals  by  cross  furrows,  which  mark  off  isolated  portions 
of  its  substance.  The  cicatricula  is  thus  broken  up  into  a  large  number 
of  segments ;  but  this  segmentation  takes  place  by  extension  over  a  flat- 
tened surface,  spreading  gradually  from  the  centre  outward,  instead  of 
affecting  at  once  the  whole  vitellus,  as  in  the  mammalian  egg. 

The  details  of  segmentation  in  the  fowl's  egg  have  been  most  fully 
studied  by  Coste*  and  Kolliker.f  It  begins  by  the  appearance  of 
a  straight  or  curvilinear  furrow,  crossing  the  middle  portion  of  the 
cicatricula  without  reaching  to  its  edges,  and  dividing  it  imperfectly 
into  two  nearly  equal  halves  (Fig.  182,  I.).  This  furrow  is  afterward 
crossed  at  right  angles  by  a  second,  dividing  the  disk  into  four  sec- 
tors (Fig.  182,  II.).  The  point,  however,  at  which  the  sectors  meet 
is  not  usually  the  exact  centre  of  the  cicatricula,  but  a  little  on  one 
side ;  and  the  whole  process  of  segmentation,  according  to  Kolliker, 
goes  on  in  such  a  way  that  its  point  of  greatest  activity  is  always 
somewhat  eccentric  in  position.  The  primary  furrows  thus  formed  are 
followed  by  others  which  radiate  toward  the  edges  of  the  cicatricula, 
while  its  central  parts  are  broken  up,  as  above  described,  into  smaller 


:  Ilistnirr  (Ji'm'-rah-    rt    juirtirulu-iv   <lu    D6veloppement   des   Corps  organises. 

1S47  -:>'.).     1'o.ik-,  I'l.  ii.,  Figs.  7-13. 
f  Embryologie.     Paris,  1S71),  p.  63-85. 


FORMATION   OF   THE   EMBRYO   IN   THE   FOWL?S   EGG.    625 

segments  by  transverse  and  oblique  furrows  of  communication  (Fig. 
182,  III.).  By  the  continuance  and  peripheral  extension  of  this  process 
the  area  of  segmentation  is  gradually  divided  into  small  polygonal 
bodies  (Fig.  182,  IT.),  many  and  finally  all  of  which  are  provided  with 
a  central  nucleus,  and  which  are  accordingly  regarded  as  nucleated  cells. 
The  study  of  perpendicular  sections  of  the  cicatricula  in  this  condi- 


FIG.  182. 


PHASES  OF  SEGMENTATION  IN  THE  CICATRICULA  OF  THE  FOWL'S  EGG,  within  the  oviduct. 

(Kolliker.) 

tion  shows  that  its  segmentation  extends  not  only  in  a  lateral  direction, 
but  also  throughout  its  depth.  The  furrows  which  appear  to  divide  it 
into  isolated  parts  are  at  first  only  superficial,  and  its  surface  is  already 
subdivided  while  its  deeper  portions  are  still  entire.  But  the  process 
of  division  continues  from  above  downward  until  it  occupies  the  whole 
thickness  of  the  plastic  vitellus,  to  the  surface  of  the  white  yolk.  By 
this  means  the  cicatricula  is  converted  into  a  disk-like  mass  of  nucleated 
cells,  and  is  then  known  as  the  "blastoderm." 

2P 


626  REPRODUCTION. 

In  the  new-laid  egg,  the  blastoderm  is  already  composed  of  two 
layers.  The  external  layer,  at  this  time  the  more  completely  formed 
of  the  t\vo,  consists  in  its  central  portions  of  closely  packed  cylindrical 
cells,  in  several  superimposed  ranges ;  and  toward  its  outer  borders  of 
:i  single  range  of  flattened  cells,  placed  edge  to  edge.  The  internal 
layer  consists  of  rounded  cells,  more  coarsely  granular  than  those  of 
the  external  layer,  and  less  closely  consolidated  into  a  continuous  mass. 
This  is  the  condition  of  the  blastoderm  in  the  fecundated  fowl's  egg,  at 
the  time  of  its  discharge  from  the  generative  passage. 

Incubation  of  the  Egg  and  Formation  of  the  Embryo. 

When  the  fecundated  egg  is  discharged  from  the  generative  passage 
and  allowed  to  cool,  the  process  of  development  is  suspended  at  the 
point  above  described.  The  formative  changes  in  the  blastoderm 
require  for  their  accomplishment  a  warmth  nearly  equal  to  that  of  the 
fowl's  body,  namely,  about  40°  C. ;  and  the  egg,  if  kept  at  lower  tem- 
peratures, may  remain  inactive  for  a  considerable  time  without  losing 
its  vitality.  When  the  necessary  warmth  is  again  supplied,  by  natural 
or  artificial  incubation,  development  recommences  and  goes  on  to  the 
formation  of  the  embryonic  tissues. 

Extension  of  the  Blastoderm. — The  first  modification  in  the  egg  dur- 
ing incubation  is  the  increase  in  size  of  the  blastoderm.  This  mem- 
brane has  already  become  larger  than  the  cicatricula  from  which  it  was 
produced ;  for  while  the  average  diameter  of  the  cicatricula  before  seg- 
mentation is  about  three  millimetres,  the  blastoderm  in  the  new-laid 
egg  measures  from  three  and  a  half  to  four  millimetres  (Kolliker). 
But  when  incubation  commences,  it  expands  so  rapidly  that  in  twenty- 
four  hours  it  is  11  or  12  millimetres  in  diameter,  and  by  the  end  of  the 
second  day  it  reaches  twice  that  size.  By  the  continued  expansion  of 
its  borders  it  covers  more  and  more  of  the  spherical  yolk,  passing  after 
a  time  the  equatorial  line  and  approaching  its  opposite  pole.  At  tin- 
end  of  the  fourth  day  there  is  only  a  small  space  which  it  has  not  yet 
covered,  and  by  the  sixth  day  it  has  completely  enveloped  the  yolk  in 
a  sac-like,  membranous  extension.  The  nutritive  vitellus  is  thus  finally 
enclosed  by  the  expanding  blastoderm. 

Area  Pellucida  and  Primitive  Trace. — The  next  most  striking  feat- 
ure of  the  incubated  egg  is  the  appearance,  at  the  central  part  of  the 
blastoderm,  of  the  circular  spot,  known  as  the  "area  pellucida."  It  is 
so  called  from  its  transparent  appearance,  due  to  the  uniform  structure 
and  close  approximation  of  the  cells  of  the  external  blastodermic  layer 
in  this  situation.  The  area  pellucida  occupies  about  one-half  the  extent 
of  the  whole  blastoderm,  which  is  at  this  time  from  four  to  five  milli- 
metres in  diameter.  It  is  surrounded  by  the  remaining  non-transparent 
portion  of  the  blastoderm,  the  "area  opaca,"  the  opacity  of  which  is 
due  to  the  fact  that  its  internal  blastodermic  layer,  formed  of  lar-e. 
loosely  packed  and  rounded  cells,  is  two  or  three  times  as  thick  as  tin- 
external  layer.  In  the  area  pellucida,  on  the  contrary,  the  principal 


FORMATION   OF   THE   EMBRYO   IN   THE   FOWI/S   EGG.    627 

thickness  of  the  blastoderm  is  formed  by  the  external  layer ;  the  inter- 
nal consisting  of  only  a  single  range  of  cells,  often  incompletely  con- 
tinuous. As  the  blastoderm  enlarges,  its  area  pellucida  encroaches  on 
the  space  previously  occupied  by  the  area  opaca ;  and  the  area  opaca 
expands  in  turn,  advancing  beyond  the  borders  of  the  transparent  por- 
tion. The  area  pellucida  soon  assumes  an  oval  form,  placed  trans- 
versely to  the  long  axis  of  the  egg ;  and  the  body  of  the  embryo  will 
afterward  occupy  the  same  position,  the  wider  end  of  the  oval  corre- 
sponding to  the  future  situation  of  the  head,  its  narrower  end  to  that 
of  the  tail. 

"Not  long  after  the  formation  of  the  area  pellucida,  it  presents  in  its 
longitudinal  axis  a  slight  linear  eminence,  caused  by  local  thickening 
and  condensation  of  the  external  blastodermic  layer.  This  is  known 
as  the  "  primitive  trace."  It  appears,  from  the  tenth  to  the  fourteenth 
hour  of  incubation,  as  an  ill-defined  linear  opacity,  about  one  milli- 
metre in  length  and  0.2  millimetre  in  width,  of  a  straight  or  slightly 
sinuous  form,  and  somewhat  eccentric  in  position,  occupying  rather 
the  posterior  than  the  anterior  portion  of  the  area  pellucida  It  shows, 
along  the  median  line  on  its  upper  surface,  a  shallow  depression,  the 
" primitive  furrow,"  and  by  the  fifteenth  hour  of  incubation  it  is  fully 
constituted  in  all  its  parts. 

The  primitive  trace,  although  it  indicates  the  direction  of  the  longi- 
tudinal axis  of  the  future  embryo,  is  not  an  initial  formation  of  the 
embryonic  organs,  and  takes  no  direct  part  in  their  development.  It 
is  a  transitory  structure,  which  disappears  soon  after  its  production, 
and  gives  place  to  others  of  more  permanent  significance.  But  it  is  a 
feature  of  much  interest,  as  the  earliest  local  modification  in  the  trans- 
parent portion  of  the  blastoderm. 

Formation  of  Three  Blastodermic  Layers. — The  blastoderm,  at  the 
time  of  its  appearance  in  the  new-laid  egg,  consists,  as  above  described, 
of  two  layers  of  cells,  namely,  an  external  and  an  internal.  Of  these, 
the  external  alone  is  fully  constituted ;  the  internal  being  less  complete 
and  more  or  less  discontinuous  in  the  central  portions  of  the  blastoderm. 
But  a  few  hours  after  the  commencement  of  incubation,  the  internal 
blastodermic  layer  becomes  continuous  throughout,  forming  everywhere 
a  distinct  consistent  expansion.  Within  the  limits  of  the  area  pellucida 
its  cells  assume  a  flattened  form,  being  thus  still  further  distinguished 
from  those  of  the  external  layer,  which  in  this  situation  are  more 
cylindrical  in  figure  and  multiply  with  great  rapidity.  Soon  after- 
ward a  third  blastodermic  layer  makes  its  appearance,  between  the 
other  two,  composed  of  uniformly  rounded  cells.  It  is  first  produced 
along  the  line  of  the  primitive  trace,  and  thence  extends  laterally  on 
each  side,  diminishing  in  thickness  until  it  terminates,  at  some  distance 
from  the  median  line,  in  a  thin  edge.  In  the  region  of  the  primitive 
trace  (Fig.  183)  the  blastoderm  is  then  composed  of  three  cellular 
layers,  which  have  received  distinct  names,  and  which  afterward  give 
origin  to  all  the  organs  of  the  embryo,  namely :  1st,  the  external  bias- 


828  REPRODUCTION. 

todermic  layer,  or  Ectoderm,  which  produces  the  cerebro-spinal  axis 
and  the  tegumcntary  epidermis;  2d,  the  internal  layer,  or  Entoderm, 
producing  the  intestinal  and  glandular  epithelium ;  and  3d,  the  inter- 

FIG.  183. 


Ml 

TRANSVERSE  SECTION  OP  BLASTODERM  OF  FOWL'S  EGG,  at  the  situation  of  the  primitive  trace 
and  primitive  furrow.    Ect,  Ectoderm.    Md,  Mesoderm.    Ent,  Entoderm.    (Kolliker.) 

mediate  layer,  or  Mesoderm,  from  which  the  great  mass  of  the  mus- 
cular system,  the  blood  and  circulatory  apparatus,  and  the  vascular 
tissues  in  general  are  subsequently  developed. 

Folds  of  the  Blastoderm. — The  form  of  the  embryo  and  its  different 
parts  is  sketched  out,  in  all  cases,  by  a  series  of  folds,  which  show 
themselves  at  various  points  in  the  blastoderm.  This  membrane  pre- 
sents at  first  a  flat  surface  ;  or,  if  it  have  a  certain  degree  of  convexity, 
corresponding  with  that  of  the  yolk  upon  which  it  lies,  this  convexity 
is  perfectly  uniform,  and  too  slightly  pronounced  to  be  appreciable 
within  the  limits  of  the  blastoderm.  But  as  soon  as  development 
begins  to  make  definite  progress,  this  uniformity  of  surface  is  broken 
by  the  appearance  of  transverse  and  longitudinal  folds,  forming  lines 
of  separation  between  different  parts  of  the  blastoderm.  Such  a  fold, 
running  in  a  curvilinear  direction  from  side  to  side,  marks  the  position 
of  the  head  of  the  embryo,  and  is  called  the  "  head-fold."  Its  free 
border,  projecting  above  the  neighboring  portion  of  the  blastoderm, 
becomes  the  head,  which,  as  well  as  the  neck,  is  curved  forward  and 
downward,  in  the  subsequent  stages  of  growth,  with  the  deepening  of 
the  fold  which  first  gave  it  origin  as  a  distinct  part.  A  similar  foM  at 
the  posterior  portion  of  the  area  pellucida,  marks  off  the  hinder  ex- 
tremity of  the  embryo,  and  is  called  the  "tail-fold."  Longitudinal 
folds,  formed  in  the  same  manner  on  each  side,  fix  the  lateral  limits  of 
the  body  of  the  embryo. 

By  this  means  a  certain  portion  of  the  blastoderm  becomes  marked 
off  from  the  rest.  The  part  included  within  the  transverse  and  longi- 
tudinal folds  is  the  body  of  the  embryo;  while  that  remaining  outside 
these  limits  becomes  developed  into  accessory  organs,  playing  nn  im- 
portant but  secondary  part  in  the  history  of  development.  Similar 
folds  of  the  blastoderm  also  make  their  appearance  within  the  body 
of  the  embryo,  and  are  the  principal  means  of  formation  for  its  differ- 
ent organs.  A  pair  ofloiigitudinal  ridges,  adjacent  to  the  median  line, 


FORMATION   OF  THE  EMBRYO   IN  THE   FOWI/S   EGG.    629 

form  the  two  halves  of  the  cerebro-spinal  axis,  which  afterward  coalesce 
with  each  other  along  their  dorsal  edges;  and  the  formation  of  the 
intestinal  canal,  as  well  as  its  inclosure  by  the  abdominal  walls,  results 
from  the  growth  of  lateral  folds  which  curve  downward  and  inward, 
to  meet  on  the  median  line  below.  Thus  the  body  of  the  embryo, 
consisting  mainly  of  the  thickened  ectoderm  and  mesoderrn,  is  at  first 
spread  out,  in  a  nearly  uniform  plane,  over  the  surface  of  the  yolk, 
resting  upon  the  entoderm,  which  represents  the  epithelial  lining  of 
its  future  alimentary  canal.  But  as  the  depressed  folds  of  its  lateral 
borders  penetrate  more  deeply  below  the  general  level,  the  sides  of 
the  embryo  shut  in  between  them  a  cavity,  which  is  afterward  com- 
pleted by  the  union  of  its  edges,  and  thus  finally  embraces  tne  ali- 
mentary canal,  with  the  other  thoracic  and  abdominal  organs. 

The  above  changes,  which  thus  determine  the  configuration  of  the 
embryo,  result  from  the  special  activity  of  growth  in  particular  parts 
of  the  blastoderm.  If  this  membrane  were  to  grow  only  at  its  edges, 
it  would  simply  extend  farther  over  the  vitellus,  its  central  portions 
remaining  as  before.  If  it  were  to  increase  everywhere  at  a  uniform 
rate,  it  would  become  thicker  as  well  as  more  extensive,  but  without 
any  special  alteration  of  form.  This  is  what  really  takes  place  during 
the  early  production  of  the  blastoderm,  which  at  first  expands  on  all 
sides,  retaining  its  original  uniformity  of  surface. 

But  with  the  commencement  of  incubation  the  blastoderm  grows 
more  rapidly  at  particular  points,  and  along  certain  lines,  than  else- 
where. What  may  be  the  determining  cause  of  such  a  concentration 
of  growth,  it  is  impossible  to  say ;  but  its  result  is  that  the  blastoderm, 
enlarging  with  different  degrees  of  rapidity  in  different  regions,  is 
thrown  into  undulations,  which  indicate,  by  their  position  and  size, 
the  unequal  expansion  of  its  mass.  Thus,  if  it  grow  more  rapidly  at 
one  point  than  in  the  adjacent  parts,  it  will  form  at  that  spot  either  an 
eminence  or  a  depression,  according  as  it  meets  with  less  resistance 
above  or  below.  If  a  similar  rapidity  of  increase  should  take  place 
along  a  transverse  line,  the  consequence  would  be  a  transverse  fold ; 
and  if  in  an  antero-posterior  direction,  it  would  cause  a  longitudinal 
fold.  The  subsequent  history  of  embryonic  development  shows  con- 
tinual repetitions  of  this  process,  often  on  a  much  larger  scale  than 
in  the  blastoderm.  The  folds  of  the  intestinal  canal,  the  valvulae  con- 
niventes  of  its  mucous  membrane,  the  convolutions  of  the  brain,  and 
the  tubular  windings  of  the  perspiratory  glands,  with  many  other 
analogous  forms,  are  produced  in  a  similar  way.  All  these  structures 
are  at  first  smooth  or  straight.  They  become  thrown  into  folds  or 
convolutions  during  the  development  of  the  embryo,  whenever  they 
grow  more  rapidly  than  the  surrounding  parts. 

Position  of  the  Embryo  in  the  Egg. — Although  the  blastoderm  is  at 
first  apparently  of  uniform  structure  throughout,  yet  each  particular 
part  has  from  the  beginning  a  physiological  individuality,  which  leads 
to  its  subsequent  development  into  a  special  organ  or  part  of  an  organ- 


630  REPRODUCTION. 

This  is  evident  from  the  manner  in  which  the  local  activity  of  nutrition 
irives  rise  to  the  appearance  of  folds,  running  in  definite  directions, 
and  determining  in  this  way  the  future  location  of  the  head,  the  tail, 
and  the  sides  of  the  body.  But  it  is  manifested  still  more  remarkably 
in  the  position  of  the  entire  embryo.  The  yolk  of  the  fowl's  egg  has 
a  nearly  regular  spherical  form  ;  and  the  cicatricula,  as  well  as  the  blas- 
toderm into  which  it  is  converted,  is  a  circular  spot  upon  its  surface. 
The  ovoid  form  presented  by  the  whole  egg,  with  one  round  and  one 
pointed  extremity,  results  from  the  deposit  of  albumen  around  the  yolk, 
in  the  middle  and  lower  parts  of  the  oviduct,  after  fecundation  has 
taken  place.  But  when  the  rudimentary  embryo  first  becomes  per- 
ceptible in  the  area  pellucida,  it  is  so  placed  in  the  large  majority  of 
instances  as  to  lie  crosswise  to  the  long  axis  of  the  egg,  with  its  left 
side  toward  the  round  end  and  its  right  side  toward  the  pointed  end. 
Even  before  incubation  has  commenced,  one  particular  portion  of  the 


TRANSVERSE  SECTION  OF  EMBRYO  CHICK,  second  day  of  incubation,  through  open  portion  of  me- 
dullary groove.— Mg.  Medullary  groove.  Dp.  Dorsal  plates.  Ch.  Chorda  dorsalis.  Ect.  Ectoderm. 
Md.  Mesoderm.  Ent.  Entoderm.  Magnified  83  times.  (Kolliker.) 

circular  blastoderm  is  destined  to  become  the  head  and  another  portion 
the  tail ;  and  consequently  every  one  of  the  future  organs  of  the  embryo 
has  its  point  of  origin  already  fixed. 

Dorsal  Plates,  Medullary  Canal,  and  Cerebro- Spinal  Axis. During 

th<>  first  day  of  incubation  the  primitive  trace  is  bordered  on  each  side 
and  around  its  two  extremities  by  a  thickened  extension  of  the  blasto- 
derm, whirh  rapidly  assumes  an  elongated  form  and  grows  more  rapidly 
in  the  anterior  than  in  the  posterior  direction.  Early  in  the  second 
day  there  appear,  within  the  embryonic  spot,  in  front  of  the  primitive 
trace,  two  parallel  longitudinal  folds  of  the  ectoderm,  which  project 
above  the  suriacr,  Ira  vino  between  them,  along  the  median  line,  a  cor- 
responding Ion-it  udinal  depression  (Fig.  184).  These  ectodermic  folds 
suv  known  as  the  "  dorsal  phites,"  :md  the  depression  between  them  is 
the  "  medullary  groove."  As  the  dorsal  plates  increase  in  height,  their 
edges  curve  inward,  and  the  interveninc;  groove,  which  is  lined  with 
the  cells  of  the  ectoderm,  becomes  deeper  and  more  capacious.  B\  a 
continuance  of  thi-  process,  the  ed-es  of  the  dorsiil  plates  are  more 


FORMATION   OF   THE   EMBRYO   IN   THE   FOWI/S   EGG.    631 

closely  approximated,  and  the  medullary  groove,  at  first  widely  open 
along  the  dorsal  surface,  is  reduced  at  its  opening  to  a  comparatively 
narrow  fissure  (Fig.  185). 

FIG.  185. 


Ect 


TRANSVERSE  SECTION  OF  EMBRYO  CHICK,  through  narrowed  portion  of  medullary  groove. — Mg. 
Medullary  groove.  Dp.  Dorsal  plates.  Ect.  Ectoderm.  Md.  Mesoderm.  Ent.  Entoderm.  Ch. 
Chorda  dorsalis.  p.  Peritoneal  space,  a  o.  Embryonic  aorta,  one  on  each  side.  (Kolliker.) 

That  the  dorsal  plates  are  formed,  in  the  manner  above  described, 
by  folds  of  the  ectoderm,  is  plain  from  the  fact  that  at  this  time  the 
layer  of  ectodermic  cells  lining  the  medullary  groove  is  reflected  con- 
tinuously on  each  side,  at  the  edges  of  the  dorsal  plates,  upon  the  adja- 
cent free  surface  of  the  blastoderm.  Finally,  the  dorsal  plates  come  in 
contact  at  their  edges  and  coalesce  with  each  other,  thus  obliterating 
the  fissure  between  them,  and  converting  the  medullary  groove  into  a 
closed  canal  (Fig.  186).  When  this  change  is  accomplished,  the  ecto- 
derm, which  was  originally  continuous  throughout,  is  divided  into  two 
portions — a  thicker  portion  lining  the  cavity  of  the  canal,  and  a  thin- 


TRANSVERSE  SECTION  OF  EMBRYO  CHICK,  through  closed  portion  of  medullary  canal.— Me.  Medul- 
lary canal.  Ect.  Ectoderm.  Ent.  Entoderm.  Md.  Md.  Outer  and  inner  laminae  of  Mesoderm.  p. 
Peritoneal  space,  ch.  Chorda  dorsalis.  a  o.  Aorta. 

ner  portion  covering  the  canal  along  the  median  line  and  thence  ex- 
tending laterally  over  the  general  surface  of  the  blastoderm.  The  canal 
thus  formed  is  the  "  medullary  canal."  The  layer  of  cells  by  which 
it  is  surrounded  afterward  produces  the  brain  and  spinal  cord,  or  the 


632 


REPRODUCTION. 


ccrebro-spinal  axis ;  and  the  canal  itself  becomes,  in  the  adult,  the  cen- 
tral canal  of  the  spinal  cord,  with  its  continuations  in  the  encephalon, 
namely,  the  fourth  ventricle,  aqueduct  of  Sylvius,  and  third  ventricle. 
The  external  portion  of  the  ectoderm,  remaining  outside  the  medullary 
canal  and  covering  the  surface  of  the  embryo,  becomes  the  epidermic 
layer  of  the  general  integument. 

The  coalescence  of  the  dorsal  plates,  by  which  the  medullary  groove 
is  converted  into  a  canal,  does  not  take  place  at  the  same  time  through- 
out.     It   is   first   completed  in   the 
Fl(;-  187-  middle   portion  of  what  will   after- 

ward be  the  head ;  the  anterior  part 
of  the  encephalon,  and  the  cervical 
and  dorsal  portions,  remaining  open 
until  a  later  period.  Their  final  clos- 
ure proceeds  in  a  general  direction 
from  before  backward,  occupying 
successive  portions  as  development 
goes  on,  and  reaching  at  last  the  pos- 
terior extremity. 

The  dorsal  plates,  as  the  imme- 
diate precursors  of  the  cerebro-spinal 
axis,  are  the  first  distinct  indication 
of  a  permanent  embryonic  organ. 
Their  relation  to  the  primitive  trace 
is  not  very  well  defined,  and  it  is 
doubtful  whether  they  are  especially 
connected  with  its  formation.  They 
first  appear  in  advance  of  its  anterior 
extremity  ;  and,  although  the  medul- 
lary groove  between  them  corre- 

EMBRYO^F  THE  CHICK,  at  th.  sP°nds   in   its   general    longitudinal 
thirtieth  hour  of  in. -ninition.    r<<.  Pro'to-  direction  with  the  median  furrow  of 

vertebrae.    Dp.  Dorsal  iilaii-s.  .)/,/.  Medullary    ,1  •      •  ,• 

groove.  P,-.  i>ri,Mi.iv,:, 1;,,,.   /Kniiikor.,  "   thc  primitive  trace,  the  two  are  not 

uniformly  continuous,  but,  according 

to  Kolliker,*  are  often  laterally  displaced,  the  one  falling  a  little  to  the 
ri.irht,  the  other  to  the  left.  The  medullary  groove  is  moreover  consid- 
erably \vidcr  than  the  primitive  furrow ;  and,  while  the  cephalic  region 
of  the  embryo,  as  well  as  its  cervical  and  dorsal  portions,  grow  very 
rapidly  with  the  progress  of  incubation,  the  primitive  trace  remains 
confined  to  the  caudal  extremity.  Its  greatest  length,  about  the  thir- 
tieth hour  of  incubation,  is  rather  less  than  two  millimetres  ;  it  begins 
to  diminish  perceptibly  from  the  fortieth  to  the  forty-second  hour,  and 
at  the  end  of  the  sennid  day  has  almost  disappeared.  By  this  time 
the  medullary  canal  is  eio>ed  for  nearly  the  whole  length  of  the  cere- 
bro-spinal  a\i>. 


l»ryologie.     Paris,  1879,  pp.  109,  141. 


FORMATION  OF  THE   EMBRYO   IN  THE   FOWI/S   EGG.    633 

Protovertebrae,  Chorda  Dorsalis,  and  Vertebral  Column. On  the 

first  appearance  of  the  dorsal  plates  and  medullary  groove,  at  the  be- 
ginning of  the  second  day  of  incubation,  these  structures  occupy  the 
anterior  half  of  the  rudimentary  embryo,  or  that  portion  which  will 
afterward  become  the  head.  Immediately  behind  this  region,  and 
slightly  in  front  of  the  primitive  trace,  a  transverse  division  becomes 
apparent  on  each  side  at  a  little  distance  from  the  median  line.  This 
division,  though  visible  externally  as  a  transparent  line,  is  really  situ- 
ated in  the  mesoderm,  the  cells  of  which  undergo  disintegration  at  this 
point  along  a  transverse  plane,  thus  causing  a  separation  between  its 
anterior  and  posterior  portions.  A  second  line  of  division  soon  follows, 
parallel  to  the  first  and  about  0.75  millimetre  behind  it,  including  be- 
tween the  two  a  nearly  rectangular  mass  of  the  body  of  the  embryo. 
Almost  immediately  a  third  line  appears  in  advance  of  the  first ;  and 
by  this  means  there  are  formed  on  each  side  two  well-defined  quad- 
rangular sections  of  the  mesoderm.  (Fig.  1ST.)  They  are  the  precur- 
sors of  a  longitudinal  chain  of  similar  divisions,  appearing  successively 
from  before  backward,  until  in  the  fourth  day  of  incubation  they  form 
a  series  of  twenty-one  or  twenty-two  pairs.  From  their  early  appear- 
ance and  their  resemblance  to  the  articulations  of  the  future  vertebral 
column,  they  have  received  the  name  of  the  "proto  vertebra." 

The  protovertebrse  first  formed  correspond  in  situation  with  the  ante- 
rior cervical  region  of  the  embryo.  The  second  pair,  in  the  order  of 
formation,  is  placed  in  advance  of  the  first ;  while  the  third  pair  appears 
immediately  behind  it.  (Fig.  188.)  At  this  time  the  closure  of  the  dorsal 
plates  has  taken  place  throughout  the  middle  portion  of  the  head,  while 
in  the  anterior  and  posterior  cephalic  regions  the  medullary  groove  is 
still  open.  In  the  cervical  region,  where  the  proto vertebrae  are  being 
formed,  this  groove  has  but  little  depth;  and  farther  back,  near  the 
situation  of  the  primitive  trace,  it  is  wider  and  shallower  still.  As 
additional  protovertebrae  become  visible  at  the  end  of  the  series,  those 
of  latest  formation  are  always  at  the  same  distance  in  front  of  the  prim- 
itive trace.  This  shows  that  they  are  formed  from  new  material  sup- 
plied by  a  rapid  growth  of  the  blastoderm  in  this  situation ;  each  pro- 
tovertebra  taking  the  place  of  that  which  preceded  it  in  the  order  of 
formation,  but  falling  behind  in  the  linear  series.  In  an  embryo  show- 
ing seven  or  eight  pairs  of  protovertebrae,  as  in  Fig.  189,  the  last  pair 
is  still  considerably  in  advance  of  the  caudal  extremity ;  and  the  re- 
maining pairs,  belonging  to  the  dorsal  region,  are  still  to  be  formed  by 
the  same  process.  At  this  time  the  medullary  canal  is  closed  through- 
out its  cephalic  portion,  but  is  still  open  in  the  cervical  region  at  the 
level  of  the  third  pair  of  protovertebrae.  From  this  point  backward  it 
becomes  gradually  shallower  and  wider,  expanding  to  its  greatest  width 
in  the  caudal  region,  where  it  embraces  the  anterior  extremity  of  the 
primitive  trace.  When  the  protovertebrae  have  reached  their  full  num- 
ber, at  the  forty-eighth  or  fiftieth  hour  of  incubation,  the  caudal  portion 


634 


REPRODUCTION. 


of  the  medullary  groove  still  extends  a  certain  distance  beyond  them, 
and  they  are  also  absent  from  the  region  of  the  head. 

The  subsequent  history  of  the  protovertebrae  consists  in  their  trans- 
formation into  other  tissues  and  their  final  disappearance  as  distinct 
organs.  Their  upper  and  outer  portions  are  mainly  converted  into  the 
voluntary  muscles  covering  the  spinal  column,  while  their  inferior  and 
inner  portions  supply  the  material  for  the  bodies  of  the  vertebrae,  the 
vertebral  arches,  and  the  intervertebral  ligaments.  During  this  process 


Fio.  188. 


fir 


RUDIMENTARY  EMBRYO 
OF  THE  CHICK,  at  the 
thirty-sixth  hour  of  in- 
cubation. Dp.  Dorsal 
plates,  cephalic  region. 
Mg.  Medullary  groove. 
Pv.  Anterior  pair  of 
proto vertebrae.  ( K«".l- 
liker.) 


EMBRYO  op  CHICK,  about  the  fortieth  hour  of  in- 
cubation. Ce.  Cephalic  extremity.  Pv.  Troto- 
vertebrse.  Dp.  Dorsal  plates,  still  widely  sep- 
arated in  the  caudal  region.  Pr.  Primitive 
trace.  (Kolliker.) 


they  become,  for  the  most  part,  fused  with  each  other  in  the  longitu- 
dinal direction,  and  by  the  end  of  the  fifth  day  the  divisions  between 
them  are  no  longer  visible. 

The  chorda  dorsalis,  already  mentioned  (page  620),  is  a  slender 
longitudinal  cylinder,  rather  less  than  0.1  millimetre  in  diameter,  situ- 
ated in  the  median  line,  between  the  ectoderm  and  entoderm,  imme- 
diately beneath  the  medullary  canal.  It  first  appears,  from  the  twentieth 
to  the  t \vcnty-f«Mirth  hour  of  incubation,  at  the  posterior  part  of  the 
medullary  groove.  It  thence  extends  forward,  during  the  second  day, 
to  a  point  corresponding  with  the  middle  region  of  the  head.  It  is 


FORMATION   OF   THE   EMBRYO   IN   THE    FOWI/S   EGG.    635 

composed  of  uniformly  rounded  cells  agglutinated  with  each  other,  as 
shown  in  Figs.  184,  185,  186. 

During  the  third  day  the  inner  and  lower  portions  of  the  protover- 
tebra?  extend  toward  the  median  line  in  such  a  manner  as  to  surround 
the  chorda  dorsalis,  above,  below,  and  on  each  side,  with  an  investment 
of  new  material.  As  these  newly  formed  portions  of  the  protovertebrae 
coalesce  with  each  other,  the  chorda  dorsalis  becomes  covered  with  a 
continuous  tubular  sheath,  or  investing  membrane.  This  forms  a  rudi- 
mentary vertebral  column ;  since  the  substance  of  the  sheath,  in  the 
further  progress  of  growth,  becomes  first  cartilaginous  and  afterward 
bony,  producing  finally  the  bodies  of  the  vertebra?. 

While  the  sheath  of  the  chorda  dorsalis  is  thus  formed  from  the 
inner  and  lower  portions  of  the  protovertebrae,  their  inner  and  upper 
portions  extend,  as  a  thin  expansion  on  each  side,  between  the  medul- 
lary canal  and  the  tegumentary  layer  of  the  ectoderm.  On  the  fourth 
day  these  lateral  growths  meet  and  coalesce  at  the  median  line,  on  the 
dorsal  aspect  of  the  embryo;  and  the  embryonic  spinal  cord  is  then 
enclosed  in  a  membranous  investment,  similar  to  that  of  the  chorda 
dorsalis.  In  this  investment  there  are  afterward  formed  the  oblique 
processes  of  the  vertebrae,  which,  by  uniting  with  each  other  in  the 
same  way  on  the  median  line,  finally  enclose  the  cerebro-spinal  axis  in 
a  series  of  vertebral  arches.  The  deposit  of  cartilaginous  matter,  in  the 
double  membranous  tube  thus  formed,  takes  place  at  successive  points 
in  a  linear  series ;  and  from  each  point  the  cartilaginous  deposit,  as 
well  as  its  subsequent  ossification,  extends  gradually  to  its  final  limit. 
The  intervening  portions,  not  converted  into  cartilaginous  and  bony 
tissues,  become,  between  the  bodies  of  the  vertebrae,  the  intervertebral 
ligaments,  and  between  the  dorsal  arches  the  yellow  ligaments  of  the 
vertebrae. 

But  in  this  transformation  of  a  portion  of  the  protovertebrae  into 
a  permanent  spinal  column,  the  final  arrangement  of  the  parts  is  differ- 
ent from  that  at  the  beginning.  When  the  cartilages  of  the  permanent 
vertebrae  make  their  appearance,  they  do  not  correspond  in  situation 
with  the  original  protovertebrse.  Subsequently  to  the  fusion  of  the 
protovertebraB  with  each  other,  a  new  segmentation  takes  place,  the 
lines  of  division  passing  through  the  former  intervening  spaces.  Each 
permanent  vertebra  therefore  corresponds  in  position  with  the  adjacent 
halves  of  two  protovertebra? ;  and  the  middle  portion  of  each  protover- 
tebra  is  finally  replaced  by  an  intervertebral  ligament. 

Area  Vasculosa,  Blood  and  Blood-vessels. — The  mesoderm,  during 
the  earliest  periods  of  incubation,  is  less  rapid  in  its  lateral  extension 
than  the  two  other  blastodermic  layers ;  but  it  undergoes  important 
changes  in  texture,  which  lead  to  the  development  of  the  vascular  sys- 
tem. This  begins  in  the  second  day.  Within  the  body  of  the  embryo 
at  this  time  the  mesoderm  exhibits  on  each  side,  at  some  distance 
from  the  median  line,  a  horizontal  cleft  (Fig.  185,  p),  by  which  it  is 
divided  into  two  laminae,  one  above,  contiguous  to  the  ectoderm,  and 


636 


REPRODUCTION. 


one  below,  next  the  entoderm  ;  and  a  little  later  (Fig.  186)  the  division 
IK  'tween  them  is  more  complete.  This  cleft  represents  the  future  peri- 
toneal cavity.  The  external  lamina  of  the  mesoderm  will  afterward 
supply  the  voluntary  muscles  and  other  tissues  of  the  thoracic  and 
abdominal  walls;  while  the  involuntary  muscular  layer  of  the  aliment- 
ary canal  is  derived  from  its  internal  lamina.  Outside  the  body  of 
the  embryo  the  internal  lamina  increases  in  thickness,  and  becomes  of 
great  importance  in  the  formation  of  the  blood  and  blood-vessels. 

The  first  appearance  of  vascularity  shows  itself,  early  in  the  second 
day,  in  the  parts  immediately  surrounding  the  area  pellucida.     Certain 

FIG.  190. 


PORTION  OF  THE  VASCULAR  AREA,  from  the  blastoderm  of  the  chick  at  the  fortieth  hour  of  incu- 
bation, showing  islets  of  blood  ami  rml>ry<inir  I >lood- vessels.     Vt.  Vena  tcrminalis.    (Kolliker.) 

spots  in  the  mesoderm  of  this  region  assume  the  form  of  irregularly- 
shaped  spaces  filled  with  red  blood  globules,  which  soon  unite  with  each 
other  in  such  a  way  as  to  form  a  network  of  inosculating  vessels.  The 
region  of  the  blastoderm  occupied  by  this  network  is  known  as  the 
"  area  vasculosa."  There  is  at  first  no  arrangement  of  the  blood-vessels 
in  trunks  and  branches,  nor  any  apparent  distinction  corresponding  to 
that  of  arteries  and  veins.  All  are  of  nearly  the  same  size,  distributed 
on  the  same  plane  and  communicating  equally  with  each  other;  except 
that  they  are  surrounded  by  a  large  vessel,  the  "vena  tenninalis,11  with 
which  all  the  adjacent  vessels  communicate  and  which  thus  forms  the 
exterior  limit  of  the  vascular  area  (Fig.  190).  Subsequently  a  differ- 
ence shows  itself  in  the  extent  and  rapidity  of  their  growth,  some  pre- 
ponderating in  size  over  the  others ;  and  by  the  end  of  the  third  day 
there  is  a  visible  distinction  between  their  trunks,  branches,  and  rami- 
fications. At  the  same  time  the  formation  of  blood-vessels  extends 


FOKMATION   OF  THE  EMBRYO  IN   THE   FOWLJS   EGG.    637 

from  without  inward,  occupying  successively  different  parts  of  the  area 
pellucida,  and  finally  reaching  the  body  of  the  embryo,  into  which  they 
penetrate  by  its  lateral  edges. 

The  main  features  of  the  development  of  che  blood  and  blood-vessels 
are  as  follows :  First.  Their  formation  commences  in  what  afterward 
becomes  the  area  vasculosa ;  that  is,  a  part  of  the  blastoderm  lying  on 
the  surface  of  the  yolk  outside  the  body  of  the  embryo.  Secondly. 
The  walls  of  the  newly-formed  vessels,  when  they  first  become  pervious 
to  the  blood,  consist  of  a  single  layer  of  flattened  cells,  representing 
the  endothelium  of  the  adult  blood-vessels.  These  endothelial  tubes 

FIG.  191. 


AREA  VASCULOSA  OF  THE  EMBRYO  CHTCK,  after  three  and  a  half  days  of  incubation.  1, 1.  Vitel- 
line  arteries.  2,  2,  2.  Vena  terminalis.  3.  Anterior  vitelline  veins,  right  and  left.  4.  Right 
lateral  vitelline  vein.  From  preparations  by  Prof.  William  Hailes. 

extend  by  budding  and  proliferation  through  the  area  pellucida  into  the 
body  of  the  embryo,  where  they  become  continuous  with  the  endothe- 
lial lining  of  the  embryonic  blood-vessels  and  heart ;  and  the  muscular 
and  fibrous  coats,  of  the  heart  and  blood-vessels  everywhere,  are  after- 
ward produced  by  a  development  of  new  tissue  around  the  primitive 
vascular  channels.  Thirdly.  The  first  movement  of  red  blood  is  from 
the  area  vasculosa  toward  the  embryo.  For  the  heart,  when  its  pulsa- 
tions begin,  during  the  second  day  of  incubation,  contains  only  a  color- 
less fluid ;  the  red  globules  being  then  accumulated  in  the  place  of  their 
formation,  that  is,  the  meshes  of  the  area  vasculosa.  But  by  the  move- 
ment of  the  colorless  plasma,  under  the  impulsive  force  of  the  heart's 
action,  the  red  globules  become  detached  from  their  resting-places  and 
gradually  mingled  with  the  circulating  current. 

When  the  system  of  the  area  vasculosa  is  fully  established,  on  the 
third  day  of  incubation,  the  body  of  the  embryo  is  surrounded  by  a 


638  REPRODUCTION. 

vascular  plexus  in  which  the  blood  performs  a  continuous  circulatory 
movement.  The  heart  is  at  this  time  a  bent  tube  giving  origin  to  two 
main  arteries,  the  aortae,  which,  after  curving  backward,  run  on  each 
side,  for  nearly  the  whole  length  of  the  body  of  the  embryo,  beneath 
the  protovertebra,  in  the  inferior  lamina  of  the  mesoderm.  (Figs.  185 
and  186,  ao).  Near  the  posterior  extremity  of  the  provertebral  chain 
they  supplv  two  large  branches,  the  vitelline  arteries,  which  pass  out, 
one  on  each  side,  to  ramify  in  the  area  vasculosa.  When  first  formed 
these  arteries  are  of  wide  calibre,  and  their  branches  communicate  with 
each  other  by  frequent  inosculations,  both  in  the  immediate  neighbor- 
hood of  the  embryo  and  in  the  area  vasculosa.  The  vena  terminalis, 
after  making  the  circuit  of  the  area  vasculosa,  curves  backward  in  front 
of  the  embryo  on  each  side,  near  the  median  line,  forming  the  anterior 
vitelline  veins,  right  and  left.  Those  veins  are  not  only  supplied  with 
blood  from  the  vascular  plexus,  but  also  receive  inosculating  branches 
from  the  adjacent  portions  01  the  vena  terminalis.  They  continue  back- 
ward to  a  point  just  behind  the  situation  of  the  heart,  where  they 
unite  with  two  veins  coming  from  the  sides,  the  lateral  vitelline  veins, 
by  which  the  blood  is  finally  returned  from  the  area  vasculosa  to  the 
venous  extremity  of  the  heart. 

The  circulation  of  the  area  vasculosa  transfers  to  the  embryo  t  In- 
nutritious  fluids  of  the  vitellus.  The  blood  distributed  over  the  surface 
of  the  yolk  absorbs  its  organic  materials  and  returns  with  them  by  the 
vitelline  veins ;  and  by  a  continuation  of  this  movement  the  nutritive 
substances  stored  up  in  the  yolk  sac  are  utilized  for  the  growth  of  the 
embryonic  tissues.  After  the  establishment  of  this  circulation,  accord- 
ingly, the  development  of  the  embryo  goes  on  with  increased  rapidity. 
The  subsequent  changes  vary  in  different  species  and  classes  according 
to  the  final  disposition  and  relative  importance  of  various  parts ;  but  in 
all  vertebrate  animals  the  origin  and  early  formation  of  the  organs 
follow  a  similar  course  to  that  in  the  fowl's  egg  during  incubation. 


CHAPTER  VIII. 

ACCESSORY    EMBRYONIC    ORGANS;     UMBILICAL     VESI- 
CLE, AMNION,  AND   ALLANTOIS. 

THUS  far  the  process  of  development  relates  to  the  principal  parts 
of  the  body  of  the  embryo.  In  some  species  this  includes  all  the 
important  structures  in  the  impregnated  egg;  the  embryo  arriving 
very  soon  at  a  stage  of  growth  in  which  it  is  capable  of  an  independent 
existence.  But  in  many  fish  and  reptiles,  and  in  all  birds  and  mam- 
malia, additional  structures  are  produced,  which  aid  in  the  protection 
or  nutrition  of  the  embryo  during  the  middle  and  later  periods  of  its 
development.  In  these  instances  certain  portions  of  the  blastoderm, 
like  those  forming  the  area  vasculosa  in  the  fowl's  egg,  remain  outside 
the  body,  and  assume  the  function  of  accessory  organs.  The  most 
important  of  these  are  the  umbilical  vesicle,  the  amnion,  and  the 
allantois. 

Umbilical  Vesicle. 

In  the  frog's  embryo  (page  620),  the  abdominal  plates,  closing  to- 
gether in  front,  join  each  other  upon  the  median  line;  thus  shutting  in 
the  vitellus,  and  enclosing  it  in  the  future  intestinal  canal. 

In  other  instances  the  abdominal  plates  do  not  immediately  embrace 
the  whole  of  the  vitelline  mass,  but  approach  each  other  at  some  inter- 
mediate point ;  constricting  the  vitellus  and  dividing  it  by  this  means 
into  two  portions,  one  of  which  is  included 
within  the  body  of  the  embryo,  while  the  Fiq' 192' 

other  remains  outside  (Fig.  192).  As  de- 
velopment proceeds,  and  the  embryo  in- 
creases in  size,  the  constriction  becomes 
more  strongly  marked,  forming  a  nearly  com- 
plete separation  between  the  internal  and 
external  portions  of  the  vitellus.  The  in- 
ternal portion  remains  as  part  of  the  in- 
testinal canal;  while  the  external  portion,  EGG  OF  FISH,  showing  formation 

.,,.,,,  of  umbilical  vesicle. 

witn  its  blastodernnc  covering,  forms  a  sac- 
like  appendage  to  the  abdomen,  attached  at  the  umbilicus,  and  known 
as  the  umbilical  vesicle. 

The  umbilical  vesicle  is  accordingly  lined  by  a  portion  of  the  internal 
blastodermic  layer,  continuous  with  the  epithelium  of  the  intestine ; 
and  covered  by  a  portion  of  the  external  blastodermic  layer,  continuous 
with  the  integument  of  the  abdomen. 

639 


640  REPRODUCTION. 

After  the  young  animal  leaves  the  egg,  the  umbilical  vesicle  in  some 
species  becomes  shrunken  and  atrophied  by  the  absorption  of  its  con- 
tents. In  others  the  abdominal  walls  gradually  extend  over  it,  and 
crowd  it  back  into  the  abdomen ;  the  nutritious  matter  which  it  con- 
tains passing  into  the  intestine  by  the  narrow  passage  remaining 
between  them. 

In  man,  as  well  as  in  quadrupeds,  the  umbilical  vesicle  becomes  more 
completely  separated  from  the  abdomen.     There 
I'm.  193.  is  at  first  a  wide  communication  between  the  two; 

but  this  communication  is  subsequently  narrowed 
by  the  gradual  constriction  of  the  abdominal  walls, 
and  the  opposite  surfaces  of  the  canal  at  last 
come  in  contact  and  unite  with  each  other.  The 
passage  is  thus  obliterated;  and  the  umbilical 
vesicle  is  then  connected  with  the  abdomen  only 
by  an  impervious  cord.  The  cord  afterward  in- 
creases in  length,  becoming  a  slender  pedicle  (Fig. 
193),  connected  at  its  farther  extremity  with  the 
HUMAN  EMBRYo.with  um-  umbilical  vesicle,  which  is  filled  with  a  transparent, 

bilical  vesicle ;  about  the         .      .          -,    .,       „,,  ,  .,.      ,  .  ,        ,.  ,-,      , 

fifth  week.  colorless  fluid.    The  umbilical  vesicle  of  the  human 

foetus  is  distinctly  visible  until  the  end  of  the  third 
month.  After  that  period  it  diminishes  in  size,  and  is  gradually  lost 
in  the  advancing  development  of  the  neighboring  parts. 

Amnion  and  Allantois. 

The  amnion  and  allantois  are  closely  related  in  their  physiological 
importance,  since  the  first  necessarily  precedes  the  formation  of  the 
second.  The  amnion  is  developed  from  the  external  layer  of  the 
blastoderm ;  the  allantois  from  its  internal  layer.  The  amnion  is  so 
called  probably  from  the  Greek  apvis,  a  young  lamb;  from  its  having 
been  first  observed  as  a  fo3tal  envelope  in  this  animal.  The  name  of 
the  allantois  is  derived  from  the  Greek  aM-ai/toftS^,  owing  to  its  elon- 
gated or  sausage-like  form  in  some  of  the  domestic  animals. 

Both  these  organs  are  connected  with  the  nutrition  of  the  embryo 
within  the  egg.  In  birds  and  quadrupeds,  the  young  animal,  while 
still  enclosed  by  the  membranes,  reaches  a  high  grade  of  organization ; 
and  the  processes  of  absorption,  respiration,  and  exhalation  necessary 
for  its  growth  require  a  special  organ  for  their  accomplishment.  This 
organ,  which  brings  the  blood  of  the  foetus  into  relation  with  external 
sources  of  nutrition,  is  the  allantois. 

In  the  frog  and  similar  species,  the  internal  blastodermic  layer,  form- 
ing the  lining  membrane  of  the  intestine,  is  everywhere  inclosed  by 
the  external  layer,  forming1  the  integument.  But  in  the  higher  animals 
a  portion  of  tin-  internal  layer,  destined  to  produce  the  allantois,  is 
brought  into  contact  with  tin-  external  membrane  of  the  egg  for  pur- 
of  exhalation  and  absorption;  and  this  can  only  be  accomplished 


ACCESSORY    EMBRYONIC    ORGANS. 


641 


FIG.  194. 


dermic  layer,  c.  Body 
of  the  embryo,  d,  d. 
Am  niotic  folds.  e.Vi- 
telline  membrane. 


FIG.  195. 


by  opening  a  passage  for  it  through  the  external  blastodermic  layer. 
This  is  done  by  the  formation  of  the  amnion. 

Soon  after  the  body  of  the  embryo  has  been  sketched  out,  mainly 
by  the  thickening  of  a  portion  of  the  external  blastodermic  layer,  a 
secondary  fold  of  this  layer  rises  up  on  all  sides 
about  the  edges  of  the  newly-formed  embryo ;  so 
that  its  body  appears  as  if  sunk  in  a  kind  of  de- 
pression, surrounded  by  a  membranous  ridge,  as  in 
Fig.  194.  The  embryo  (c)  is  here  seen  in  profile, 
with  the  external  folds,  above  mentioned,  rising  up 
in  advance  of  the  head,  and  behind  the  posterior 
extremity.  The  same  thing  takes  place  on  the  two 

sides,   bv   the   formation   of  lateral   folds   simulta-  Diagram  of  the  FECUN- 
DATED EGG;  showing 

neously  with  the  appearance  of  those  in  front  and     the  formation  of  the 
behind.     As  these  folds  are  destined  to  form  the      amnion. -«.  viteiius. 

6.  External  blasto- 

amnion,  they  are  called  the  "amniotic  folds." 

The  amniotic  folds  continue  to  grow,  covering  the 
embryo  and  approaching  each  other  over  its  dorsal 
region  (Fig.  195).  Their  edges  afterward  come  in 
contact  and  unite  with  each  other  at  this  point  (Fig.  195,  6),  so  as  to 
shut  in  a  space  between  them  and  the  body  of  the  embryo.  This 
space,  which  contains  a  layer  of  clear  fluid,  is  the 
amniotic  cavity. 

There  now  appears  a  prolongation  or  diverticulum 
(Fig.  195,  c),  growing  from  the  posterior  portion  of 
the  intestinal  canal,  and  following  the  course  of  the 
amniotic  fold  which  has  preceded  it ;  occupying,  as  it 
protrudes,  the  space  thus  left  vacant.  This  diver- 
ticulum is  the  commencement  of  the  allantois.  It  is 
an  elongated  membranous  sac,  continuous  with  the 
posterior  portion  of  the  intestine,  and  containing  Diagram  of  the  FE- 
blood-vessels  derived  from  those  of  the  intestinal  theT™n^ed.-I" 
circulation.  Its  cavity  communicates  with  that  of  Umbilical  vesicle. 
the  intestine.  ^ZT^ 

After  the  amniotic  folds  have  approached  and 
touched  each  other  over  the  back  of  the  embryo,  their  adjacent  surfaces 
fuse  together  at  the  point  of  contact ;  so  that  the  cavities  of  the  two 
folds,  coming  respectively  from  front  and  rear,  are  separated  only  by  a 
single  membranous  partition  (Fig.  196,  c)  connecting  the  inner  and 
outer  laminae  of  the  amniotic  folds.  This  partition  is  afterward 
atrophied  and  disappears;  and  the  inner  and  outer  laminae  become 
separated  from  each  other.  The  inner  lamina  (Fig.  196,  a)  remains 
continuous  with  the  foetal  integument,  thus  enclosing  the  embryo  in 
a  distinct  cavity.  It  is  called  the  amnion,  and  its  cavity  is  known  as 
the  amniotic  cavity.  The  outer  lamina,  on  the  other  hand  (Fig.  196, 
&),  comes  in  contact  with  the  original  vitelline  membrane  and  fuses 
with  its  substance,  so  that  the  two  form  but  one.  This  membranous 

2Q 


642 


REPRODUCTION. 


layer,  resulting  from  the  consolidation  of  two  others,  then  constitutes 
the  external  investing  membrane  of  the  egg. 

The  allantois,  in  the  mean  time,  increases  in 
size  and  vascularity.  Still  following  the  course 
of  the  amniotic  folds,  it  insinuates  itself  between 
them,  until  it  comes  in  contact  with  the  external 
membrane  above  described.  It  then  begins  to 
expand  laterally,  growing  round  the  body  of  the 
embryo,  and  bringing  its  vessels  into  contact  with 
the  external  investing  membrane  of  the  egg. 

By  a  continuation  of  this  process  the  allantois 
completely  envelops  the  body  of  the  embryo ;  its 
<>PPOsite  borders   coming  in  contact  arid' fusing 
tois  nearly  complete.-*  with  each  other  over  the  dorsal  region,  in  the 
inner  lamina  of  amniotic  manner  as  the  ammotic  folds  had  previously 

fold.    6.  Outer  lamina  of  J 

amniotic  fold.  c.  Point  done  (Fig.  19 1).     It  lines  the  whole  internal  sur- 
where  the  amniotic  folds  face  of  tne  investing  membrane  with  a  flattened, 

come  in  contact.   The  al- 
lantois is  seen  penetrating   vascular  sac;   its  blood-vessels  coming  from  the 
between  the  inner  aud  interior  of  the  body  of  the  embryo,  and  its  cavity 

outer  lamina  of  the  am-  •      ••  -,i      -i     t        /•    >i_       •    ,      .•      , 

niotic  foi.N.  still  communicating  with  that  of   the  intestinal 

canal. 

It  is  evident,  accordingly,  that  there  is  a  close  connection  between 
the  formation  of  the  amnion  and  that  of  the  allantois.  It  is  by  this 
means  that  the  allantois,  which  is  originally 
an  extension  of  the  internal  blastodermic 
layer,  comes  to  be  situated  outside  the  em- 
bryo and  the  amnion,  and  is  brought  into 
relation  with  surrounding  media.  The  two 
laminae  of  the  amniotic  folds,  by  separating 
from  each  other  as  above  described,  open  a 
passage  for  the  allantois,  through  which  it 
comes  in  contact  with  the  external  membranous 
investment  of  the  egg. 

Diagram   of   the   FECUNDATED         Physiological     Action    of    the    Allantois.— 

EGG,  with  DM-  aihmtois  fuiiy   The  physiological  action  of  the  allantois,  in 

formed.— a.  Umbilical  vesicle.     .  r    \ 

b.  Amnion.  c.  Allantois.         its  simplest  character,  may  be  studied  with 
advantage  in  the  fowl's  egg,  where  it  forms 

an  extensive  and  highly  vascular  organ,  without  important  modifica- 
tion of  its  original  structure. 

The  egg  of  the  fowl  contains,  when  first  laid,  an  abundant  deposit 
of  semi-solid  albuminous  matter  in  which  tho  yolk  is  enveloped.  This 
affords,  in  connection  with  the  yolk,  a  sufficient  quantity  of  moisture 
and  organic  nutriment  for  the  growth  of  the  embryo.  The  necessary 
warmth  is  supplied  by  the  fowl  in  incubation;  and  the  atmospheric 
gases  can  pass  without  difficulty  through  the  porous  shell  and  its 
lining  membranes.  On  the  commencement  of  incubation,  a  liquefac- 
tion takes  place  in  the  albumen  above  the  blastoderm;  allowing  the 


FIG.  197. 


ACCESSORY    EMBRYONIC    ORGANS.  643 

vitellus  to  rise  toward  the  surface  by  virtue  of  its  less  specific  gravity, 
and  bringing  the  blastoderm  almost  immediately  beneath  the  lining 
membrane  of  the  shell.  The  embryo  is  thus  placed  in  a  favorable 
position  for  the  reception  of  warmth  and  other  necessary  external 
influences.  The  liquefied  albumen  is  absorbed  by  the  vitelline  mem- 
brane, and  the  yolk  becomes  larger,  softer,  and  more  diffluent  than 
before  incubation. 

In  the  earliest  stages  of  the  embryonic  circulation  the  body  of  the 
embryo  is  surrounded,  in  the  adjacent  parts  of  the  blastoderm,  by  the 
inosculating  blood-vessels  of  the  area  vasculosa  (page  637).  As 
development  proceeds,  this  area  increases  in  extent  and  its  circulation 
becomes  more  active.  It  covers  the  upper  hemisphere  of  the  yolk ; 
and  then,  passing  this  level,  embraces  more  and  more  of  its  inferior 
hemisphere,  extending  nearly  to  its  opposite  pole. 

During  this  period  the  amnion  and  the  allantois  are  in  process  of 
formation.  At  first  the  embryo  lies  upon  its  abdomen,  as  heretofore 
described ;  but,  as  it  increases  in  size,  it  alters  its  position  so  as  to  lie 
upon  its  left  side.  The  allantois,  emerging  from  the  abdominal  cavity, 
turns  upward  over  the  body  of  the  embryo,  and  comes  in  contact  with 
the  shell  membrane.  It  then  expands  in  every  direction,  toward  the 
extremities  and  down  the  sides  of  the  egg,  enveloping  the  embryo  and 
the  vitelline  sac,  and  taking  the  place  of  the  albumen  which  has  been 
liquefied  and  absorbed. 

When  the  umbilical  vesicle  is  formed,  by  the  partial  separation  of 
the  yolk  from  the  abdomen  of  the  embryo,  the  vessels  of  the  area  vas- 
culosa, at  first  distributed  over  the  yolk,  then  ramify  upon  the  surface 
of  the  umbilical  vesicle. 

At  last  the  allantois,  by  its  continued  growth,  surrounds  nearly  all 
the  remaining  parts  ;  so  that,  at  whatever  point  the  egg  may  be  opened, 
the  internal  surface  of  the  shell  membrane  is  found  to  be  lined  with  a 
vascular  expansion.  This  expansion  is  the  allantois,  supplied  by  arteries 
emerging  from  the  body  of  the  embryo. 

The  allantois  in  the  fowl's  egg  is  accordingly  adapted,  by  its  structure 
and  position,  to  perform  the  office  of  a  respiratory  organ.  The  air 
penetrates  from  without  through  the  porous  shell  and  its  lining  mem-r 
branes,  and  acts  upon  the  blood  in  the  vessels  of  the  allantois  in  the 
same  way  as  in  the  pulmonary  capillaries  of  the  adult  animal.  Exam- 
ination of  the  egg,  at  various  periods  of  incubation,  shows  that  it 
undergoes  changes  similar  to  those  of  respiration. 

The  egg,  in  the  first  place,  during  the  development  of  the  embryo, 
loses  water  by  exhalation.  This  is  not  the  result  of  simple  evaporation, 
but  depends  upon  nutritive  changes  in  the  interior  of  the  egg ;  since  it 
does  not  take  place  to  the  same  degree  in  unimpregnated  eggs,  nor  in 
those  which  are  not  incubated,  though  freely  exposed  to  the  air.  It 
is  also  essential  to  development ;  since  in  hatching  eggs  by  artificial 
warmth,  if  the  air  of  the  hatching  chamber  become  charged  with  moist- 
ure, so  as  to  retard  or  prevent  further  exhalation,  the  development  of 


644  REPRODUCTION. 

the  embryo  is  arrested.  The  loss  of  substance  during  natural  incuba- 
tion, mainly  from  the  exhalation  of  water,  has  been  found  by  Baudrimont 
and  St.  Auge*  to  be  over  15  per  cent,  of  the  entire  weight  of  the  egg. 

Secondly,  the  egg  absorbs  oxygen  and  exhales  carbonic  acid.  The 
two  observers  above  mentioned  ascertained  that  during  eighteen  days' 
incubation,  the  fowl's  egg  absorbs  nearly  two  per  cent,  of  its  weight  of 
oxygen,  while  the  carbonic  acid  exhaled  from  the  sixteenth  to  the  nine- 
teenth day  amounts  to  nearly  £  of  a  gramme  in  twenty-four  hours.  It 
is  also  observed  that  in  the  egg  during  incubation,  as  well  as  in  the 
adult  animal,  more  oxygen  is  absorbed  than  is  returned  by  exhalation 
under  the  form  of  carbonic  acid. 

The  allantois,  however,  is  not  simply  an  organ  of  respiration ;  it  also 
takes  part  in  the  absorption  of  nutritious  matter.  As  development 
advances,  the  skeleton  of  the  chick,  at  first  cartilaginous,  begins  to 
ossify.  The  calcareous  matter  necessary  for  this  process  is  in  great 
part  derived  from  the  shell.  The  shell  is  perceptibly  lighter  and  more 
fragile  toward  the  end  of  incubation  than  at  first ;  and,  at  the  same 
time,  the  mineral  constituents  of  the  embryonic  skeleton  increase  in 
quantity.  The  lime-salts,  requisite  for  ossification,  are  absorbed  from 
the  shell  by  the  vessels  of  the  allantois,  and  transferred  to  the  bones 
of  the  chick ;  so  that,  as  the  former  becomes  weaker,  the  latter  grow 
stronger.  The  diminution  in  density  of  the  shell  is  connected  not  only 
with  the  development  of  the  skeleton,  but  also  with  the  final  release  of 
the  chick  from  the  egg.  This  deliverance  is  accomplished  mainly  by 
the  chick's  movements,  which  become,  at  a  certain  period,  sufficiently 
vigorous  to  break  the  attenuated  shell.  The  first  fracture  is  generally 
accomplished  by  a  stroke  from  the  end  of  the  bill ;  and  it  is  precisely  at 
this  point  that  the  deposit  of  osseous  matter  is  most  abundant.  The 
egg-shell,  therefore,  which  at  first  serves  for  the  protection  of  the  em- 
bryo, afterward  furnishes  the  materials  which  are  to  accomplish  its  own 
demolition,  and  thus  allow  the  escape  of  the  fully  developed  chick. 

Toward  the  end  of  incubation,  the  allantois  becomes  more  adherent 
to  the  internal  surface  of  the  shell-membrane.  At  last,  when  the  chick 
at  its  full  period  of  development  leaves  the  egg,  the  allantoic  vessels 
are  torn  off  at  the  umbilicus;  and  the  allantois  is  left  behind  as  ;m 
effete  organ  in  the  cavity  of  the  abandoned  shell. 

Both  the  amnion  and  the  allantois  are,  therefore,  formations  belong- 
ing to  the  embryo,  and  constituting,  for  a  time,  accessory  parts  of  its 
organization.  Developed  from  the  peripheral  portions  of  the  blasto- 
derm, they  are  important  structures  during  the  middle  and  latter  periods 
of  incubation  ;  but  when  the  young  animal  has  become  sufficiently  devel- 
( )))(•(!  to  carry  on  an  independent  existence,  they  are  detached  from 
their  connections,  and  replaced  by  other  organs  belonging  to  the  adult 
condition. 

*  D^veloppement  du  Foetus.     Paris,  1850,  p.  143. 


CHAPTER  IX. 

MEMBRANES   OF  THE  IMPREGNATED   EGG  IN   THE 
HUMAN  SPECIES.    AMNION  AND   CHORION. 

IN  man,  as  well  as  in  many  animals,  the  foetus  is  enveloped  in  two 
membranes,  an  inner  and  an  outer,  derived  respectively  from  the 
external  and  internal  blastodermic  layers,  and  consequently  parts  of 
the  embryonic  organism.  While  the  inner  of  these  envelopes  has  the 
same  characters  in  man  as  elsewhere,  the  outer  presents  such  modifica- 
tions of  structure  as  to  have  received  a  distinct  name.  In  animals, 
therefore,  the  foetal  membranes  are  called  the  amnion  and  the  allantois ; 
in  man,  they  are  known  as  the  amnion  and  the  chorion. 

Amnion. 

The  formation  of  the  amnion  in  the  human  species  takes  place  in  the 
manner  already  described  (page  641),  namely,  by  the  growth  of  a  cir- 


FIG.  198. 


FIG.  199. 


HUMAN  EMBRYO  AND  ITS  ENVELOPES,  about 
the"  end  of  the  first  month.— 1.  Umbilical 
vesicle.  2.  Amnion.  3.  Chorion. 


HUMAN  EMBRYO  AND  ITS  ENVELOPES,  at  the  end 
of  the  third  month ;  showing  the  enlargement  of 
the  amnion. 


cumvallation  or  surrounding  fold  of  the  external  blastodermic  layer, 
which  extends  itself  in  such  a  way  that  its  edges  meet  and  coalesce 
over  the  dorsal  region,  inclosing  the  embryo  in  a  distinct  cavity. 

At  the  time  of  its  formation,  the  amnion  closely  embraces  the  body 
of  the  embryo;  the  opposite  surfaces  lying  nearly  in  contact,  with 
hardly  any  space  between  the  two.  This  space  afterward  enlarges  and 

645 


646  REPRODUCTION. 

becomes  the  amniotic  cavity,  containing  a  little  colorless,  transparent, 
serous  fluid,  the  amniotic  fluid.  But  throughout  the  earlier  periods  of 
development  the  cavity  of  the  amnion  is  small,  as  compared  with  that 
of  the  entire  egg ;  and  the  space  between  the  amnion  and  the  exter- 
nal membrane,  or  chorion  (Fig.  198),  is  occupied  by  an  amorphous 
iri'latinous  material,  in  which  the  umbilical  vesicle  and  its  stem  lie 
imbedded. 

Subsequently  the  amnion  enlarges  more  rapidly,  in  comparison  with 
the  remaining  parts  of  the  egg,  and  thus  encroaches  upon  the  layer  of 
gelatinous  material  by  which  it  is  surrounded.  At  the  same  time  the 
amniotic  fluid  increases  in  quantity  (Fig.  190) ;  so  that  a  considerable 
space  is  left  around  the  embryo,  in  which  it  is  supported  by  the  uniform 
pressure  of  the  amniotic  fluid.  The  amnion  continues  to  enlarge  at 
this  increased  rate  until  about  the  beginning  of  the  fifth  month,  when 
it  comes  in  contact  with  the  inner  surface  of  the  chorion ;  the  inter- 
vening gelatinous  material  having  by  that  time  disappeared,  or  being 
reduced  to  a  nearly  imperceptible  layer. 

Chorion. 

The  chorion,  in  the  human  species,  is  the  external  enveloping  mem- 
brane of  the  embryo.  It  originates,  like  the  allantois  in  the  lower  ani- 
mals, by  an  outgrowth  from  the  posterior  portion  of  the  alimentary 
canal,  \vhich,  insinuating  itself  between  the  lamina?  of  the  amniotic 
folds,  spreads  over  and  around  the  amnion,  so  as  to  occupy  finally  a 
position  outside  of  it.  It  there  meets  with  the  two  thin  layers  which 
have  preceded  it,  namely,  the  outer  lamina  of  the  amniotic  fold,  and 
the  original  vitelline  membrane.  But  these  layers,  ceasing  to  grow, 
while  the  new  structures  of  the  egg  are  rapidly  enlarging,  disappear 
as  distinct  membra  UPS,  and  are  replaced  by  the  chorion,  which  thus 
becomes  the  external  investment  of  the  egg. 

So  far,  the  development  of  the  chorion  is  similar  to  that  of  the  allan- 
tois. But  its  distinguishing  peculiarity  is  that,  while  extending  over 
and  around  the  other  parts,  it  does  not  present  the  form  of  a  sac  con- 
taining fluid,  but  that  of  a  vascular  sheet  or  membrane,  like  the  skin. 
On  this  account  it  is  called  the  chorion,  while  in  the  lower  animals  it 
retains  the  name  of  allantois. 

Nevertheless,  at  its  commencement,  the  chorion  is,  like  the  allantois, 
:i  hollow  membranous  sac,  the  cavity  of  which  is  continuous  with  that 
of  the  intestine.  But  this  cavity  extends  only  a  short  distance  outside 
the  body  of  the  embryo.  Beyond  this  point  its  walls  remain  in  contact 
with  each  other,  forming  a  single  membrane.  Inside  the  body  of  the 
embryo,  on  the  other  hand,  it  retains  the  sac-like  form;  and  this  por- 
tion afterward  IMTOIUPS  the  urinary  bladder.  The  rounded  cord  or 
"urachus,"  which,  in  the  adult,  runs  from  the  superior  fundus  of  the 
Madder  to  the  umbilicus,  is  the  vestige  of  the  obliterated  canal  of  the 
primitive  chorion. 

The  next  peculiarity  of  the  chorion  is,  that  it  becomes  shaggy.     Even 


MEMBRANES    OF    THE    IMPREGNATED    EGG. 


647 


FIG.  200. 


while  the  egg  is  still  very  small,  and  has  but  recently  found  its  way 
into  the  uterus,  its  exterior  is  covered  with  villi  (Fig.  198),  which 
increase  its  extent  of  surface,  and  assist  in  the  absorption  of  fluids 
from  without.      The  villi  are  at  this 
time  simple  in  form,  and  homogeneous 
in  structure. 

As  the  egg  increases  in  size,  the 
villi  elongate,  and  become  ramified  by 
the  repeated  budding  of  lateral  off- 
shoots. After  this  process  has  con- 
tinued for  some  time,  the  chorion  pre- 
sents a  uniformly  shaggy  appearance, 
owing  to  the  abundant  compound  vil- 
losities  which  cover  its  surface. 

These  villosities,  when  examined  by 
the  microscope,  have  an  exceedingly 
characteristic  appearance.  They  orig- 
inate from  the  chorion  by  a  somewhat 
narrow  stem,  and  divide  into  second- 
ary and  tertiary  branches  of  varying 
size  and  figure ;  some  filamentous, 
others  club-shaped,  many  irregularly 
swollen  at  various  points.  All  termi- 
nate by  rounded  extremities,  giving 
to  the  whole  tuft  a  resemblance  to 

some  varieties  of  sea-weed.  The  larger  trunks  and  branches  of  the 
villosity  contain  minute  nuclei,  imbedded  in  a  nearly  homogeneous,  or 
finely  granular  substratum.  The  smaller  rami- 
fications appear,  under  a  low  magnifying  power, 
simply  granular  in  texture. 

The  villi  of  the  chorion  are  different  from 
any  other  structure  in  the  body.  Whenever 
any  portion  of  a  membrane  with  villosities  of 
this  character  is  discharged  from,  or  is  found 
in,  the  cavity  of  the  uterus,  it  is  certain  that 
pregnancy  has  existed  ;  for  such  villosities  can 
only  belong  to  the  chorion,  and  the  chorion 
is  a  part  of  the  foetus.  The  presence  of  a 
shaggy  chorion  is  therefore  as  satisfactory 
proof  of  the  existence  of  pregnancy,  as  if  the 
body  of  the  foetus  itself  had  been  found. 

While  the  villosities  just  described  are  in 
process  of  formation,  the  chorion  receives  a 
supply  of  blood-vessels  from  the  body  of  the 

embryo.  The  arteries,  which  are  a  continuation  of  those  distributed 
to  the  intestine,  pass  out  along  the  canal  of  communication  to  the 
chorion  and  ramify  over  its  surface.  The  embryo  at  this  time  has 


COMPOUND  VILLOSITY  OF  THE  HUMAN 
CHORION,  ramified  extremity.  From  a 
three  months'  foetus.  Magnified  30 
diameters. 


FIG.  201. 


EXTREMITY  OF  A  VILLOSITY  OP 
THE  CHORTON,  magnified  180 
diameters ;  showing  the  blood- 
vessels in  its  interior. 


648  REPRODUCTION. 

renfhed  such  an  activity  of  growth  that  it  requires  to  be  supplied  with 
nourishment  by  means  of  vascular  absorption,  instead  of  the  slow  pro- 
cess of  imbibition  hitherto  taking  place  through  the  villi  of  the  chorion. 
The  capillary  blood-vessels,  with  which  the  chorion  is  supplied,  pene- 
trate its  villosities.  They  enter  the  base  of  each  villus,  and  following 
the  division  of  its  compound  ramifications,  reach  the  extremities  of  its 
terminal  offshoots.  Here  they  turn  upon  themselves  in  loops  (Fig. 
201),  and  retrace  their  course,  to  unite  finally  with  the  venous  trunks 
of  the  chorion. 

The  villi  of  the  chorion  are,  accordingly,  analogous  in  structure  and 
function  to  those  of  the  intestine;  their  power  of  absorption  corre- 
sponding with  the  abundance  of  their  ramifications,  and  the  extent 
of  their  vascularity. 

The  blood-vessels  of  the  chorion,  furthermore,  are  derived  from  the 
foetus;  and  all  substances  absorbed  by  them  are  transported  to  the 
interior  of  the  body,  and  used  for  the  nourishment  of  its  tissues. 
The  chorion,  therefore,  as  soon  as  its  villi  and  blood-vessels  are  com- 
pletely developed,  becomes  an  essential  organ  for  the  nutrition  of  the 
foetus,  and  the  only  means  by  which  new  material  is  introduced  from 
without. 

The  third  change  of  importance  in  the  chorion  is  that  after  being  at 
first  shaggy  throughout,  it  becomes  partially  bald.  (Fig.  199.)  This 
change  begins  about  the  end  of  the  second  month,  commencing  at  the 
point  farthest  from  the  insertion  of  the  foetal  blood-vessels.  The  vil- 
losities of  this  region  cease  growing ;  and  while  the  entire  chorion  con- 
tinues to  enlarge,  they  fail  to  keep  pace  with  its  progressive  expansion. 
They  accordingly  become  at  this  part  thinner  and  more  scattered, 
leaving  the  surface  comparatively  bald.  This  baldness  increases  in 
extent,  spreading  over  the  adjacent  portions  of  the  chorion,  until  at 
least  two-thirds  of  its  surface  have  become  nearly  or  quite  clear  of 
villosities. 

At  the  opposite  pole  of  the  egg,  namely,  that  which  corresponds  with 
the  insertion  of  the  foetal  blood-vessels,  the  villosities  of  the  chorion, 
in-toad  of  becoming  atrophied,  continue  to  grow;  and  this  portion 
becomes  even  more  shaggy  and  thickly  set  than  before.  The  conse- 
quence is  that  the  chorion  afterward  presents  a  different  appearance  in 
different  regions.  The  greater  part  is  smooth  ;  but  a  certain  portion, 
constituting  about  one-third  of  the  whole,  is  covered  with  long,  thickly- 
set,  compound  villosities.  It  is  this  thickened  portion  which  is  con- 
cerned in  the  formation  of  the  placenta;  while  the  remainder  continues 
to  be  known  under  the  name  of  the  chorion.  The  placental  portion  of 
the  chorion  becomes  distinctly  limited  in  outline  by  about  the  end 
of  the  third  month. 

The  vascularity  of  the  chorion  keeps  pace,  in  its  different  parts,  with 
1h»i  development  of  its  villosities.  As  the  villosities  shrivel  and  dis- 
appear over  a  ]»art  of  its  extent,  the  blood-vessels  with  which  they 
were  supplied  diminish  in  abundance;  and  the  smooth  portion  of  the 


MEMBRANES    OF    THE    IMPREGNATED    EGG.          649 

chorion  finally  shows  only  a  few  straggling  vessels  running  over  its 
surface,  without  any  abundant  capillary  plexus.  In  the  thickened  por- 
tion, on  the  other  hand,  the  blood-vessels  lengthen  and  ramify  to  an 
extent  corresponding  with  that  of  the  villosities  in  which  they  are 
situated.  The  arteries,  coming  from  the  foetus,  divide  into  branches 
which  penetrate  the  villi  throughout ;  forming,  at  the  placental  por- 
tion of  the  chorion,  a  mass  of  tufted  and  ramified  vascular  loops,  while 
in  the  rest  of  the  membrane  the  vascular  supply  is  comparatively 
scanty. 

The  chorion,  accordingly,  is  the  external  investing  membrane  of  the 
egg,  produced  by  an  outgrowth  from  the  body  of  the  embryo ;  and 
the  placenta,  so  far  as  it  consists  of  the  foetal  membranes,  is  a  part 
of  the  chorion,  distinguished  by  the  local  development  of  its  villi  and 
blood-vessels. 


CHAPTER    X. 


DEVELOPMENT  OF  THE  DECIDUA,  AND  ATTACHMENT 
OF  THE  FCETAL  MEMBRANES  TO   THE  UTERUS. 

IN  the  human  species,  where  the  embryo  is  developed  within  the 
uterus,  it  depends  for  its  nutrition  upon  materials  derived  from 
the  female  parent.  The  immediate  source  of  this  supply  is  the  mucous 
membrane  of  the  uterus,  which  becomes  unusually  developed  during 
gestation,  and,  when  thus  modified  in  structure,  is  known  as  the 
decidua.  It  has  received  this  name  from  the  fact  that  it  is  thrown 
off  and  discharged  at  the  same  time  that  the  foetus  and  its  membranes 
are  expelled  from  the  uterus. 

The  mucous  membrane  of  the  body  of  the  uterus,  in  the  unimpreg- 
nated  condition,  presents  a  smooth  internal  surface.  There  is  no  dis- 
tinct layer  of  connective  tissue  between  it  and  the  muscular  substance 
beneath  ;  so  that  the  mucous 

membrane  cannot  here,  as  in  FlG-  203- 

most  other  organs,  be  read- 
ily separated  by  dissection 
from  the  subjacent  parts. 
Its  structure,  however,  is 
well  marked.  It  consists, 


FTKRINE  Mucous  MEMHRAXK,  from 
the  un impregnated  uterus,  in  verti- 
cal section,  a.  Free  surface.  6.  At- 
tached surface.  Magnified  about  10 
diameters. 


UTERINE  TUBULES,  from  the  mucous  membrane  of  an 
un  impregnated  human  uterus.  Magnified  125  diam- 
eters. 


throughout,  of  tubular  follicles,  arranged  side  by  side,  perpendicularly 
to  its  free  surface.  Near  this  surface  they  are  nearly  straight ;  but 
toward  the  deeper  part  of  the  membrane,  where  they  terminate  in 
blind  extremities,  they  become  more  or  less  wavy  or  spiral  in  their 
course.  They  are  about  0.05  millimetre  in  diameter,  and  are  lined 
with  columnar  epithelium.  They  occupy  the  entire  thickness  of  the 

650 


DEVELOPMENT    OF    THE    DECIDUA.  651 

mucous  membrane,  their  closed  extremities  resting  on  the  subjacent 
muscular  tissue,  while  their  mouths  open  into  the  cavity  of  the  uterus. 
A  few  fine  blood-vessels  penetrate  the  mucous  membrane  from  below, 
and,  running  upward  between  the  tubules,  encircle  their  superficial 
extremities  with  a  capillary  network.  There  is  no  connective  tissue 
in  the  uterine  mucous  membrane,  but  only  a  few  isolated  nuclei  and 
spindle-shaped  fibre-cells  between  the  tubules. 

Decidua  Vera. — As  the  fecundated  egg  descends  through  the  Fallo- 
pian tube,  the  uterine  mucous  membrane  takes  on  an  increased  activity 
of  growth.  It  becomes  tumefied  and  vascular  ;  and,  as  it  increases  in 
thickness,  it  projects,  in  rounded  eminences,  into  the  uterine  cavity. 
(Fig.  204.)  The  uterine  tubules  increase  both  in  length  and  in  width ; 
and  their  open  mouths  become  perceptible  on  the  uterine  surface,  like 
minute  perforations.  According  to  Kolliker,  so  early  as  the  end  of  the 
first  week,  they  have  increased  to  three  or  four  times  their  original 
size,  measuring  on  the  average  0.20  millimetre  in  diameter.  The  blood- 
vessels of  the  mucous  membrane  also  enlarge  and  communicate  freely 
with  each  other  ;  the  vascular  network  between  and  around  the  tubules 
thus  becoming  more  extensive  and  abundant.  The  internal  surface  of 
the  uterus  presents  a  thick,  rich,  soft,  velvety,  and  vascular  lining,  quite 
different  from  that  found  in  the  unimpregnated  condition.  It  is  now 
known  as  the  decidua ;  and,  in  order  to  distinguish  it  from  a  similar 
growth  of  subsequent  formation,  it  has  received  the  special  name  of  the 
decidua  vera. 

The  production  of  the  decidua  is  confined  to  the  body  of  the  uterus, 
the  mucous  membrane  of  the  cervix  taking  no  part  in  the  process,  but 
retaining  its  original  appearance.  The  decidual  membrane  commences 
above,  at  the  orifices  of  the  Fallopian  tubes,  and  ceases  below,  at  the 
os  internuin.  The  cavity  of  the  cervix,  meanwhile,  is  filled  with  an 
abundant  secretion  of  viscid  mucus,  which  blocks  up  its  passage,  and 
protects  the  internal  cavity.  If  the  uterus  be  opened  in  this  condition, 
its  body  will  be  seen  lined  with  the  decidua  vera,  which  is  continuous, 
at  the  os  internum,  with  the  unaltered  mucous  membrane  of  the  cervix. 

Decidua  Eeflexa. — As  the  fecundated  egg  passes  the  lower  orifice  of 
the  Fallopian  tube,  it  insinuates  itself  between  the  opposite  surfaces  of 
the  uterine  mucous  membrane,  and  becomes  lodged  in  one  of  the  depres- 
sions between  the  folds  of  the  decidua.  (Fig.  204.)  At  this  situation 
an  adhesion  subsequently  takes  place  between  the  external  membrane 
of  the  egg  and  the  uterine  decidua.  At  the  point  where  the  egg  thus 
becomes  fixed,  there  is  a  still  more  rapid  development  of  the  uterine 
mucous  membrane.  Its  projecting  folds  grow  up  around  the  egg  in 
such  a  manner  as  to  partially  enclose  it  in  a  kind  of  circumvallation, 
and  shut  it  off,  in  great  measure,  from  the  surrounding  parts.  (Fig.  205.) 
The  egg  thus  comes  to  be  contained  in  a  cavity  of  its  own,  which  still 
communicates  for  a  time  with  the  general  cavity  of  the  uterus,  by  an 
opening  over  its  most  prominent  part.  As  the  process  goes  on,  this 
opening  becomes  narrower,  while  the  decidual  folds  approach  each  other 


652 


REPRODUCTION. 


over  the  surface  of  the  egg.  At  last  they  come  in  contact  and  unite 
with  each  other,  forming  a  kind  of  cicatrix,  which  remains  for  a  time, 
to  mark  the  situation  of  the  original  opening. 

When  the  development  of  the  uterus  has  reached  this  point  (Fig. 


FIG.  204. 


FIG.  205. 


IMPRKGNATED  UTERUS;  showing  formation  of 
decidua.  The  decidua  is  represented  in 
black ;  and  the  egg  is  seen,  at  the  fundus  of 
the  uterus,  engaged  between  two  of  its  pro- 
jecting folds. 


IMPREGNATED  UTERUS,  with  folds  of  decidua 
growing  up  around  the  egg.  The  narrow 
opening,  where  the  folds  approach  each 
other,  is  seen  over  the  most  prominent 
portion  of  the  egg. 


FIG.  206. 


206),  the  egg  is  completely  enclosed ;  being  covered  with  a  decidual 
layer  of  new  formation,  by  which  it  is  concealed  from  view  when  the 
uterine  cavity  is  laid  open.  This  newly-formed 
layer,  enveloping  the  projecting  portion  of  the 
egg,  is  called  the  Decidua  reflexa;  because 
it  is  reflected  over  the  egg  from  the  general 
surface  of  the  uterine  mucous  membrane.  The 
orifices  of  the  uterine  tubules,  in  consequence 
of  the  manner  in  which  the  decidua  reflexa 
is  formed,  are  seen  not  only  on  its  external 
surface,  or  that  which  looks  toward  the  cavity 
of  the  uterus,  but  also  on  its  internal  surface, 
or  that  which  looks  toward  the  egg. 

The  decidua  vera,  therefore,  is  the  original 
mucous  membrane  of  the  uterus.  The  decidua 
reflexa  is  a  new  formation,  which  grows  up 
around  the  egg,  to  enclose  it  in  a  distinct 
cavity. 

If  abortion  occur  at  this  time,  the  mucous  membrane  of  the  uterus, 
that  is,  the  decidua  vera,  is  thrown  off,  and  brings  with  it  the  e#g  and 
the  decidua  reflexa.  On  examining  the  mass  so  discharged,  the  egg 
will  be  found  imbedded  in  the  decidual  membrane.  One  side  of  the 
membrane,  where  it  has  been  torn  away  from  the  uterus,  is  ragged; 
the  other  side,  corresponding  to  the  uterine  cavity,  is  smooth  or  gently 
convoluted,  and  exhibits  distinctly  the  orifices  of  the  uterine  tubules; 
while  the  eirii1  itself  can  only  be  extracted  by  cutting  through  the  deeid- 


IMPREGNATKD  UTERUS;  show- 
ing the  egg  completely  en- 
closed by  the  decidua  relic  x a. 


DEVELOPMENT    OF    THE    DECIDUA.  653 

ual  membrane,  either  from  one  side  or  the  other,  and  opening  in  this 
way  the  special  cavity  in  which  it  is  enclosed. 

During  the  formation  of  the  decidua  reflexa,  the  entire  egg,  as  well 
as  the  body  of  the  uterus,  has  considerably  enlarged.  That  portion  of 
the  uterine  mucous  membrane  situated  immediately  beneath  the  egg, 
and  to  which  it  first  became  attached,  has  also  become  thicker  and  more 
vascular.  The  remainder  of  the  decidua  vera,  however,  no  longer  keeps 
pace  with  the  increasing  size  of  the  egg  and  of  the  uterus.  It  is  still 
thick  and  vascular  at  the  end  of  the  third  month ;  but  after  that  period 
it  becomes  thinner  and  less  consistent,  while  the  principal  activity  of 
growth  is  concentrated  in  that  portion  of  the  uterine  mucous  membrane 
which  is  in  immediate  contact  with  the  egg. 

Attachment  of  the  Fcetal  Membranes  to  the  Uterus. — While  the  above 
changes  are  taking  place  in  the  uterus,  the  formation  of  the  embryo, 

FIG.  207.  FIG.  208. 


IMPREGNATED  UTERUS  ;  show-  PREGNANT  UTERUS  ;  showing  the  for- 

ing  the  connection  between  mation    of    the    placenta    by  the 

the  villosities  of  the  chorion  local   development  of  the  decidua 

and  the  decidual  membranes.  and  the  chorion. 

and  the  development  of  its  membranes  have  been  going  on  simultane- 
ously ;  and  soon  after  the  entrance  of  the  egg  into  the  uterine  cavity, 
the  chorion  is  covered  with  villosities  which  insinuate  themselves  into 
the  uterine  tubules,  or  between  the  folds  of  the  decidua.  When  the 
formation  of  the  decidua  reflexa  is  complete,  the  chorion  has  become 
uniformly  shaggy ;  and  its  villosities  penetrate  both  into  the  decidua 
vera  beneath  it  and  into  the  decidua  reflexa  with  which  it  is  covered. 
In  this  way  it  becomes  everywhere  entangled  with  the  decidua,  and 
cannot  be  readily  separated  without  rupturing  some  of  the  filaments 
which  have  grown  from  its  surface  into  the  substance  of  the  decidua. 
The  nutritious  fluids,  exuded  from  the  decidua,  are  now  imbibed  by  the 
villosities  of  the  chorion ;  and  a  more  rapid  supply  of  nourishment  is 
thus  provided,  corresponding  with  the  greater  size  of  the  egg. 

Very  soon  the  activity  of  absorption  is  still  further  increased.  The 
chorion  becomes  vascular,  by  the  formation  of  blood-vessels  emerging 
from  the  embryo  and  penetrating  the  villosities  with  which  it  is  covered. 


654  REPRODUCTION. 

Each  villosity  then  contains  a  vascular  loop,  imbedded  in  its  substance, 
and  serving  to  absorb  from  the  decidua  the  materials  for  the  growth  of 
the  embryo. 

Subsequently,  the  vascular  tufts  of  the  chorion,  at  first  uniformly 
distributed  over  its  surface,  disappear  from  the  greater  part  of  its 
cxif-nt,  becoming  more  highly  developed  at  a  particular  point,  the 
situation  of  the  future  placenta.  This  is  the  spot  at  which  the  egg  is 
in  contact  with  the  decidua  vera.  Here,  both  the  decidual  membrane 
and  the  tufts  of  the  chorion  continue  to  increase  in  thickness  and  vas- 
cularity  while  elsewhere,  over  the  prominent  portion  of  the  egg,  the 
chorion  not  only  becomes  bare  of  villosities  and  comparatively  destitute 
of  blood-vessels,  but  the  decidua  reflexa,  in  contact  with  it,  also  loses 
its  activity  of  growth  and  becomes  expanded  into  a  thin  layer,  with- 
out any  remaining  trace  of  glandular  follicles. 

The  uterine  mucous  membrane  is  therefore  developed,  during  gesta- 
tion, in  such  a  way  as  to  provide  for  the  nourishment  of  the  embryo 
in  the  different  stages  of  its  growth.  At  first,  the  whole  of  it  is  uni- 
formly increased  in  thickness  (decidua  vera).  Next,  a  portion  of  it 
grows  upward  around  the  egg,  and  covers  its  projecting  surface  (decidua 
reflexa).  Afterward,  both  the  decidua  reflexa  and  the  greater  part  of 
the  decidua  vera  diminish  in  the  activity  of  their  growth,  and  lose 
their  importance  as  a  means  of  nourishment  for  the  embryo;  while 
that  part  which  is  in  contact  with  the  vascular  tufts  of  the  chorion 
continues  to  grow,  becoming  excessively  developed,  and  taking  part  in 
the  formation  of  the  placenta. 


CHAPTER  XI. 

THE   PLACENTA. 

IN  man  and  mammalians  the  embryo,  during  intra-uterme  life,  is 
dependent  upon  the  uterus  for  the  materials  of  its  growth  ;  and  this 
supply  of  nourishment  is  provided  by  means  of  two  vascular  mem- 
branes. One  of  these  membranes,  the  chorion  or  allantois,  is  an  out- 
growth from  the  embryo ;  the  other  is  the  mucous  membrane  of  the 
uterus.  By  their  more  or  less  intimate  juxtaposition,  the  fluids  tran- 
suded from  the  blood-vessels  of  the  mother  are  absorbed  by  those  of  the 
embryo,  and  a  transfer  of  nutriment  thus  takes  place  from  the  maternal 
to  the  foetal  organism. 

In  some  animals,  the  connection  between  the  maternal  and  fcetal 
membranes  is  a  simple  one.  In  the  pig,  the  uterine  mucous  membrane 
is  everywhere  uniformly  vascular;  its  only  peculiarity  consisting  in 
the  presence  of  transverse  folds,  projecting  from  its  surface,  like  the 
valvute  conniventes  of  the  small  intestine.  The  surface  of  the  allan- 
tois is  also  smooth  and  uniformly  vascular.  No  special  development 
occurs  at  any  part  of  these  membranes,  and  no  adhesion  takes  place 
between  them.  The  vascular  allantois  of  the  foetus  lies  in  simple  appo- 
sition with  the  vascular  mucous  membrane  of  the  uterus,  each  of  the 
contiguous  surfaces  following  the  undulations  of  the  other;  and  the 
transudation  and  absorption  between  the  two  sets  of  blood-vessels  pro- 
vide for  the  nutrition  of  the  foetus.  When  parturition  takes  place,  a 
moderate  contraction  of  the  uterus  is  sufficient  to  expel  its  contents ; 
the  egg  being  displaced  from  its  position  and  discharged  from  the  uterus 
without  hemorrhage  or  laceration  of  the  parts. 

In  other  instances,  there  is  a  more  intimate  connection,  at  certain 
points,  between  the  fcetal  and  maternal  structures.  In  the  cow,  sheep, 
and  ruminating  animals  generally,  the  external  membrane  of  the  egg, 
beside  being  everywhere  supplied  with  blood-vessels,  presents,  scattered 
over  its  surface,  numerous  rounded  or  oval  spots,  covered  with  thickly 
set,  tufted,  vascular  prominences.  These  spots  are  called  cotyledons, 
or  cups,  because  each  one  is  surrounded  by  a  rim  or  fold,  which  embraces 
a  corresponding  mass  projecting  from  the  inner  surface  of  the  uterus. 
This  portion  of  the  uterine  mucous  membrane  is  also  abundantly  sup- 
plied with  blood-vessels ;  and  the  vascular  tufts  of  the  foetal  membrane 
are  entangled  with  those  belonging  to  the  uterus.  There  is  no  absolute 
adhesion  between  the  two  sets  of  vessels,  but  only  an  interlacement  of 
their  ramified  extremities ;  and  by  careful  manipulation  the  foetal  por- 

655 


656  REPRODUCTION. 

tion,  with  its  villosities,  may  be  extricated  from  the  maternal  portion 
without  the  laceration  of  either. 

In  the  carnivorous  animals,  a  similar  highly  developed,  vascular  por- 
tion of  the  allantois  runs,  in  the  form  of  a  broad  belt,  round  its  middle  ; 
corresponding  in  situation  with  an  equally  developed  zone  of  the  uterine 
mucous  membrane.  Here  the  fatal  and  maternal  structures  are  mutu- 
ally adherent ;  while,  elsewhere,  over  both  extremities  of  the  egg,  they 
lie  simply  in  contact  with  each  other.  When  gestation  comes  to  an  end, 
and  the  foatus,  with  its  membranes,  is  expelled,  the  thickened  zone  of 
uterine  mucous  membrane  is  detached  at  the  same  time,  its  place  being 
afterward  made  good  by  a  new  growth. 

ID  man,  as  shown  in  the  preceding  chapter,  the  permanently  thick- 
ened portions  of  the  chorion  and  decidua  are  united  with  each  other, 
by  mutual  interpenetration,  in  a  flattened,  cake-like  mass  of  rounded 
form,  occupying  rather  less  than  one-third  of  the  surface  of  the  chorion, 
and  corresponding  to  a  similar  extent  of  the  inner  surface  of  the  uterus. 
This  mass,  consisting  of  the  foetal  and  maternal  elements  combined,  is 
the  placenta. 

The  development  of  the  placenta  takes  place  in  the  following  manner  : 

The  villi  of  the  chorion,  when  first  formed,  penetrate  the  follicles  of 
the  uterine  mucous  membrane ;  and  are  afterward  developed  into  tufted 
vascular  ramifications,  each  of  which  turns  upon  itself  in  a  loop  at  the 
farther  extremity  of  the  villus.  At  the  same  time  the  uterine  follicle, 
into  which  the  villus  has  penetrated,  enlarges  to  a  similar  extent ;  send- 
ing out  branching  diverticula,  corresponding  with  the  ramifications  of 
the  villus.  The  growth  of  the  follicle  and  that  of  the  villus  thus  go  on 
simultaneously  and  keep  pace  with  each  other ;  the  latter  constantly 
advancing  as  the  former  enlarges. 

But  it  is  not  only  the  uterine  follicles  which  increase  in  size  and  in 
complication  of  structure.  The  capillary  blood-vessels  between  them 
also  become  unusually  developed  by  enlargement  of  their  inoscula- 
tions ;  so  that  every  follicle  is  covered  with  a  network  of  dilated  capil- 
laries, derived  from  the  blood-vessels  of  the  original  decidua. 

As  the  formation  of  the  placenta  goes  on,  the  arrangement  of  the 
fcetal  blood-vessels  remains  the  same.  They  continue  to  form  vascular 
loops,  penetrating  'deeply  into  the  decidual  membrane;  only  they 
become  more  elongated,  and  their  ramifications  more  abundant  and 
tortuous.  The  maternal  capillaries,  however,  on  the  outside  of  the 
uterine  follicles,  are  considerably  altered  in  their  anatomical  relations. 
They  enlarge  in  all  directions,  and,  encroaching  upon  the  spaces  between 
them,  fuse  successively  with  each  other ;  losing  in  this  way  the  form 
of  a  capillary  network,  and  becoming  dilated  into  sinuses,  which  com- 
municate freely  with  those  in  the  walls  of  the  uterus.  As  the  original 
capillary  plexus  occupied  the  entire  thickness  of  the  hypertrophied 
decidua,  the  vascular  sinuses,  into  which  it  is  thus  converted,  are 
equally  extensive.  They  commence  at  the  uterine  surface  of  the 
placenta,  where  it  is  in  contact  with  the  muscular  walls  of  the  organ, 


THE    PLACENTA. 


657 


FIG.  209. 


EXTREMITY  OF  A  FCETAL  TUFT,  from  the  placenta 
at  term,  in  its  recent  condition. — a.  a.  Capillary 
blood-vessels.  Magnified  135  diameters. 


and  extend  through  its  whole  thickness,  to  the  outer  surface  of  the 
fetal  chorion. 

As  the  maternal  sinuses  grow  inward,  the  vascular  tufts  of  the 
chorion    grow   outward,   through 
all  parts  of  the  placenta.     In  the 
latter  periods  of  pregnancy,  the  de- 
velopment  of  blood-vessels,  both 
foetal  and  maternal,  in  the  placenta, 
is  so  excessive  that  all  the  other 
tissues,  which  originally  coexisted 
with    them,    have    nearly    disap- 
peared.    If  a  villus  from  the  foetal 
portion  of  the  placenta  be  exam- 
ined at  this  time  in  the  fresh  con- 
dition (Fig.  209),  it  will  be  seen 
that  its  blood-vessels  are  covered 
only  with  a  homogeneous  or  finely 
granular  layer,  about  ?  mmm.  in 
thickness,  in  which  are  imbedded 
small  oval  nuclei,  similar  to  those 
at  an  earlier  period  in  the  villosi- 
ties  of  the  chorion.      The  placental  villus  is  now  hardly  anything 
more  than  a  congeries  of  tortuous  vascular  loops ;  its  remaining  sub- 
stance having  been  absorbed  in  the  excessive 
growth  of  the  blood-vessels,  the  abundance  and 
development  of  which  can  be  shown  by  injec- 
tion from  the  umbilical  arteries.     (Fig.  210.) 
The  uterine  follicles  have  lost  their  original 
structure,  and  have  become  vascular  sinuses, 
surrounding  the  tufts  of  foetal  blood-vessels. 

Finally,  the  walls  of  the  foetal  blood-vessels 
having  come  into  close  apposition  with  those 
of  the  maternal  sinuses,  the  two  become  ad- 
herent and  fuse  together ;  so  that  at  last  the 
foetal  vessels  in  the  placenta  can  no  longer  be 
separated  from  the  maternal  sinuses,  without 
lacerating  either  the  one  or  the  other. 

The  placenta,  therefore,  when  perfectly 
formed,  has  the  structure  shown  in  the  accom- 
panying diagram  (Fig.  211),  which  represents 
a  vertical  section  through  its  entire  thickness, 
receiving  the  umbilical  vessels  from  the  foetus  through  the  umbilical 
cord,  and  sending  out  its  ramified  vascular  tufts  into  the  placenta.  At 
b,  b  is  the  attached  surface  of  the  decidua;  and  at  c,  c,  c,  c  are  the 
orifices  of  uterine  vessels  which  penetrate  it  from  below.  These  vessels 
enter  the  placenta  in  an  extremely  oblique  direction,  though  they  are 
represented  in  the  diagram,  for  the  sake  of  distinctness,  as  nearly  per- 

2R 


EXTREMITY  OF  A  FCETAL  TUFT 
of  the  placenta;  from  an  in- 
jected specimen.  Magnified 
40  diameters. 


At  a,  a  is  the  chorion, 


658  REPRODUCTION. 

pendicular.  Immediately  after  penetrating  the  decidua,  they  dilate  into 
the  placental  sinuses  (represented  in  the  diagram  in  black),  which  ex- 
tend through  the  whole  thickness  of  the  organ,  embracing  the  ramifica- 
tions of  the  foetal  tufts.  At  this  stage  of  completion  the  placenta  is 
essentially  a  vascular  tissue.  The  other  structures  which  originally 
entered  into  its  composition  have  disappeared,  leaving  only  the  blood- 
vessels of  the  foetus  entangled  with  and  adherent  to  the  blood-vessels 
of  the  mother. 

There  is,  however,  no  direct  communication  between  the  foetal  and 
maternal  vessels.  The  blood  of  the  foetus  is  everywhere  separated 
from  the  blood  of  the  mother  by  a  thin  partition,  resulting  from  the 


FIG.  211. 


VERTICAL  SECTION  OK  THE  PLACENTA,  showing  the  arrangement  of  the  maternal  and  total  blood- 
vessels.—o,  a.  Chorion.    b,  b.  Decidua.    c,  c,  c,  c.  Orifices  of  uterine  sinuses. 

fusion  of  four  different  membranes,  namely,  first,  the  membrane  of  the 
foetal  villus ;  secondly,  that  of  the  uterine  follicle ;  thirdly,  the  wall  of 
the  foetal  blood-vessel ;  and  fourthly,  the  wall  of  the  uterine  sinus.  But 
this  /partition  is  of  great  extent,  owing  to  the  abundant  ramification 
of  $e  foetal  vessels.  The  vascular  tufts,  in  which  the  blood  of  the  foetus 
circulates,  are  everywhere  bathed,  in  the  placental  sinuses,  with  the 
blood  of  the  m'other  ;  and  the  interchange  of  material  between  the  two, 
by  absorption  and  exhalation,  goes  on  with  corresponding  activity. 

It  is  easy  to  demonstrate  the  arrangement  of  the  foetal  tufts  in  the 
placenta.  They  can  be  seen  by  the  naked  eye,  and  may  be  readily 
traced  from  their  attachment  at  the  chorion  to  their  termination  near 
the  uterine  surface  of  the  placenta.  The  anatomical  disposition  of  the 
placental  sinuses  is  more  difficult  of  examination.  During-  life,  while 
the  placenta  is  attached  to  the  uterus,  they  are  filled  with  the  blood  of 
the  mother,  occupying  nearly  or  quite  one-half  the  mass  of  the  placenta. 


THE    PLACENTA.  659 

But  when  the  placenta  is  detached,  and  its  maternal  vessels  torn  off  at 
their  necks  (Fig.  211,  c,  c,  c,  c),  the  sinuses,  emptied  of  blood  by  the 
compression  to  which  they  are  subjected,  are  apparently  obliterated ; 
and  the  fcetal  tufts,  lying  in  contact  with  each  other,  appear  to  con- 
stitute the  whole  of  the  placental  mass.  The  existence  of  the  sinuses, 
however,  and  their  extent,  may  be  demonstrated  in  the  following 
manner : 

If  the  uterus  of  a  woman  who  has  died  undelivered  at  the  full  term 
or  thereabout,  be  opened  without  wounding  the  placenta,  this  organ 
will  be  seen  attached  to  the  uterine  surface,  with  its  vascular  con- 
nections complete.  Let  the  foetus  be  removed  by  dividing  the  umbili- 
cal cord,  and  the  uterus,  with  the  placenta  attached,  placed  under  water, 
with  its  internal  surface  uppermost.  If  a  blowpipe  be  now  inserted  into 
one  of  the  divided  vessels  of  the  uterine  walls,  and  air  forced  through 
it  under  gentle  and  steady  pressure,  it  will  inflate,  first,  the  vascular 
sinuses  of  the  uterus  ;  next,  the  deeper  portions  of  the  placenta ;  and 
lastly,  the  air-bubbles  insinuate  themselves  everywhere  between  the 
foetal  tufts,  and  appear  in  the  most  superficial  portions  of  the  placenta, 
immediately  beneath  the  chorion  (a,  a,  Fig.  211).  This  shows  that  the 
placental  sinuses,  which  communicate  with  the  uterine  vessels,  occupy 
the  entire  thickness  of  the  placenta,  and  are  equally  extensive  with  the 
tufts  of  the  chorion. 

If  the  placenta  be  detached  and  separately  examined,  it  will  be  found 
to  present  on  its  uterine  surface  a  number  of  openings,  extremely 
oblique  in  position,  and  bounded  on  one  side  by  a  thin  crescentic  edge. 
These  are  the  orifices  of  the  uterine  blood-vessels,  passing  into  the  pla- 
centa and  torn  off  at  their  necks,  as  above  described ;  and,  by  careful 
dissection,  they  are  found  to  lead  into  extensive  collapsed  cavities  (the 
placental  sinuses),  between  the  fcetal  tufts.  These  cavities  are  filled 
during  life  with  the  maternal  blood;  and  there  is  every  reason  to 
believe  that  before  delivery,  while  the  circulation  is  going  on,  the 
placenta  is  at  least  twice  as  large  as  after  it  has  been  expelled  from 
the  uterus. 

The  part  taken  by  the  placenta  in  the  development  of  the  foetus  is 
of  primary  importance.  From  the  date  of  its  formation,  about  the 
beginning  of  the  fourth  month,  it  is  the  only  channel  for  the  convey- 
ance of  nourishment  from  the  mother  to  the  foetus.  The  nutritious 
materials,  circulating  in  the  maternal  sinuses,  pass  through  the  inter- 
vening membrane,  and  enter  the  blood  of  the  foetus.  The  healthy  or 
injurious  regimen  to  which  the  mother  is  subjected  will,  accordingly, 
exert  an  influence  upon  the  child.  Even  medicinal  substances  taken 
by  the  mother,  and  absorbed  into  her  circulation,  may  transude  through 
the  placental  vessels,  and  thus  produce  their  specific  effect  on  the  foetal 
organization. 

The  placenta  is  an  organ  of  exhalation  as  well  as  of  absorption.  The 
excrementitious  matters  in  the  blood  of  the  foetus  are  undoubtedly  dis- 
posed of  in  great  measure  by  transudation  through  the  placental  ves- 


660  REPRODUCTION. 

sels,  to  be  afterward  discharged  by  the  excretory  organs  of  the  mother. 
The  mother  may  therefore  be  affected  by  influences  derived  from  the 
foetus.  It  has  been  observed  in  animals,  that  when  the  female  has  two 
successive  litters  of  young  by  different  males,  the  young  of  the  second 
litter  will  sometimes  bear  marks  resembling  those  of  the  first  male.  In 
these  instances,  the  influence  which  produces  the  mark  is  transmitted 
by  the  first  male  to  the  foetus,  from  the  foetus  to  the  mother,  and  from 
the  mother  to  the  foetus  of  the  second  litter. 

It  is  probably  through  the  placental  circulation  that  shocks  or  injuries 
inflicted  on  the  mother  produce  disturbances  in  the  nutrition  of  the  foetus. 
There  is  little  room  for  doubt  that  various  deformities  and  deficiencies 
of  the  foetus,  conformably  to  the  popular  belief,  may  originate  from  ner- 
vous impressions  experienced  by  the  mother.  The  mode  in  which  these 
influences  are  conveyed  is  not  always  easy  of  explanation.  But  it  is 
well  known  that  nervous  impressions  in  the  adult  will  often  cause  local 
derangement  of  the  circulation,  through  the  vasomotor  system,  in  the 
brain,  the  lungs,  or  the  skin.  The  uterine  circulation  is  peculiarly  sus- 
ceptible to  similar  influences,  as  shown  in  cases  of  amenorrhoea  and 
menorrhagia.  If  a  nervous  shock  to  the  mother  may  excite  premature 
contraction  in  a  pregnant  uterus  and  consequent  abortion,  it  is  un- 
doubtedly capable  of  causing  partial  or  temporary  disturbances  of  its 
vascularity.  But  the  fcetal  circulation  is  dependent,  in  great  measure, 
on  the  maternal ;  and,  as  the  nutrition  of  the  foetus  is  provided  for  by 
the  placenta,  it  will  suffer  from  derangement  of  the  placental  circula- 
tion. These  effects  may  be  manifested  either  in  the  general  atrophy 
and  death  of  the  foetus,  or  in  the  imperfect  development  of  particular 
parts ;  as  in  the  adult  a  morbid  action  may  either  operate  on  the  entire 
system,  or  be  limited  to  some  organ  especially  sensitive  to  its  influence. 


CHAPTER  XII. 


FIG.  212. 


DISCHARGE  OF  THE   FCETUS   AND   PLACENTA.    REGEN- 
ERATION OF  THE  UTERINE  TISSUES. 

DUKINGr  the  growth  of  the  embryo,  and  the  development  of  the 
placenta,  the  muscular  tissue  of  the  uterus  increases  in  thickness, 
while  the  whole  organ  enlarges,  to  accommodate  the  greater  volume 
of  its  contents.  This  unusual  growth  of  the  muscular  tissue  gives  it 
an  increased  contractile  power  sufficient  for  the  expulsion  of  the  foetus 
at  the  time  of  delivery. 

The  enlargement  of  the  amniotic  cavity,  and  the  greater  abundance 
of  the  amniotic  fluid,  provide  space  for  the  intra-uterine  movements 
of  the  foetus.  These  movements  begin  to  be  perceptible  about  the  fifth 
month,  at  which  time  the  muscular  system  is  sufficiently  developed  to 
show  a  certain  amount  of  activity.  During  the  latter  months  of  preg- 
nancy they  become  more  frequent  and  vigorous,  and  may  often  be  felt 
by  the  hand  of  the  observer  applied  over  the  region  of  the  uterus. 

The  attachment  of  the  embryo  to  the  investing  membrane  of  the 
egg  is  at  first  by  a  short  and  wide  funnel-shaped  connection,  consisting 
of  the  commencement  of  the 
chorion,  a  part  of  the  amnion, 
and  a  deposit  of  gelatinous  ma- 
terial between  the  two,  contain- 
ing the  stem  of  the  umbilical 
vesicle.  Subsequently,  as  the 
amniotic  cavity  enlarges,  the 
body  of  the  embryo  recedes  from 
the  inner  surface  of  the  chorion, 
by  the  elongation  of  its  connect- 
ing part;  and  this,  part  conse- 
quently begins  to  present  the 
appearance  of  a  cord  (Fig.  212). 
It  is  still  surrounded  with  a  thick 
layer  of  gelatinous  matter,  by 
which  it  is  separated  from  its 
amniotic  investment.  As  it 
emerges  from  the  embryo,  at  a  point  where  the  abdominal  walls  will 
afterward  close  round  it,  to  form  the  umbilicus,  it  is  known  by  the 
name  of  the  umbilical  cord.  It  contains  the  blood-vessels  passing  out 
to  the  chorion  and  placenta. 

After  the  third  month  the  umbilical  cord  and  its  blood-vessels  elon- 
gate more  rapidly  than  is  required  by  the  increased  size  of  the  amniotic 

661 


EMBRYO  AND  ITS  MEMBRANES,  in  the 
early  period  of  gestation ;  showing  the  forma- 
tion of  the  umbilical  cord. 


662 


REPRODUCTION. 


cavity.     They  consequently  become  twisted,  the  two  umbilical  arteries 
winding  round  the  vein  in  a  spiral  direction. 

The  direction  of  the  spiral  is  not  always  the  same.  Prof.  McLane 
has  recorded  observations  in  regard  to  this  point  upon  260  umbilical 
cords  at  term,  partly  in  private  practice  and  partly  at  the  Nursery 
and  Child's  Hospital,  New  York.  Of  this  number,  in  138  cases  the 
direction  of  the  spiral  was  from  left  to  right;  in  112  cases,  from  right 
to  left;  and  in  the  10  remaining  instances  it  was  doubtful,  the  twist 
being  too  imperfectly  marked  for  decision.  This  gives  nearly  the  fol- 
lowing percentage  as  the  result  of  all  the  observations : 

DIRECTION  OF  THE  TWIST  OF  THE  HUMAX  UMBILICAL  CORD. 

From  left  to  right 53  per  cent. 

From  right  to  left 43       " 

Indeterminate 4       " 

100 

There  is,  accordingly,  no  great  preponderance  in  frequency  of  the 
twist  in  either  direction.  Two  cases  of  twins  are  included  in  the 

above  list;    in   the   first   of 

F10-  213-  which   both  umbilical  cords 

turned  from  right  to  left ;  in 
the  second,  one  of  them 
turned  from  right  to  left,  the 
other  from  left  to  right.  In 
two  instances,  the  cord  pre- 
sented turns  in  opposite  di- 
rections in  dififerent  parts  of 
its  length. 

The  gelatinous  matter  de- 
posited between  the  amnion 
and  chorion  gradually  disap- 
pears over  the  greater  part 
of  these  membranes,  but  ac- 
cumulates in  the  umbilical 
cord  in  considerable  quantity, 
surrounding  the  vessels  with 
an  elastic  envelope,  which 
from  injury. 

It  is  covered  by  an  extension 
of  the  amnion,  which  is  con- 
tinuous with  the  integument  of  the  abdomen,  and  invests  the  cord 
with  an  uninterrupted  sheath  throughout  its  length. 

The  cord  also  contains  the  stem  of  the  umbilical  vesicle.  The  situa- 
tion of  this  vesicle  is  always  between  the  chorion  and  the  amnion. 
Its  pedicle  gradually  elongates  with  the  growth  of  the  umbilical  cord ; 
and  the  vesicle,  which  generally  disappears  soon  after  the  third  month, 


PREGNANT  HUMAN  UTERUS  AND  ITS  CONTENTS,  about 
the  end  of  the  seventh  month ;  showing  the  relations    protects    them 
of  the  cord,  placenta,  and  membranes.— 1.  Decidua 
vora.    2.  Decidua  reflexa.    3.  Chorion.    4.  Amnion. 


DISCHARGE    OF    THE    FCETUS    AND    PLACENTA.      663 

sometimes  remains  as  late  as  the  fifth,  sixth,  or  seventh.  According 
to  Mayer,  it  may  even  be  found,  by  careful  search,  at  the  termination 
of  pregnancy.  When  present  in  the  middle  and  latter  periods  of  ges- 
tation, it  is  a  small,  flattened  sac,  situated  beneath  the  arnnion,  on  the 
free  surface  of  the  placenta,  at  a  variable  distance  from  the  insertion 
of  the  umbilical  cord.  A  minute  blood-vessel  is  often  seen  running  to 
it  from  the  cord,  and  ramifying  upon  its  surface. 

The  decidua  reflexa,  during  the  latter  months  of  pregnancy,  is  dis- 
tended by  the  increasing  size  of  the  egg,  and  pressed  against  the 
opposite  surface  of  the  decidua  vera.  By  the  end  of  the  seventh 
month,  the  decidua  vera  and  decidua  reflexa  are  in  contact,  though 
still  distinct  and  capable  of  being  easily  separated.  After  that  time, 
they  become  confounded  with  each  other,  forming  at  last  a  thin,  friable, 
semi-opaque  layer,  in  which  no  glandular  structure  is  perceptible. 

This  is  the  condition  of  things  at  the  termination  of  pregnancy. 
Then,  the  time  for  parturition  having  arrived,  the  hypertrophied  mus- 
cular walls  of  the  uterus  contract  upon  its  contents,  expelling  the  foetus, 
together  with  its  membranes  and  the  decidua. 

In  the  human  species,  as  well  as  in  most  quadrupeds,  the  membranes 
are  usually  ruptured  during  parturition ;  and  the  foetus  escapes  first,  the 
placenta  and  appendages  following  a  few  moments  afterward.  Occa- 
sionally the  egg  is  discharged  entire,  the  foetus  being  afterward  liberated 
by  the  laceration  of  the  membranes.  In  each  case  the  mode  of  expulsion 
is  essentially  the  same. 

The  process  of  parturition  consists  in  a  separation  of  the  decidual 
membrane,  which,  on  being  discharged,  brings  away  the  ovum  with  it. 
The  greater  part  of  the  decidua  vera,  having  fallen  into  a  state  of 
atrophy  during  the  latter  months  of  pregnancy,  is  by  this  time  nearly 
destitute  of  blood-vessels,  and  separates  without  perceptible  hemor- 
rhage. The  portion  forming  the  placenta  is,  on  the  contrary,  exces- 
sively vascular ;  and  when  this  organ  is  separated,  and  its  maternal 
vessels  torn  oft7  at  their  insertion,  a  gush  of  blood  takes  place,  accom- 
panying or  immediately  following  the  birth  of  the  foetus.  This  normal 
hemorrhage,  at  the  time  of  parturition,  does  not  come  directly  from 
the  uterine  vessels.  It  consists  of  the  blood  contained  in  the  placental 
sinuses,  and  expelled  from  the  placenta  under  the  pressure  of  the 
uterus.  Since  the  blood  thus  lost  was  previously  employed  in  the 
placental  circulation,  and  since  the  placenta  is  itself  thrown  off  at  the 
same  time,  no  unpleasant  effect  is  produced  by  such  a  hemorrhage, 
because  the  quantity  of  blood  in  the  rest  of  the  vascular  system  re- 
mains the  same.  In  normal  parturition  the  lacerated  uterine  blood- 
vessels are  immediately  closed,  after  separation  of  the  placenta,  by  the 
contraction  of  the  muscular  fibres  through  which  they  pass  in  an 
oblique  direction.  Hemorrhage  in  delivery  becomes  injurious  only 
when  it  goes  on  after  separation  of  the  placenta ;  in  which  case  it  is 
supplied  by  the  mouths  of  the  uterine  blood-vessels,  left  open  by 
failure  of  the  uterine  contractions.  So  long  as  the  uterus  remains 


664 


BEPBODUCTION. 


FIG.  214. 


relaxed,  the  hemorrhage  necessarily  continues ;  but  it  is  at  once  arrested 
by  contraction  of  the  uterine  walls. 

Regeneration  of  the  Uterus  after  Delivery. — Both  the  mucous  mem- 
brane and  the  muscular  fibres  of  the  uterus  are  replaced  after  delivery 
by  tissues  of  new  formation.  The  decidua  is  discharged  at  parturition ; 
and  the  hypertrophied  muscular  tissue,  after  serving  for  the  expulsion 
of  the  foetus,  undergoes  a  process  of  retrogression  and  atrophy. 

A  remarkable  phenomenon  connected  with  the  renovation  of  the 
uterine  tissues,  is  the  appearance  in  the  uterus,  during  pregnancy,  of  a 
new  mucous  membrane,  underneath  the  old,  and  destined  to  take  the 
place  of  the  latter  after  its  discharge. 

If  the  uterus  be  examined  immediately  after  parturition,  it  will  be 
seen  that  at  the  spot  where  the  placenta  was  attached,  every  trace  of 
mucous  membrane  has  disappeared.  The  muscular  fibres  in  this  situ- 
ation are  exposed ;  and  the  mouths  of  the  ruptured  uterine  sinuses  are 
also  visible,  their  thin  edges  hanging  into  the  cavity  of  the  uterus,  and 
their  orifices  plugged  with  bloody  coagula. 

Over  the  rest  of  the  uterine  surface  the  decidua  vera  has  also  disap- 
peared. Here,  however,  notwithstanding  the  loss  of  the  original  mucous 
membrane,  the  muscular  fibres  are  covered  with  a  semi-transparent  film, 
of  whitish  color  and  soft  consistency.  This  film  is  an  imperfect  mucous 

membrane  of  new  formation, 
which  begins  to  be  produced, 
underneath  the  decidua  vera,  as 
early  as  the  beginning  of  the 
eighth  month.  The  old  mucous 
membrane,  or  decidua  vera,  is 
at  this  time  somewhat  opaque, 
and  of  a  slightly  yellowish  color, 
from  partial  fatty  degeneration. 
It  is  easily  separable  from  the 
subjacent  parts,  owing  to  the 
atrophy  of  its  vascular  connec- 
tions ;  and  the  new  mucous  mem- 
brane beneath  it  is  distinguish- 
able by  its  fresh  color  and  semi- 
transparent  aspect. 

The  mucous  membrane  of  the 
cervix  uteri,  which  takes  no  part 
in  the  formation  of  the  decidua, 
is  not  thrown  off  in  parturition.  After  delivery  it  may  be  seen  to  ter- 
minate at  the  os  internum  by  a  lacerated  edge,  where  it  was  formerly 
continuous  with  the  decidua  vera. 

Subsequently,  a  regeneration  of  the  mucous  membrane  takes  place 
over  the  whole  extent  of  the  body  of  the  uterus.  The  membrane  of 
new  formation,  already  in  existence  at  the  time  of  delivery,  becomes 
thicker  and  more  vascular;  and  glandular  tubules  are  gradually 


MUSCULAR  FlIlRESOF  THE   UNIMPREGNATED   Hu- 

MAN  UTERUS;   from  a  woman  aged  40,  dead  of 
phthisN. 


DISCHARGE    OF    THE    FOETUS    AND    PLACENTA.       665 


FIG.  215. 


oped  in  its  substance.  At  the  end  of  two  months  after  delivery,  accord- 
ing to  Longet*  and  Heschl,.f  it  has  regained  the  normal  structure  of 
uterine  mucous  membrane.  It  unites  at  the  os  internum  with  the 
mucous  membrane  of  the  cervix,  and  the  traces  of  laceration  at  this 
spot  afterward  cease  to  be  visible.  At  the  point  where  the  placenta  was 
attached,  the  regeneration  of  the 
mucous  membrane  is  less  rapid ; 
and  a  cicatrix-like  spot  is  often 
visible  at  this  situation  for 
several  months  after  delivery. 

The  first  change  in  the  mus- 
cular tissue  of  the  uterus  after  / 
delivery  consists  in  a  fatty  de-  / 
generation.  The  muscular  fibres 
of  the  unimpregnated  uterus  are 
pale,  flattened,  spindle-shaped 
bodies  (Fig.  214),  homogeneous 
or  faintly  granular  in  appearance, 
and  measuring  about  50  mmm. 
in  length.  During  gestation  they 
increase  considerably  in  size. 

Their     texture     becomes     more     MUSCULAR  FIBRES  OF  THE  HUMAN  UTERUS,  ten  days 
,  .,     .  .,.  after  parturition;  from  a  woman  dead  of  puer- 

granular  and  their  outlines  more      peral  £ver 
distinct.     An  oval  nucleus  also 

shows  itself  in  the  central  part  of  each  fibre.  The  walls  of  the  uterus, 
at  the  time  of  delivery,  are  mainly  composed  of  these  fibres,  arranged 
in  circular,  oblique,  and  longi- 
tudinal bundles. 

About  the  end  of  the  first 
week  after  delivery,  they  begin 
to  undergo  a  fatty  degeneration. 
(Fig.  215.)  Their  granules  be- 
come larger  and  more  prominent, 
soon  assuming  the  appearance 
of  fat  granules,  imbedded  in  the 
substance  of  the  fibre.  The  de- 
posit increases  in  abundance, 
and  the  granules  continue  to 
enlarge  until  they  become  con- 
verted into  fully  formed  fat  glob- 
ules, which  fill  the  interior  of 
the  fibre  more  or  less  completely, 
and  mask,  to  some  extent,  its 
anatomical  characters.  (Fig. 
216.)  The  fatty  degeneration, 

*  Trait^  de  Physiologic.     Paris,  1850,  Generation,  p.  173. 
t  Zeitschrift  der  k.  k.  Gesellschaft  der  Aerzte,  in  Wien,  1852. 


FIG.  216. 


MUSCULAR  FIBRES  OF  THE  HUMAN  UTERUS,  three 
weeks  after  parturition ;  from  a  woman  dead  of 
peritonitis. 


666  REPRODUCTION. 

thus  induced,  gives  to  the  uterus  a  softer  consistency,  and  a  pale  yel- 
lowish color,  characteristic  of  this  period.  The  altered  muscular  fibres 
are  gradually  absorbed,  giving  place  to  others  of  new  formation,  which 
already  begin  to  show  themselves  before  the  old  ones  have  disappeared. 
The  process  finally  results  in  complete  renovation  of  the  muscular  sub- 
stance of  the  uterus.  The  organ  becomes  again  reduced  in  size,  com- 
pact in  texture,  and  of  a  pale  ruddy  hue,  as  in  the  unimpregnated  con- 
dition. The  reconstruction  of  the  uterine  tissues  is  complete,  according 
to  Heschl,  about  the  end  of  the  second  month  after  delivery. 


CHAPTER  XIII. 


DEVELOPMENT  OF  THE  NERVOUS  SYSTEM,  ORGANS  OF. 
SENSE,  SKELETON,  AND  LIMBS. 

THE  first  trace  of  the  cerebro-spinal  axis  in  the  embryo  consists  of 
the  two  longitudinal  folds  of  the  external  blastodermic  layer, 
including  between  them  the  median  furrow,  known  as  the  "medullary 
groove  "  (page  630).  When  these  folds  have  united  on  the  median 
line,  converting  the  groove  into  a  canal,  the  cavity  thus  produced 
assumes  the  name  of  the  "  medullary  canal,"  within  and  around  which 
the  central  nervous  system  is  formed. 

FIG.  218. 


FIG.  217. 


FIG.  219. 


FORMATION  OP  THE 
CEREBRO  -  SPINAL 
Axis.  — a,  6.  Spinal 
cord.  c.  Cephalic  ex- 
tremity, d.  Caudal 
extremity. 


FOZTAL  PIG,  1%  centimetre  long, 
showing  the  condition  of  the 
brain  and  spinal  cord. — 1.  Hemi- 
spheres. 2.  Tubercula  quadri- 
gemina.  3.  Cerebellum.  4.  Me- 
dulla oblongata. 


FORMATION  or  THE  CERE- 
BRO-SPINAL Axis.— 1.  Vesi- 
cle of  the  hemispheres.  2. 
Vesicle  of  the  tubercula 
quadrigemina.  3.  Vesicle 
of  the  medulla  oblongata. 


Its  mode  of  formation  is  by  the  growth  of  nervous  matter  from 
the  inner  surface  of  the  medullary  canal.  The  cerebro-spinal  axis, 
accordingly,  is  at  first  a  hollow  longitudinal  cord,  varying  in  size  in 
different  regions  (Fig.  217).  Its  anterior  part  expands  into  a  bulbous 
enlargement  corresponding  to  the  brain.  Its  posterior  part,  which  rep- 
resents the  spinal  cord,  is  nearly  cylindrical,  terminating  at  its  caudal 
extremity  by  a  pointed  enlargement. 

The  next  change  is  a  division  of  the  anterior  bulbous  enlargement 
into  three  secondary  compartments,  partially  separated  from  each  other 

667 


668  REPRODUCTION. 

by  transverse  constrictions.  They  are  known  as  the  cerebral  vesicles, 
from  which  the  different  parts  of  the  encephalon  are  afterward  developed 
(Fig.  218).  The  first  or  most  anterior  vesicle  is  destined  to  form  the 
hemispheres ;  the  second  or  middle,  the  tubercula  quadrigemina ;  the 
third,  or  posterior,  the  medulla  oblongata.  All  three  vesicles  are  hol- 
low, and  their  cavities  communicate  with  each  other  through  the  inter- 
vening orifices. 

Very  soon  the  anterior  and  posterior  cerebral  vesicles  undergo  a 
further  separation.  The  anterior  vesicle  is  divided  into  two  portions, 
of  which  the  first,  or  larger,  constitutes  the  hemispheres,  while  the 
second,  or  smaller,  becomes  the  optic  thalami.  The  third  vesicle  also 

TIG.  221. 


FOWAL  PIG,  three  centimetres  long. —  HEAD  OF  FCETAI,  TIG,  nine  centimetres 

1.  Hemispheres.   2.  Tubercula  quad-  long.— 1.  Hemispheres.   3.  Cerebellum, 

rigemina.      3.  Cerebellum.     4.  Me-  4.  Medulla  oblongata. 
dulla  oblongata. 

separates  into  two  portions,  of  which  the  anterior  becomes  the  cerebel- 
lum, the  posterior  the  medulla  oblongata. 

There  are,  therefore,  at  this  time  five  cerebral  vesicles,  all  of  which 
communicate  with  each  other  and  with  the  central  cavity  of  the  spinal 
cord.  The  entire  cerebro-spinal  axis  also  becomes  strongly  curved  in 
an  anterior  direction,  corresponding  with  the  curvature  of  the  body  of 
the  embryo  (Fig.  219)  ;  so  that  the  middle  vesicle,  or  that  of  the  tuber- 
cula quadrigemina,  occupies  a  prominent  angle  at  the  upper  part  of  the 
encephalon,  while  the  hemispheres  and  the  medulla  oblongata  are  situ- 
ated below  it,  anteriorly  and  posteriorly.  The  relative  size  of  the 
various  parts  of  the  encephalon  is  very  different  from  that  in  the  adult 
condition.  The  hemispheres  are  hardly  larger  than  the  tubercula 
quadrigemina;  and  the  cerebellum  is  inferior  in  size  to  the  medulla 
oblongata.  Soon  afterward,  the  relative  position  and  volume  of  the 
parts  begin  to  alter.  The  hemispheres  and  tubercula  quadrigemina 
grow  faster  than  the  posterior  portions  of  the  encephalon ;  and  the 
cerebellum  is  doubled  backward  over  the  medulla  oblongata.  (Fig. 
220.)  Subsequently,  the  hemispheres  enlarge  more  rapidly,  growing 
upward  and  backward,  so  as  to  cover  both  the  optic  thalami  and  the 
tubercula  quadrigemina  (Fig.  221)  ;  the  cerebellum  projecting  in  the 
same  way  over  the  medulla  oblongata.  The  subsequent  development 
of  the  cmvplialon  is  mainly  a  continuation  of  the  same  process;  the 
relative  dimensions  of  the  parts  constantly  changing,  so  that  the  hemi- 
spheres become,  in  the  adult  condition  (Fig.  222),  the  largest  division 


DEVELOPMENT    OF    THE    NERVOUS    SYSTEM.         669 

of  the  encephalon,  while  the  cerebellum  is  next  in  size,  and  covers  the 
upper  portion  of  the  medulla  oblongata.  The  hemispheres  and  cere- 
bellum, which  are  at  first  smooth,  become  afterward  convoluted ;  thus 
increasing  still  farther  the  extent  of  their  nervous  matter.  In  the 
human  foetus  the  cerebral  convolutions  begin  to  appear  about  the  fifth 
month  (Longet) ;  growing  deeper  and  more  abundant  during  the 
remainder  of  foetal  lifeu 

The  lateral  portions  of  the  brain,  enlarging  at  the  same  time  more 
rapidly,  project  on  each  side  outward  and  upward ;  and  coming  in  con- 
tact with  each  other  along  the  median  line,  form  the  right  and  left 
hemispheres,  separated  by  the  longitudinal  fissure.  A  similar  growth 
in  the  spinal  cord  results  in  the  formation  of  its  two  lateral  halves, 
separated  by  the  anterior  and 
posterior  median  fissures. 
Elsewhere  the  median  fissure 
is  less  complete,  as,  for  exam- 
ple, between  the  two  lateral 
halves  of  the  cerebellum  and 
medulla  oblongata ;  but  it  ex- 
ists everywhere,  and  marks 
more  or  less  distinctly  the 
division  of  the  nervous  cen- 
tres, produced  by  the  growth 
of  their  lateral  parts.  In  this 
way  the  whole  cerebro-spinal 
axis  is  converted  into  a  double  organ,  equally  developed  on  the  right 
and  left  sides,  and  partially  divided  by  longitudinal  median  fissures, 

Organs  of  Special  Sense. — The  eye  is  formed  on  each  side  by  a  lat- 
eral offshoot  from  the  first  cerebral  vesicle.  It  is  at  first  a  hollow 
diverticulum,  the  cavity  of  which  communicates  with  that  of  the  hemi- 
sphere from  which  it  was  produced.  Afterward,  the  passage  of  com- 
munication is  filled  with  a  deposit  of  nervous  matter,  which  becomes  the 
optic  nerve.  The  globular  portion  of  the  diverticulum,  which  is  con- 
verted into  the  eyeball,  is  lined  posteriorly  by  a  thin  layer  of  nervous 
matter,  which  becomes  the  retina  ;  its  cavity  being  occupied  by  a  gela- 
tinous substance,  the  vitreous  body.  The  crystalline  lens  is  formed  in 
a  distinct  follicle,  an  offshoot  of  the  integument,  which  becomes  par- 
tially imbedded  in  the  anterior  portion  of  the  eyeball.  The  cornea  is 
also  originally  a  part  of  the  integument,  and  remains  somewhat  opaque 
until  a  late  period  of  development.  It  becomes  nearly  transparent  a 
short  time  before  birth. 

The  iris  is  a  muscular  septum,  formed  in  front  of  the  crystalline 
lens.  Its  central  opening,  which  afterward  becomes  the  pupil,  is  at 
first  closed  by  a  vascular  membrane — the  pupillary  membrane,  pass- 
ing across  the  longitudinal  axis  of  the  eye.  The  blood-vessels  of  this 
membrane,  which  are  derived  from  those  of  the  iris,  subsequently  be- 
come atrophied.  They  first  disappear  from  its  centre,  and  recede  grad- 


670  REPRODUCTION. 

ually  toward  its  circumference,  returning  upon  themselves  in  loops,  the 
convexities  of  which  are  directed  inward.  The  pupillary  membrane 
finally  becomes  atrophied,  following  in  this  process  its  receding  blood- 
vessels from  the  centre  outward.  It  has  completely  disappeared  by  the 
end  of  the  seventh  month.  (Cruveilhier.) 

The  eyelids  are  formed  by  folds  of  the  integument,  projecting  from 
above  and  below  at  the  situation  of  the  eyeball.  They  grow  so  rapidly 
during  the  second  and  third  months  that  their  margins  come  in  contact 
and  adhere  together,  so  that  at  that  time  they  cannot  be  separated 
without  violence.  They  remain  adherent  until  the  seventh  month 
(Guy),  when  they  again  separate  and  become  movable.  In  carnivorous 
animals  (dogs  and  cats),  they  remain  adherent  until  eight  or  ten  days 
after  birth. 

The  internal  ear  is  formed  by  an  offshoot  from  the  third  cerebral 
vesicle  ;  the  passage  of  communication  afterward  filling  up  by  a  deposit 
of  white  substance,  which  becomes  the  auditory  nerve.  The  tympanum 
and  auditory  meatus  are  derived  from  the  external  integument. 

Skeleton  and  Limbs. — The  spinal  column  makes  its  first  appearance 
as  a  series  of  cartilaginous  rings  deposited  round  the  "chorda  dor- 
salis  "  (page  633).  These  rings,  increasing  in  thickness  by  subsequent 
growth,  become  the  bodies  of  the  vertebrae ;  from  which  outgrowths 
afterward  take  place  in  various  directions,  forming  the  transverse, 
oblique,  and  spinous  processes  of  the  vertebras,  and  enclosing  the  spinal 
canal. 

When  the  union  of  the  dorsal  plates  on  the  median  line  fails  to 
take  place,  the  spinal  canal  remains  open  at  that  situation,  and  pre- 
sents the  malformation  known  as  spina  bifida.  This  may  consist  sim- 
ply in  a  fissure  of  the  spinal  canal,  more  or  less  extensive,  which  may 
sometimes  be  cured,  or  even  close  spontaneously ;  or  it  may  be  com- 
plicated with  imperfect  development  or  absence  of  the  spinal  cord  at  the 
same  spot,  producing  permanent  paralysis  of  the  lower  limbs. 

The  entire  skeleton  is  at  first  cartilaginous.  The  earliest  points  of 
ossification  show  themselves,  about  the  beginning  of  the  second  month, 
almost  simultaneously  in  the  clavicle  and  tho  lower  jaw.  Then  come, 
in  the  following  order,  the  femur,  humerus  and  tibia,  the  superior 
maxilla,  the  bodies  of  the  vertebra?,  the  ribs,  the  vault  of  the  cranium, 
the  scapula  and  pelvis,  the  metacarpus  and  metatarsus,  and  the 
phalanges  of  the  fingers  and  toes.  The  bones  of  the  carpus  are  all 
cartilaginous  at  birth,  and  begin  to  ossify  only  at  the  end  of  the  first 
year.  According  to  Cruveilhier,  the  calcaneum,  the  cuboid,  and  some- 
times the  astragalus,  begin  their  ossification  during  the  latter  periods 
of  foetal  life,  but  the  remainder  of  the  tarsus  is  cartilaginous  at  birth. 
The  lower  extremity  of  the  femur,  according  to  the  same  authority, 
shows  a  point  of  ossification  at  birth ;  all  the  other  extremities  of  the 
long  bones  being  still  in  a  cartilaginous  condition.  The  scaphoid  bone 
of  the  tarsus  and  the  pisiform  bone  of  the  carpus  are  the  last  to  com- 
mence their  ossification,  several  years  after  birth.  Nearly  all  the  bones 


DEVELOPMENT    OF    THE    NERVOUS    SYSTEM.         671 

ossify  from  several  distinct  points ;  the  ossification  spreading  as  the 
cartilage  increases  in  size,  and  the  bony  pieces,  thus  produced,  uniting 
with  each  other  at  a  later  period,  usually  some  time  after  birth. 

The  limbs  appear  by  a  budding  process  from  corresponding  parts  of 
the  body.  They  are  at  first  mere  rounded  elevations,  without  any 
separation  between  the  fingers  and  toes,  or  distinction  between  the 
articulations.  Subsequently  the  free  extremity  of  each  limb  becomes 
divided  into  the  phalanges  of  the  fingers  or  toes ;  and  afterward  the 
articulations  of  the  wrist  and  ankle,  knee  and  elbow,  shoulder  and  hip, 
appear  successively  from  below  upward. 

The  lower  limbs  in  man  are  less  rapid  in  development  than  the 
upper.  Both  the  legs  and  the  pelvis  are  very  slightly  developed  in 
the  early  periods  of  growth,  as  compared  with  the  spinal,  column  to 
which  they  are  attached.  The  inferior  extremity  of  the  spinal  column, 
formed  by  the  sacrum  and  coccyx,  projects  at  first  beyond  the  pelvis, 
forming  a  tail,  which  is  curled  forward  toward  the  abdomen,  and  ter- 
minates in  a  pointed  extremity.  The  entire  lower  half  of  the  body, 
with  the  spinal  column  and  appendages, 

is  also  twisted,  from  left  to  right ;  so  that     FIG.  223. 

the  pelvis  is  not  only  curled  forward,  but 
also  faces  at  right  angles  to  the  direction 
of  the  head  and  upper  part  of  the  body. 
Subsequently  the  spinal  column  becomes 
straighter  and  loses  its  twisted  form.  At 
the  same  time  the  pelvis  and  its  muscular 
coverings  grow  so  much  faster  than  the 
sacrum  and  coccyx,  that  the  latter  become 
concealed  under  the  adjoining  soft  parts, 
and  the  rudimentary  tail  disappears.  HUMAN  EMBRYQ  about  one  month 

The  integument  of  the  embryo  is  at  first  oid.-showing  the  large  size  of  the 
thin,  vascular,  and  transparent.  It  after-  ^-^l^*",*, 

Ward   becomes    thicker,    whitish,    and   more         umn ;  the  rudimentary  upper  and 

opaque.  Even  at  birth  it  is  considerably 
more  vascular  than  in  the  adult  condition, 
and  has  a  strongly  marked  ruddy  color,  due  to  its  transparency  and 
the  abundance  of  its  capillary  blood-vessels.  The  hairs  begin  to 
appear  about  the  middle  of  intra-uterine  life ;  showing  themselves 
first  on  the  eyebrows,  afterward  on  the  scalp,  trunk,  and  limbs.  The 
nails  are  in  process  of  formation  from  the  third  to  the  fifth  month  ;  and, 
according  to  Kolliker,  are  covered  with  a  layer  of  epidermis  until  after 
the  latter  period.  The  sebaceous  matter  of  the  cutaneous  glandules 
accumulates  upon  the  skin  after  the  sixth  month,  and  forms  a  whitish, 
semi-solid,  oleaginous  layer — the  vernix  caseosa,  which  is  most  abun- 
dant in  the  flexures  of  the  joints,  between  the  folds  of  the  integument, 
behind  the  ears,  and  on  the  scalp. 


CHAPTER  XIV. 


DEVELOPMENT   OF   THE  ALIMENTARY  CANAL   AND 
APPENDAGES. 

THE  alimentary  canal  is  formed,  as  already  described  (page  621),  from 
the  internal  blastodermic  layer,  surrounded  by  a  lamina  derived 
from  the  mesoderm,  which  curves  downward  and  inward,  and  is  thus 
converted  into  a  cylindrical  tube,  closed  at  both  extremities,  and  em- 
braced on  each  side  by  the  abdominal  walls.  As  the  abdominal  walls 
do  not  unite  with  each  other  on  the  median  line  until  after  the  forma- 
tion of  the  intestine,  the  abdomen  of  the  embryo  is  at  first  widely  open 
in  front,  presenting  a  long  oval  excavation,  within  which  the  intestinal 
tube  is  situated. 

Stomach  and  Intestine. — The  formation  of  the  stomach  takes  place 
in  the  following  manner:  The  alimentary  canal,  originally  straight, 
soon  presents  two  lateral  curvatures  at  the  upper  part  of  the  abdomen ; 
the  first  to  the  left,  the  second  to  the  right.  The  first  of  these  curva- 
tures becomes  expanded  into  a  wide  sac,  projecting  laterally  into  the 
left  hypochondrium,  and  forming  the  great  pouch  of  the  stomach. 
The  second  curvature,  directed  to  the  right,  marks  the  boundary 
between  the  stomach  and  the  duodenum ;  and  the  tube  at  that  point, 
becoming  constricted  and  furnished  with  an  unusually  thick  layer  of 

muscular  fibres,  is  converted 
into  the  pylorus.  Immediately 
below  the  pylorus,  the  duode- 
num again  turns  to  the  left ;  and 
similar  curvatures,  increasing 
in  number  and  complexity,  form 
the  convolutions  of  the  small 
intestine.  The  large  intestine 
assumes  a  spiral  direction ;  as- 
cending on  the  right  side,  then 
crossing  to  the  left  as  the  trans- 
verse colon,  and  again  descend- 
ing on  the  left  side,  to  terminate, 
through  the  sigmoid  flexure,  in 
the  rectum. 

The  curvatures  of  the  intes- 
tinal canal  take  place  in  an  an- 
tero-posterior,  as  well  as  in  a 
lateral  direction  (Fig.  224).  The  abdominal  walls  are  here  imperfectly 
closed,  leaving  a  wide  opening  at  a,  b,  where  the  integument  of  the 

672 


FIG.  224. 


FORMATION  ov  THK  AMMKNTARY  CANAL.— a,  ft.  Com- 
mencement of  aninion.  c.  c.  Intestine,  d.  Pha- 
rynx, e.  Urinary  bladder.  /.  Allantois  or  chorion. 
g.  Umbilical  vesk-U-. 


DEVELOPMENT  OF  THE  ALIMENTARY  CANAL.   673 

foetus  is  continuous  with  the  am n ion.  The  intestine  makes  at  first  a 
single  angular  turn  forward,  and  at  its  most  prominent  portion  gives 
off  the  stem  of  the  umbilical  vesicle  (g).  A  short  distance  below  this 
point  it  subsequently  enlarges  in  calibre,  and  the  situation  of  this 
enlargement  marks  the  commencement  of  the  colon.  The  two  por- 
tions of  the  intestine,  after  this  period,  become  widely  different  from 
each  other.  The  upper  portion,  which  is  the  small  intestine,  grows 
most  rapidly  in  the  direction  of  its  length,  becoming  a  long,  narrow, 
convoluted  tube ;  while  the  lower  portion,  which  is  the  large  intestine, 
increases  mainly  in  diameter.  The  lowermost  part  of  the  large  intes- 
tine, which  alters  least  in  form  and  position,  becomes  the  rectum.  It 
elongates  comparatively  little,  retains  its  position  for  the  most  part  on 
the  median  line,  and,  as  its  name  indicates,  continues  nearly  straight ; 
presenting  only  a  moderate  antero-posterior  curvature  corresponding 
with  the  hollow  of  the  sacrum,  and  a  slight  lateral  obliquity.  It  at 
first  forms  the  blind  extremity  of  the  large  intestine,  but  subsequently 
communicates  with  the  exterior  by  the  perforation  of  the  anus.  *Iii 
the  embryo  chick,  according  to  Burdach,*  the  perforation  of  the  anus 
takes  place  on  the  fifth  day  of  incubation ;  in  the  human  embryo  it 
appears  during  the  seventh  week.  In  certain  instances,  the  opening 
fails  to  take  place,  and  the  rectum  is  still  closed  at  birth ;  presenting 
the  malformation  known  as  imperforate  anus.  If  the  rectum  be  other- 
wise fully  developed,  it  may  sometimes  be  felt,  distended  with  meco- 
nium,  immediately  under  the  integument ;  and  an  artificial  opening 
may  be  successfully  made  by  incision  at  the  anal  region.  In  other 
cases  the  rectum  is  also  more  or  less  deficient,  the  large  intestine  ter- 
minating in  the  upper  part  of  the  pelvic  cavity. 

Just  beyond  the  point  of  junction  between  the  small  and  the  large 
intestine,  the  colon  presents  a  rounded  diverticulum,  which  increases 
in  length  until  the  ileum,  instead  of  forming  a  continuous  tube  with 
the  colon,  seems  to  join  it  by  an  oblique  lateral  insertion.  The  diver- 
ticulum of  the  colon  is  at  this  time  conical  in  shape ;  but  afterward 
that  portion  which  forms  its  free  extremity  becomes  elongated  into  the 
appendix  vermiformis;  while  the  remaining  portion  is  enlarged  into 
the  caput  coli. 

The  caput  coli  and  appendix  vermiformis  are  at  first  situated  near 
the  umbilicus ;  but  between  the  fourth  and  fifth  months  (Cruveilhier) 
their  position  is  altered,  and  they  become  fixed  in  the  right  iliac 
region.  During  the  first  six  months  the  internal  surface  of  the  small 
intestine  is  smooth.  At  the  seventh  month  the  valvulae  conniventes 
begin  to  appear,  after  which  they  increase  in  size,  though  still  com- 
paratively undeveloped  at  birth.  The  colon  is  at  first  smooth  and 
cylindrical  in  form,  like  the  small  intestine ;  its  division  into  sacculi 
by  longitudinal  and  transverse  bands  takes  place  during  the  latter  half 
of  foetal  life. 

*  Traite  de  Physiologie.     Paris,  1838,  tome  iii.,  pp.  274,  468. 
2S 


H  HI'  HO  DUCT  IOX. 


Fio.  225. 


FCETAL 


owing  the  prot 


inent  is  seen  passing  to  the  um- 
bilical vesicle,  which,  in  the  pig, 
has  a  flattened,  leaf-like  form. 


died,  and  a  cure  effected. 


After  the  small  intestine  is  formed,  it  increases  rapidly  in  length. 
It  grows,  for  a  time,  faster  than-  the  walls  of  the  abdomen;  and  as  it 
can  no  longer  be  cbiitained  in  the  abdominal  cavity,  it  protrudes, 
under  the  form  of  a  hernia,  from  the  umbilical  opening.  (Fig.  225.) 

In  the  human  embryo,  this  protrusion  con- 
tinues during  the  latter  part  of  the  second 
month.  Subsequently,  the  walls  of  the  ab- 
domen grow  more  rapidly  than  the  intes- 
tine ;  and,  gradually  enveloping  the  hernial 
protrusion,  at  last  reinclose  it  in  the  cavity 
of  the  abdomen. 

Owing  to  imperfect  development  of  the 
abdominal  walls,  and  incomplete  closure  of 
the  umbilicus,  the  intestinal  protrusion, 
which  is  normal  during  the  early  stages  of 
foetal  life,  sometimes  remains  at  birth,  pro- 
ducing congenital  umbilical  hernia.  As 

ing    loop    of    intestine,    form-     tne    partg    at    tnig    time  nave    a    natural    ten- 
lug  umbilical  hernia.    From  the 

convexity  of  the  loop  a  thin  fiia-  dency  to  unite  with  each  other,  if  the  hernial 
protrusion  be  replaced  within  the  abdomen, 
and  retained  there  by  simple  pressure  for  a 
sufficient  period,  the  defect  is  usually  rerne- 
The- conditions  are  different  in  the  adult, 
where  hernia  is  usually  due  to  gradual  yielding  of  the  fibrous  tissues 
under  pressure  from  within.  As  the  natural  period  for  the  closure  of 
the  orifices  has  passed,  though  the  intestine  may  be  retained  within 
the  abdomen,  in  such  cases,  by  mechanical  appliances,  it  again  protrudes 
when  they  are  taken  off. 

The  contents  of  the  intestine,  which  accumulate  during  foetal  life, 
vary  in  different  parts  of  the  alimentary  canal.  In  the  small  intestine 
they  are  semifluid  in  consistency,  yellowish  or  grayish-white  in  its 
upper  part,  yellow,  reddish-brown,  or  greenish-brown  below.  In  the 
large  intestine,  where  they  are  of  a  dark  greenish  color  and  pasty  in 
consistency,  they  have  received  the  name  of  meconium,  from  their 
resemblance  to  inspissated  poppy-juice.  The  meconium  contains  a 
large  quantity  of  fat,  as  well  as  various  insoluble  substances,  the  resi- 
due of  epithelial  and  mucous  accumulations.  It  exhibits  no  trace  of 
the  biliary  salts  (taurocholates  and  glycocholates)  when  examined  by 
Pettenkofer's  test ;  and  cannot  therefore  be  regarded  as  an  accumu- 
lation of  bile.  In  the  small  intestine,  on  the  contrary,  according  to 
Lehinann,  slight  traces  of  bile  may  be  detected  as  early  as  the  fifth  or 
sixth  month.  We  have  found  distinct  indications  of  bile  in  the  small 
intestine  at  birth,' but  it  is  always  in  extremely  small  quantity,  and 
sometimes  altogether  absent. 

The  contents  of  the  fo-tal  inte.-tine  are  therefore  mainly  derived  from 
its  mucous  membrane.  Even  their  yellowish  and  greenish  hue  does 
not  depend  on  the  secretions  "Of -the  .liver,  since  the  yellow  color  first 


DEVELOPMENT    OF    THE    ALIMENTARY    CANAL.       675 

appears  about  the  middle  of  the  small  intestine,  and  not  at  its  upper 
extremity.  The  material  which  afterward  accumulates  seems  to  extend 
from  this  point  upward  and  downward,  gradually  filling  the  intestine, 
and  becoming,  in  the  ileum  and  colon,  darker  colored  and  more  pasty 
as  gestation  advances. 

The  amniotic  fluid,  during  the  latter  half  of  foetal  life,  finds  its  way, 
in  greater  or  less  abundance,  into  the  stomach,  and  thence  into  the 
intestine.  Small  cheesy-looking  masses,  sometimes  found  at  birth  in 
the  fluid  contents  of  the  stomach,  are  seen  on  microscopic  examination 
to  be  portions  of  the  vernix  caseosa  exfoliated  from  the  skin  into  the 
amniotic  cavity,  and  afterward  introduced  through  the  oesophagus  into 
the  stomach.  According  to  Kolliker,  the  downy  hairs  of  the  foetus, 
exfoliated  from  the  skin,  are  often  swallowed  in  the  same  way,  and 
may  be  found  in  the  meconium. 

The  gastric  juice  is  not  secreted  before  birth ;  the  fluids  of  the  stom- 
ach being  generally  scanty  in  amount,  clear,  nearly  colorless,  and  neu- 
tral or  alkaline. 

Liver. — The  liver  is  developed  at  a  very  early  period.  Its  size  in 
proportion  to  that  of  the  entire  body  is  much  greater  in  the  early 
months  than  at  birth  or  in  the  adult  condition.  In  the  feetal  pig  the 
relative  size  of  the  liver  is  greatest  within  the  first  month,  when  it 
amounts  to  nearly  12  per  cent,  of  the  entire  bodily  weight.  Afterward 
it  grows  less  rapidly  than  other  parts,  and  its  relative  weight  dimin- 
ishes successively  to  10  per  cent,  and  6  per  cent. ;  being  reduced  before 
birth  to  3  or  4  per  cent.  In  man  the  weight  of  the  liver  at  birth  is  also 
between  3  and  4  per  cent,  of  the  entire  body. 

The  glycogenic  function  of  the  liver  commences  during  feetal  life,  and 
at  birth  its  tissue  is  abundantly  saccharine.  In  the  early  periods  of 
foetal  life,  however,  sugar  is  produced  from  other  sources  than  the  liver. 
In  very  young  foetuses  of  the  pig,  both  the  allantoic  and  amniotic 
fluids  are  saccharine  a  considerable  time  before  glucose  makes  its  appear- 
ance in  the  hepatic  tissue.  Even  the  urine,  in  half-grown  feetal  pigs, 
contains  an  appreciable  quantity  of  sugar,  and  the  young  animal  is 
normally,  at  this  period,  in  a  diabetic  condition.  The  glucose  disappears 
before  birth,  as  shown  by  Bernard,*  from  both  the  urine  and  the  amniotic 
fluid ;  while  the  liver  begins  to  produce  the  saccharine  substance  which 
it  contains  after  birth. 

Lungs,  Thorax,  and  Diaphragm  — The  anterior  portion  of  the  ali- 
mentary canal,  which  occupies  the  region  of  the  neck,  is  the  cesoph- 
agus.  It  is  straight,  and,  at  first,  very  short ;  but  it  subsequently 
increases  in  length,  simultaneously  with  the  growth  of  the  neighbor- 
ing parts.  As  the  oesophagus  lengthens,  the  lungs  begin  to  be  devel- 
oped by  a  protrusion  from  its  anterior  portion,  representing  the  com- 
mencement of  the  trachea.  This  protrusion  soon  divides  into  two 
symmetrical  branches,  which,  by  subsequent  elongation  and  subdivi- 

*  Le9ons  de  Physiologic  Experimentale.     Paris,  1855,  p.  398. 


676  REPRODUCTION. 

sion,  form  the  bronchial  tubes  and  their  ramifications.  At  first  there 
is  no  distinction  between  the  chest  and  abdomen,  and  the  lungs  conse- 
quently project  into  the  upper  part  of  the  abdominal  cavity.  Afterward, 
an  outgrowth  takes  place  on  each  side,  in  the  form  of  a  transverse  par- 
tition, which  gradually  closes  together  and  becomes  the  diaphragm, 
thus  shutting  off  the  cavity  of  the  chest  from  that  of  the  abdomen. 
Before  the  closure  of  the  diaphragm,  an  opening  exists  by  which  the 
peritoneal  and  pleural  cavities  communicate  with  each  other.  In  some 
instances  the  development  of  the  diaphragm  is  arrested  at  this  point, 
and  the  opening  remains  permanent.  The  abdominal  organs  then  par- 
tially protrude  into  the  chest,  forming  congenital  diaphragmatic  her- 
nia. The  lung  on  the  affected  side  usually  remains  in  a  state  of 
imperfect  development.  Diaphragmatic  hernia  of  this  character  is  more 
frequently  found  on  the  left  side  than  on  the  right,  and  may  sometimes 
continue  in  adult  life  without  causing  serious  inconvenience. 

Urinary  Bladder  and  Urethra. — The  urinary  bladder  originates 
from  an  outgrowth  of  the  primitive  intestine  which  at  first  appears 
as  the  allantois  (page  641).  In  the  lower  animals  this  outgrowth 
retains  everywhere  the  character  of  a  hollow  sac.  In  man,  that  por- 
tion which  is  situated  in  the  body  of  the  embryo  and  its  immediate 
vicinity  is  also  hollow ;  while  beyond  this  point  it  spreads  out  in  the 
form  of  a  single  continuous  investing  membrane — the  "  chorioii."  Its 
elongated  portion,  between  the  chorion  and  the  abdomen  of  the  foetus, 
is  the  "  umbilical  cord,"  which  at  first  contains  a  central  tubular  canal 
throughout  most  of  its  length.  This  canal  becomes  subsequently  ob- 
literated ;  the  obliteration  commencing  at  its  outer  extremity  and  thence 
extending  inward  to  the  umbilicus.  Inside  the  umbilicus  it  still  pro- 
ceeds for  a  certain  distance  and  then  ceases.  Thus  the  original  protru- 
sion of  the  intestinal  canal  within  the  abdomen,  which  gave  rise  to  the 
allantois  and  chorion,  is  divided  into  two  portions.  The  first  portion, 
immediately  connected  with  the  intestine,  remains  hollow,  and  after- 
ward forms  the  urinary  bladder.  The  second  portion,  between  the 
urinary  bladder  and  the  umbilicus,  is  consolidated  into  a  rounded  cord, 
termed  the  urachus. 

The  urinary  bladder  is  at  first  a  pyriform  sac  (Fig.  224,  e),  commu- 
nicating at  its  base  with  the  lower  portion  of  the  intestine,  and  con- 
tinuous by  its  pointed  extremity  with  the  urachus,  by  which  it  is 
attached  to  the  abdominal  walls  at  the  umbilicus.  Afterward,  the  blad- 
der loses  this  conical  figure,  and  its  superior  fundus  assumes  in  the 
adult  a  rounded  form. 

Development  of  the  Mouth  and  Face.  —  The  alimentary  canal  is  at 
first  a  cylindrical  tube,  closed  at  both  extremities.  In  the  region  of  the 
abdomen,  which  in  the  curlier  periods  of  development  occupies  nearly 
the  whole  of  the  body,  the  mcsoderm  separates,  as  previously  described 
(page  (Mf)),  into  two  laminae,  an  outer  and  an  inner.  The  outer  lamina, 
nmsiMiii.n-  of  the  external  integument  and  the  subjacent  voluntary  mus- 
cles, forms  the  parietes  of  the  abdomen.  The  inner  lamina  forms  the 


DEVELOPMENT  OF  THE  ALIMENTARY  CANAL.   677 

mucous  membrane  of  the  alimentary  canal,  with  its  covering  of  invol- 
untary muscular  fibres.  The  separation  of  these  two  laminae  leaves 
between  them  the  peritoneal  cavity. 

But  in  the  anterior  part  of  the  body  of  the  embryo,  this  separation 
does  not  take  place.  Consequently,  that  portion  of  the  alimentary 
canal,  namely,  the  oesophagus,  remains  in  contact  with  the  surround- 
ing parts ;  and  its  anterior  rounded  extremity,  the  pharynx  (Fig. 
224,  d),  lies  within  the  head,  covered  by  the  united  tissues  of  the 
middle  and  external  blastodermic  layers. 

At  this  time  there  are  formed,  on  the  sides  and  front  of  the  neck, 
four  nearly  transverse  fissures,  the  cervical  fissures,  leading  from  the 
exterior  into  the  cavity  of  the  pharynx.  These  fissures  are  analogous 
to  the  permanent  openings  at  the  sides  of  the  neck  in  fishes,  where 
the  gills  arc  located.  But  in  the  mammalian  embryo  they  have  only 
a  temporary  existence.  The  three  lower  fissures  disappear  entirely  by 
the  subsequent  adhesion  of  their  edges ;  and  in  the  chick,  according  to 
Foster  and  Balfour,  are  completely  closed  by  the  seventh  day  of  incu- 
bation. The  upper  fissure  is  converted  into  a  narrow  canal,  leading 
into  the  pharynx,  but  closed  about  its  middle  by  a  transverse  partition. 
The  outer  portion  of  this  canal  becomes  the  external  auditory  meatus ; 
the  innor  portion,  the  Eustachian  tube.  The  transverse  partition  is  the 
membrana  tympani. 

In  the  mammalian  and  human  embryo,  the  bands  of  solid  tissue 
between  the  cervical  fissures  are  connected  with  the  formation  of  the 
mouth  and  face.  By  their  increase  in  growth  they  become  more  or  less 
prominent  folds,  known  by  the  name  of  the  "  visceral  folds."  The  first 
visceral  fold  grows  rapidly  forward,  and  divides  into  two  somewhat 
diverging  processes,  which  approach  each  other  from  the  right  and  left 
sides  toward  the  median  line.  The  lower  pair  unite,  and  form  the 
inferior  maxilla.  The  upper  pair,  which  form  the  superior  maxilla, 
unite,  not  with  each  other,  but  with  an  intervening  process  which 
grows  from  above  downward,  in  the  median  line,  between  them. 

By  the  continued  growth  of  these  processes,  above  and  below,  about 
the  median  line,  there  is  included  between  them  a  depressed  space,  lined 
with  a  continuation  of  the  integument,  and  situated  immediately  in 
front  of  the  extremity  of  the  pharynx.  This  excavation  is  the  cavity 
of  the  mouth,  enclosed  on  each  side  by  the  superior  and  inferior  maxillae; 
widely  open  in  front,  but  terminating  within  by  a  blind  pit,  having  as 
yet  no  communication  with  the  alimentary  canal. 

Subsequently,  an  opening  is  formed  between  the  back  part  of  the 
mouth  and  the  cavity  of  the  pharynx,  by  a  perforation  through  the 
blastodermic  tissues  at  that  point.  This  perforation  takes  place  in  the 
human  embryo,  according  to  Burdach,*  during  the  sixth  week.  The 
opening  thus  formed  marks  the  situation  of  the  fauces  ;  and  the  ali- 
mentary canal  then  communicates  with  the  exterior.  The  epithelium 

*  TraitS  de  Physiologic.     Paris,  1838,  tome  iii.,  p.  468. 


678  REPRODUCTION. 

of  the  mouth  is  consequently  derived  from  the  external  blastodermic 
layer,  and  is  originally  continuous  with  the  epidermis ;  while  that  of 
the  pharynx  and  oesophagus,  like  the  rest  of  the  intestinal  epithelium, 
is  derived  from  the  internal  blastodermic  layer. 

The  completion  of  the  parts  about  the  mouth  is  accomplished  by  the 
continuous  development  of  the  processes  above  described,  which  grow 
together  in  such  a  way  as  to  diminish  the  size  of  the  original  orifice, 

and  to  modify  its  form  in  various  direc- 
F*G-  2>2G-  tions.      (Fig.   226.)      The  process  which 

grows  downward  in  the  median  line  from 
the  frontal  region,  is  called  the  intermax- 
illary process,  because  it  intervenes  be- 
tween those  forming  the  superior  maxilla, 
and  contains,  at  a  later  period,  the  inter- 
maxillary bones.  In  quadrupeds  the  in- 
termaxillary bones,  containing  the  upper 
incisor  teeth,  remain  distinct  from  those 
of  the  superior  maxilla,  the  line  of  demar- 

EMBRYO,  about  one  month     cation  between  them  being  indicated  by  a 
old ;  showing  the  growth  of  the     suture.     In  man,  as  a  rule,  the  maxillary 

frontal    process    downward,    and  ,  .  .,,  ,  , .  ,         , 

that  of  the  superior  and  inferior  and  intermaxillary  bones  are  consolidated 
maxillary  processes  from  the  side,  with  each  other,  the  only  permanent 
in  th  suture  being  that  on  the  median  line,  be- 

tween the  right  and  left  halves  of  the  up- 
per jaw.  According  to  Geoffroy  Saint-Hilaire,*  a  line  of  suture  some- 
times remains  between  the  intermaxillary  and  the  superior  maxillary 
bones. 

The  two  inferior  maxillary  processes  unite  with  each  other,  making 
the  lower  border  of  the  cavity  of  the  mouth,  and  form,  by  their  union 
upon  the  median  line,  the  inferior  maxilla.  In  quadrupeds  the  infe- 
rior maxillary  bones  present  a  permanent  median  suture;  but  in  man 
they  are  consolidated  into  a  single  piece  during  the  first  year  after  birth. 
As  the  intermaxillary  process  grows  from  above  downward,  it  becomes 
double  at  its  lower  extremity,  and  gives  origin  to  lateral  offshoots, 
which  curl  round  and  enclose  two  circular  orifices,  the  anterior  nares 
(Fig.  227);  the  offshoots  themselves  becoming  the  ala)  nasi.  Theif 
external  border  subsequently  adheres  to  the  superior  maxillary  process, 
leaving  only  a  curvilinear  furrow  at  the  side  of  the  nose,  to  mark  the 
place  of  consolidation.  In  many  quadrupeds,  this  furrow  remains  an 
open  fissure,  extending  outward  and  upward  from  the  orifice  of  the 
nostril. 

The  mouth  at  this  time  is  wide  and  gaping,  owing  to  the  incomplete 
development  of  the  upper  and  lower  jaw  and  the  comparative  insuf- 
ficiency of  the  lips  and  cheeks.  The  soft  parts  afterward  increase  in 
growth,  and  thus  gradually  diminish  the  size  of  the  orifice  (Fig.  228). 

*  Histoire  des  Anomalies  de  I'Orgunization.     Paris,  1832,  tome  i.,  p.  581. 


DEVELOPMENT    OF    THE    ALIMENTARY    CANAL.      679 

The  lips  and  cheeks  arise  by  folds  of  the  integument  and  subjacent  mus- 
cular layers,  which,  projecting  downward,  upward,  and  forward,  form 
the  permanent  borders  of  the  mouth.  The  upper  lip  in  man  presents  a 
median  furrow,  bordered  by  two  slightly  elevated  ridges,  corresponding 
with  the  union  of  the  maxillary  and  intermaxillary  processes.  The 
lower  lip,  like  the  inferior  maxilla,  is  consolidated  on  the  median  line, 
and  shows  no  trace  of  its  double  origin. 

In  some  instances,  the  superior  maxillary  and  intermaxillary  pro- 
cesses fail  to  unite  with  each  other,  giving  rise  to  the  malformation 
known  as  hare-lip.  The  fissure,  in  cases  of  hare-lip,  is  consequently 


HEAD  OF  HUMAN  EMBRYO  at  about  HEAD  OF  HUMAN  EMBRYO,  about  the 

the  sixth  week.    From  a  specimen  end  of  the  second  month.    From  a 

in  the  author's  possession.  specimen  in  the  author's  possession. 

situated,  as  a  rule,  not  in  the  median  line,  but  a  little  on  one  side,  cor- 
responding with  the  outer  edge  of  the  intermaxillary  process.  Some- 
times the  deficiency  exists  on  both  sides  at  once,  forming  "  double  hare- 
lip ;"  in  which  case,  if  the  fissure  extend  through  the  bony  structures, 
the  central  piece  of  the  superior  maxilla,  detached  from  the  remainder, 
contains  the  upper  incisor  teeth,  and  corresponds  with  the  intermaxillary 
bone  of  the  lower  animals.  In  one  instance,  observed  by  Wyman,* 
the  fissure  of  hare-lip  was  situated  in  the  median  line,  the  two  inter- 
maxillary bones  not  having  united  with  each  other. 

The  eyes  at  an  early  period  are  upon  the  sides  of  the  head  (Fig.  226). 
As  development  proceeds,  they  come  to  be  situated  farther  forward 
(Fig.  221),  looking  obliquely  outward.  At  a  still  later  period  they  are 
placed  on  the  anterior  plane  of  the  face  (Fig.  228),  with  their  axes 
nearly  parallel  and  looking  forward.  .  This  change  is  effected  by  the 
more  rapid  growth  of  the  posterior  and  lateral  portions  of  the  head, 
which  enlarge  in  such  a  manner  as  to  alter  the  relative  position  of  the 
parts  in  front.  x 

The  palate  is  formed  by  the  growth  of  a  horizontal  partition  between 
the  mouth  and  nares,  which  arises  on  each  side  as  an  offshoot  from  the 
superior  maxilla.  The  twx>  .plates  afterward  unite  on  the  median  line, 

*  Transactions  of  the  Boston  Society  for  Medical  Improvement,  March  9th,  1863. 


680  REPRODUCTION. 

forming  a  complete  separation  between  the  oral  and  nasal  cavities. 
The  right  and  left  nasal  passages  are  separated  from  each  other  by  a 
vertical  plate  (vomcr),  which  grows  from  above  and  fuses  with  the 
palatal  plates  below.  Fissure  of  the  palate  is  caused  by  a  deficiency 
of  one  of  the  horizontal  plates.  It  is  accordingly  situated  a  little  on 
one  side  of  the  median  line,  and  is  frequently  associated  with  hare-lip 
and  fissure  of  the  upper  jaw. 

The  anterior  and  posterior  arches  of  the  palate  are  incomplete  trans- 
verse partitions  which  grow  from  the  sides  of  the  fauces,  subsequently 
to  the  perforation  of  the  pharynx  and  its  communication  with  the  oral 
cavity.  Owing  to  the  muscular  tissue  which  they  contain,  the  orifice 
of  the  alimentary  canal  thus  becomes  capable  of , constriction  or  enlarge- 
ment, according  to  its  condition  of  functional  activity. 


CHAPTER   XV. 

DEVELOPMENT  OF  THE  WOLFFIAN  BODIES,  KIDNEYS, 
AND  INTERNAL   ORGANS  OF  GENERATION. 

THE  first  trace  of  a  urinary  apparatus  consists  of  two  elongated, 
fusiform  organs,  which  make  their  appearance  in  the  abdomen  at 
a  very  early  period,  one  on  each  side  the  spinal  column,  known  as  the 
Wolffian  bodies.  They  are  fully  formed,  in  the  human  embryo,  toward 
the  end  of  the  first  month  (Coste),  at  which  time  they  are  the  largest 
organs  in  the  abdomen,  extending  from  just  below  the  heart  nearly  to 
the  posterior  extremity  of  the  body.  In  the  foetal  pig,  when  thirteen  or 
fourteen  millimetres  in  length,  they  are  rounded  and  kidney-shaped,  and 
occupy  a  large  part  of  the  abdominal  cavity. 

Their   combined  weight   is   a   little   over   three    FIG-  329. 

per  cent,  of  the  entire  body  ;  a  proportion  seven 
or  eight  times  as  large  as  that  of  the  kidneys  in 
the  adult  condition.  There  are  at  this  period 
only  three  organs  of  noticeable  size  in  the  abdo- 
men, namely,  the  liver,  at  the  upper  part  of  the 
abdominal  cavity ;  the  intestine,  which  is  already 
somewhat  convoluted,  and  occupies  a  central 
position ;  and  the  Wolffian  bodies  on  each  side 

the  Spinal  Column.  F(ETAI'  ^  13 

mu     TTT    iic        IT         •     xi     •     •    >.•  loug;  the  abdominal  walls 

The  Wolman  bodies,  in  their  intimate  structure,  cut  away,  to  show  the  posi- 
closely  resemble  the  adult  kidney.  Thev  consist  tion  of  the  Wolffian  bodies. 
of  secreting  tubules,  lined  with  epithelium,  run-  ^^\^JffSSL 
ning  transversely  to  the  outer  edges  of  the  organs,  4.  Wolffian  body, 
where  they  terminate  by  rounded  dilatations. 
In  each  of  these  dilated  extremities  is  a  globular  coil  of  capillary  blood- 
vessels, similar  to  the  glomerulus  of  the  kidney.  At  the  inner  edge 
of  the  Wolffian  body  the  tubules  empty  into  a  common  excretory  duct, 
which  leaves  the  organ  at  its  lower  extremity,  and  communicates  with 
the  intestinal  canal,  at  a  point  where  the  urinary  bladder  is  afterward 
situated.  The  principal  distinction  in  structure,  between  the  Wolffian 
bodies  and  the  kidneys,  consists  in  the  size  of  their  tubules  and  glom- 
eruli.  In  the  foetal  pig,  when  three  or  four  centimetres  in  length,  the 
tubules  of  the  Wolffian  body  are  0.125  millimetre  in  diameter;  while 
those  of  the  kidney  in  the  same  foetus  are  only  0.034  millimetre.  The 
glomeruli  of  the  Wolffian  bodies  are  0.55  millimetre  in  diameter,  while 
those  of  the  kidney  measure  only  0.14  millimetre.  The  Wolffian  bodies 
are  therefore  urinary  organs,  so  far  as  regards  their  minute  structure, 

681 


682  REPRODUCTION. 

Mini  aro  sometimes  known  by  the  name  of  the  "  false  kidneys."  There 
is  little  doubt  tlisit  they  perform,  at  this  period,  a  function  analogous  to 
that  (if  the  kidm-vs.  ;md  separate  from  the  blood  of  the  embryo  an 
e.\erem<'iititious  fluid  which  is  discharged  into  the  cavity  of  the  allantois. 
Subsequently,  the  Wolffian  bodies  increase  in  size;  but  as  they 
less  rapidly  than  the  other  organs,  their  relative  magnitude  dimin- 
Still  later,  they  suffer  an  absolute  atrophy,  and  become  less  per- 
ceptible. In  the  human  embryo,  they  are  hardly  visible  after  the  second 
month  (Longet),  and  in  the  quadrupeds  they  disappear  long  before 
birth. 

The  kidneys  are  formed  just  behind  the  Wolffian  bodies,  by  which 
they  are  at  first  concealed  in  a  front  view,  the  kidneys  being  at  this 

time  not  more  than  one-fourth  or  one-fifth 

FIG.  230.      part  the  size  of  the  Wolffian  bodies.     (Fig. 

230.)    The  kidneys  subsequently  enlarging, 
while  the  Wolffian  bodies  diminish,  the  pro- 
portion between  the  two  organs  is  reversed  ; 
and   the  Wolffian   bodies   appear   as   small 
ovoid  or  fusiform  masses,  on  the  anterior 
surface  of  the  kidneys  (Figs.  231  and  232). 
As  the  kidneys  grow  more  rapidly  in  an 
upward    than   a   downward   direction,    the 
Wolffian  bodies  come  to  be  situated  near 
their  inferior  extremity. 
L  PIG,  sHcentimetres  ion*.-         Thc  kidneys,  during  the  succeeding  periods 
i.  Wuiffian  body.  2.  Kidney.        of  foatal  life,  become  very  largely  developed 
in  proportion  to  the  rest  of  the  internal  or- 
gans;  attaining  a  size,  in  the  foetal  pig,  equal  to  more  than  two  per 
cent,  of  the  entire  body.    This  proportion  again  diminishes  before  birth, 
owing  to  the  increased  development  of  other  parts.     In  the  human 
foetus  at  birth,  the  weight  of  the  two  kidneys  together  is  six  parts  per 
thousand  of  the  entire  body. 

Internal  Organs  of  Generation. — About  the  same  time  with  the 
formation  of  t!io  kidneys,  two  oval-shaped  organs  make  their  appear- 
ance in  front,  on  the  inner  side  of  the  Wolffian  bodies.  These  are  the 
internal  organs  of  generation;  namely,  the  testicles  in  the  male,  and 
the  ovaries  in  the  female.  At  first  they  occupy  the  same  situation  and 
present  the  same  appearance,  whether  the  foetus  be  male  or  female  (Fiir. 
231). 

A  short  distance  above  the  internal  organs  of  generation  there  com-1 
metiers,  on  each  side,  a  narrow  tube  which  runs  downward,  parallel 
with  tin-  excretory  duct  of  the  Wolffian  body.  The  two  tubes  approach 
earh  other  In-low:  and,  joining  upon  the  median  line,  empty  into  the 
of  tin-  allantois,  or  what  will  afterward  be  the  urinary  bladder. 
Thrse  tubes  M Tve  M  the  excretory  ducts  of  the  inter n!jjil ;  organs  of 
-(•Deration  ;  afterward  becoming  the  rr/.sv/  <lr/rrentia  in  the  male,  and 
the  /'V///oy,/V///  ////»-s  in  the  female.  According  to  (\iste,  the  vasa 


DEVELOPMENT    OF    THE    WOLFFIAN    BODIES,  ETC.      683 


FIG.  231. 


INTERNAL  ORGANS  OF  GENERA- 
TION, in  a  foetal  pig  7J^  centi- 
metres long. — 1,  1.  Kidneys.  2, 
2.  Wolffian  bodies.  3,  3.  Internal 
organs  of  generation ;  testicles 
or  ovaries.  4.  Urinary  bladder, 
turned  over  in  front.  5.  Intes- 
tine. 


deferentia  at  an  early  period  are  disconnected  from  the  testicles ;  origi- 
nating, like  the  Fallopian  tubes,  by  free  extremities,  with  an  open  orifice. 
Afterward  they  become  adherent  to  the  testicles,  and  establish  a  com- 
munication with  the  tubuli  seminiferi.  In  the  human  female,  the  Fal- 
lopian tube  remains  disconnected  from  the 
ovary,  except  at  one  point  of  its  fimbriated 
extremity  ;  but  in  many  animals  the  greater 
part  of  this  extremity  becomes  adherent  to 
the  ovary,  which  it  envelops  more  or  less 
completely  in  a  distinct  sac. 

Male  Organs  of  Generation;  Descent  of 
the  Testicles. — In  the  male  foetus  there  now 
commences  a  change  in  position  of  the  in- 
ternal organs  of  generation,  known  as  the 
"descent  of  the  testicles."  In  consequence 
of  this  change,  the  testicles,  which  are  at 
first  in  front  of  the  kidneys,  near  the  middle 
of  the  abdomen,  come  to  be  situated  in  the 
scrotum,  outside  the  abdominal  cavity,  and 
enclosed  in  a  distinct  sac,  the  tunica  vagi- 
naJis  testis.  This  apparent  movement  re- 
sults from  a  disproportionate  growth  of  the  abdominal  organs  above 
the  testicles,  by  which  their  relative  position  becomes  altered. 

By  the  upward  enlargement  of  the  kidneys,  both  the  Wolffian  bodies 
and  the  testicles  are  made  to  occupy 
an  inferior  position  (Fig.  232).  At 
the  same  time,  a  slender  rounded 
cord  (not  represented  in  the  figure) 
passes  from  the  lower  extremity  of 
each  testicle  outward  and  downward, 
crossing  the  vas  deferens  a  short  dis- 
tance above  its  union  with  that  of 
the  opposite  side.  Below  this  point, 
the  cord  spoken  of  continues  to  run 
obliquely  outward  and  downward ; 
and,  passing  through  the  inguinal 
canal,  is  inserted  into  the  subcuta- 
neous tissue  near  the  symphysis 
pubis.  The  lower  part  of  this  cord 
becomes  the  gubernaculum  testis. 
It  contains  muscular  fibres,  which 

are  easily  detected,  in  the  human  foetus,  during  the  latter  half  of  intra- 
uterine  life.  At  the  period  of  birth,  or  soon  after,  they  have  usually 
disappeared. 

That  portion  of  the  excretory  tube  of  the  testicle  situated  outside 
the  crossing  of  the  gubernaculum,  becomes  afterward  convoluted,  and 
converted  into  the  epididymis.  Inside  this  point  the  tube  remains 


FIG.  232. 


INTERNAL  ORGANS  OP  GENERATION  in  a  fetal 
pig  nearly  10  centimetres  long. — 1,  1.  Kid- 
neys. 2,  2.  Wolffian  bodies.  3,  3.  Testicles. 
4.  Urinary  bladder.  5.  Intestine. 


684  REPRODUCTION. 

comparatively  straight,  but  increases  in  length,  and  is  finally  known  as 
the  vas  deferens. 

As  the  testicles  descend  still  farther  in  the  abdomen,  they  continue 
to  grow,  while  the  Wolffian  bodies  become  smaller ;  and  at  last,  when 
the  testicles  have  arrived  at  the  internal  inguinal  ring,  the  Wolffian 
bodies  arc  no  longer  recognizable.  In  the  human  foetus,  the  testicles 
reach  the  internal  inguinal  ring  about  the  end  of  the  sixth  month 
•  Wilson). 

During  the  seventh  month  a  protrusion  of  the  peritoneum  takes  place 
through  the  inguinal  canal,  in  advance  of  the  testicle;  and  as  this 
organ  passes  into  the  scrotum,  loops  of  muscular  fibres  are  given  off 
from  the  lower  border  of  the  internal  oblique  muscle  of  the  abdomen, 
ex  tending  downward  over  the  testicle  and  spermatic  cord.  They  form 
afterward  the  cremaster  muscle. 

At  last,  the  testicles  descend  quite  to  the  bottom  of  the  scrotum. 
The  convoluted  portion  of  the  efferent  duct,  namely,  the  epididymis, 
remains  attached  to  the  testicle ;    while  the  vas  deferens  passes  up- 
ward, in  a  reverse  direction,  enters  the  abdomen  through  the  inguinal 
canal,  again  bends'  downward,  and  joins  its  fellow  of  the  opposite 
side;   after  which  they  both  open  into  the  prostatic  portion  of  the 
urethra   by  distinct  orifices,   on  either   side 
Fio.  233.  of  the  median  line.     At  the  same  time,  two 

diverticula  arise  from  the  median  portion  of 
the  vasa  deferentia,  and,  elongating  in  a  back- 
ward direction,  beneath  the  base  of  the  blad- 
der, become  developed  into  sacculated  reser- 
voirs, the  vesiculae  seminales. 

The  left  testicle  is  a  little  later  in  its  de- 
scent than  the  right ;  but  it  passes  farther 
into  the  scrotum,  and,  in  the  adult  condition, 
usually  hangs  lower  than  that  of  the  opposite 
side. 

After  the  testicle  has  passed  into  the  scro- 
tum-  the  se™us  pouch,  which  preceded  its 
descent,  remains  for  a  time  in  communication 

With  the  eeneral  ™vity  of  the  peritoneum. 
In  many  quadrupeds,  as,  for  example,  the 
rabbit,  this  condition  is  permanent ;  and  the 
testicle  may  be  either  drawn  downward  into  the  scrotum,  or  retracted 
into  the  abdomen,  by  the  alternate  action  of  the  gubernaculum  and  the 
cremaster  muscle.  In  the  human  foetus  the  opposite  surfaces  of  the 
peritoneal  pouch  approach  each  other  at  the  inguinal  canal,  forming  a 
constriction,  which  partly  shuts  off  the  testicle  from  the  cavity  of  the 
abdomen.  By  a  continuation  of  this  process,  the  serous  surfaces  come 
in  contact,  and,  adhering  together  at  this  situation  (Fig.  233,  4),  form  a 
kind  of  cicatrix,  by  which  the  cavity  of  the  tunica  vaginalis  (2)  is  shut 
off  from  the  general  cavity  of  the  peritoneum  (3).  The  tunica  vaginalis 


DEVELOPMENT    OF    THE    WO^FFIAN    BODIES,  ETC.       685 

testis  is,  therefore,  originally  a  part  of  the  peritoneum,  from  which  it  is 
subsequently  separated  by  the  constriction  and  adhesion  of  its  opposite 
walls. 

The  separation  of  the  tunica  vaginalis  testis  from  the  peritoneum  is 
usually  complete  in  the  human  foetus  before  birth.  ,But  sometimes  it 
fails  to  take  place  at  the  usual  time,  and  the  intestine  is  then  liable  to 
protrude  into  the  scrotum,  in  front  of  the  spermatic  cord,  giving  rise 
to  congenital  inguinal  hernia.  (Fig.  234.)  The  parts  implicated  in 
this  malformation  have  still  a  tendency  to 
unite ;  and  if  the  intestine  be  retained  by  FIG.  234. 

pressure   within   the   abdomen,  cicatrization  " 
usually  takes  place  at  the  inguinal  canal,  and 
a  cure  is  effected. 

Female  Organs  of  Generation. — At  an 
early  period  of  development  the  ovaries  have 
the  same  external  appearance,  and  occupy  the 
same  position  in  the  abdomen,  as  the  testicles 
in  the  opposite  sex.  The  descent  of  the  ova- 
ries also  takes  place,  to  a  great  extent,  in  the 
same  way  with  that  of  the  testicles.  When, 
in  the  early  part  of  this  descent,  they  reach 
the  lower  edge  of  the  kidneys,  a  cord,  analo- 
gous to  the  gubernaculum  testis,  extends  from  their  lower  extremity, 
downward  and  forward,  to  the  subcutaneous  tissues  at  the  inguinal 
ring.  That  part  of  the  efferent  duct  situated  outside  the  crossing  of 
this  cord  becomes  convoluted,  and  is  converted  into  the  Fallopian  tube; 
while  that  inside  the  same  point  is  developed  into  the  uterus.  The 
upper  portion  of  the  cord  becomes  the  ligament  of  the  ovary ;  its 
lower  portion,  the  round  ligament  of  the  uterus. 

As  the  ovaries  continue  their  descent,  they  pass  below  and  behind 
the  Fallopian  tubes,  which  perform  at  the  same  time  a  movement  of 
rotation,  backward  and  downward ;  the  whole,  together  with  the  liga- 
ments of  the  ovaries  and  the  round  ligaments,  being  enveloped  in 
folds  of  peritoneum,  which  enlarge  with  the  growth  of  the  included 
parts,  and  constitute  finally  the  broad  ligaments  of  the  uterus. 

During  these  changes  in  the  adjacent  organs,  the  two  lateral  halves 
of  the  uterus  fuse  with  each  other  on  the  median  line,  and  become 
covered  with  muscular  fibres.  In  quadrupeds,  the  uterus  remains 
divided  for  the  most  part  into  two  long  conical  tubes  or  cornua  (Fig. 
164).  In  the  human  species,  the  fusion  between  the  lateral  halves  of 
the  organ  is  nearly  complete ;  so  that  the  uterus  presents  externally 
a  rounded,  flattened,  and  somewhat  triangular  figure,  with  the  liga- 
ments of  the  ovary  and  the  round  ligaments  passing  off  from  its  upper 
corners.  Internally,  its  cavity  still  presents  a  strongly  marked  trian- 
gular form,  the  vestige  of  its  original  division. 

Occasionally  the  human  uterus  remains  divided  internally  by  a  ver- 
tical septum.,  running  from  the  middle  of  its  fuudus  toward  the  os 


686  REPRODUCTION. 

internum.  It  may  even  present  a  partial  external  division,  correspond- 
ing with  tin-  situation  of  the  septum,  and  producing  the  malformation 
known  as  utrrux  bicornis,  or  double  uterus. 

The  os  internum  ami  Ofi  externum  are  produced  by  partial  constric- 
tions of  the  original  generative  passage  ;  and  the  distinctions  between 
the  body  of  the  uterus,  the  cervix,  and  the  vagina,  arise  from  the  dif- 
ferent de\  elopment  of  its  mucous  membrane  and  muscular  tunic  in  the 
corresponding  parts.  During  fcetal  life  the  neck  of  the  uterus  <rrows 
fa.Mer  than  its  body ;  so  that  at  birth  the  cervix  uteri  constitutes  nearly 
two-thirds  of  the  entire  or.iran ;  while  the  body  forms  but  little  over 
one-third.  The  cervix,  at  tiiis  time,  is  also  wider  than  the  body;  so 
that  the  whole  organ  presents  a  tapering  form  from  below  upward. 
The  arbor  vita?  uterina  of  the  cervix  is  at  birth  very  fully  developed, 
and  the  mucous  membrane  of  the  body  is  thrown  into  three  or  four 
folds  which  radiate  upward  from  the  os  internum.  The  cavity  of  the 
cervix  is  filled  with  transparent  semi-solid  mucus. 

The  position  of  the  uterus  at  birth  is  different  from  that  in  adult 
life;  nearly  the  entire  organ  being  above  the  symphysis  pubis,  and  its 
inferior  extremity  passing  below  that  level  only  by  about  six  milli- 
metres. It  is  also  slightly  anteflexed  at  the  junction  of  the  body  and 
cervix.  After  birth,  the  uterus  with  its  appendages  continues  to  de- 
scend; and  at  puberty  its  fundus  is  just  below  the  level  of  the  sym- 
physis pubis. 

The  ovaries  at  birth  are  narrow  and  elongated  in  form.  They  con- 
tain an  abundance  of  eggs ;  each  enclosed  in  a  Graafian  follicle,  and 
averaging  .04  millimetre  in  diameter.  The  vitellus  in  most  is  im- 
perfectly formed,  and  in  some  is  hardly  distinguishable.  The  Graafian 
follicle  at  this  period  contains  no  fluid,  but  only  the  egg  and  the  layer 
of  cells  forming  the  "membrana  granulosa."  Inside  this  layer  is  to 
be  seen  the  germinative  vesicle,  with  the  germinative  spot,  surrounded 
by  a  faintly  granular  vitellus,  more  or  less  abundant  in  different  parts 
of  the  ovary.  Some  of  the  Graafian  follicles  containing  eggs  are  as 
large  as  .05  millimetre;  others  as  small  as  .02  millimetre.  In  the  very 
smallest  the  cells  of  the  membrana  granulosa  appear  to  fill  the  cavity 
of  the  follicle,  concealing  the  rudiments  of  the  primitive  egg. 


CHAPTER  XVI. 
DEVELOPMENT  OF  THE  VASCULAR  SYSTEM. 

THE  vascular  system  presents  itself,  during  different  periods  of  life, 
under  three  distinct  forms,  which  follow  each  other  in  the  progress 
of  development,  as  different  organs  are  employed  in  the  functions  of 
nutrition.  The  first  form  is  that  of  the  vitelline  circulation,  which 
exists  at  a  period  when  the  vitellus  is  the  source  of  nutrition  for  the 
embryo.  The  second  is  the  placental  circulation,  in  which  the  mate- 
rials of  nourishment  are  supplied  by  the  placenta,  and  which  lasts 
through  the  greater  part  of  foetal  life.  The  third  is  the  adult  circu- 
lation, in  which  nutrition  and  the  renovation  of  the  blood  are  provided 
for  by  the  lungs  and  the  intestinal  canal. 

Vitelline  Circulation. — When  the  body  of  the  embryo  has  begun  to 
be  formed  in  the  centre  of  tho  blastoderm,  a  number  of  blood-vessels 
shoot  out  from  its  sides  and  ramify  over  the  neigh- 
boring parts  of  the  vitelline  sac,  forming  by  their  Fio-^235. 
inosculation  the  plexus  of  the  area  vasculosa.  In  the 
egg  of  the  fish  (Fig.  235),  the  area  vasculosa  occupies 
the  whole  surface  of  the  vitellus,  outside  the  body 
of  the  embryo.  A  number  of  arteries  pass  out  from 
each  side,  supplying  the  vascular  network ;  and  the 
blood  is  returned  to  the  embryo  by  an  anterior  vitel- 
line vein,  passing  upward  along  the  front  of  the  egg,  Ec;G  °?  FJSH.  (Jar/1a' 

&  bacca),  showing   the 

and  entering  the  body  beneath  the  head.  vitelline  circulation. 

In  the  egg  of  the  fowl  (page  636),  the  area  vascu- 
losa spreads  gradually  over  the  vitelline  sac  from  within  outward. 
During  this  extension  some  of  its  vessels  change  in  relative  size  and 
importance.  The  vena  terminalis,  forming  its  outer  border,  becomes 
less  distinct ;  and,  in  addition  to  the  anterior  and  lateral  vitelline  veins, 
in  front  and  on  the  sides,  there  is  also  a  "posterior  vitelline  vein," 
coming  from  the  hinder  part  of  the  area  vasculosa  and  reaching  the 
embryo  beneath  its  caudal  extremity. 

In  man  and  mammalians,  the  first  formation  of  the  area  vasculosa  is 
similar  to  that  in  fishes  and  birds.  But  owing  to  the  small  size  and 
rapid  exhaustion  of  the  vitellus  as  a  source  of  nourishment,  this  form 
of  the  circulation  never  acquires  a  high  degree  of  development,  and 
soon  becomes  retrograde.  It  presents,  however,  certain  modifications, 
connected  with  the  origin  of  various  parts  of  the  permanent  vascular 
system. 

These  modifications  relate  mainly  to  the  vessels  distributing  the 

687 


REPRODUCTION. 


FIG.  236. 


blood  to  the  external  vascular  plexus,  and  returning  it  thence  to  the 
embryo.  As  the  embryo  and  the  entire  egg  increase  in  size,  two  arte- 
ries and  two  veins  become  larger  than  the  rest,  and  subsequently  do 
the  whole  work  of  conveying  the  blood  to  and  from  the  area  vasculosa. 
The  arteries  emerge  from  the  lateral  edges  of  the  embryo,  on  the 
ri-lit  and  left  sides;  while  the  veins  re-enter  at  about  the  same  point 
and  nearly  parallel  with  them.  These  four  vessels  are  termed  the 
omphalo-mesenteric  arteries  and  veins. 

The  arrangement  of  the  circulatory  apparatus  in  the  interior  of  the 
body  at  this  time  is  as  follows :  The  heart  is  situated  at  the  median 
line,  immediately  beneath  the  head,  and  in  front  of  the  oesophagus.  It 
receives  at  its  lower  extremity  the  united  trunks  of  the  two  omphalo- 
mesenteric  veins,  and  at  its  upper  extremity  gives  off  two  vessels  which 
almost  immediately  divide  into  two  sets  of  lateral  arches,  bending  back- 
ward along  the  sides  of  the  neck,  and  reuniting  into  two  trunks  in  front 
of  the  vertebral  column.  These  trunks  then  run  from  above  downward 

on  each  side  the  median  line.  They 
are  called  the  vertebral  arteries,  on 
account  of  their  situation,  adjacent 
to  and  parallel  with  the  vertebral 
column.  They  give  off,  throughout 
their  course,  small  lateral  branches, 
which  supply  the  body  of  the  embryo, 
and  also  two  larger  branches — the 
omphalo-mesenteric  arteries — which 
pass  out,  as  above  described,  to  the 
area  vasculosa.  The  two  vertebral 
arteries  remain  separate  in  the  upper 
part  of  the  body,  but  fuse  with  each 
other  a  little  below  the  level  of  the 
heart;  so  that,  beyond  this  point, 
there  remains  but  one  large  artery — 
the  aorta  —  running  from  above 
downward  along  the  median  line, 
giving  off  the  omphalo-mesenteric 

arteries  to  the  area  vasculosa,  and  supplying  smaller  branches  to  the 
body,  the  walls  of  the  intestine,  and  the  other  organs  of  the  embryo. 

This  is  the  condition  which  marks  the  first  or  vitelline  circulation. 
A  change  now  begins  to  take  place,  in  which  the  vitellus  is  superseded, 
as  an  organ  of  nutrition,  by  the  placenta ;  giving  rise  to  the  second  or 
placental  circulation. 

riin-rnfal  Circulation. — After  the  umbilical  vesicle  has  been  formed 
by  the  process  already  described  (page  630),  a  part  of  the  vitellus 
remains  included  in  it.  while  the  rest  is  retained  in  the  abdomen, 
enclosed  in  the  intestinal  muni.  As  these  two  organs  (umbilical  vesicle 
:iml  intestine)  are  originally  parts  of  the  same  vitelline  sac,  they  remain 
-ni>:, lied  by  the  same  vascular  system,  namely,  the  omphulo-mesenteric 


Diagram  of  the  EMBRYO  AND  ITS  VK881  i  -. 
showing  the  circulation  of  the  umbilical  vesi- 
cle ;  and  also  that  of  the  allantois,  beginning 
to  be  formed. 


DEVELOPMENT    OF    THE    VASCULAR    SYSTEM.       689 

vessels.  Those  within  the  abdomen  supply  the  mesentery  and  intestine  ; 
while  the  remainder  pass  outward  and  ramify  on  the  walls  of  the  um- 
bilical vesicle  (Fig.  236).  At  first  there  are,  as  above  mentioned,  two 
omphalo-mesenteric  arteries  emerging  from  the  body,  and  two  omphalo- 
mesenteric  veins  returning  to  it ;  but  afterward  the  two  arteries  are 
replaced  by  a  common  trunk,  while  a  similar  change  takes  place  in 
the  veins.  Subsequently,  therefore,  there  remain  but  one  artery  and 
one  vein,  connecting  the  internal  and  external  portions  of  the  vitelline 
circulation. 

The  vessels  belonging  to  this  system  are  called  the  omphalo-mesen- 
teric vessels,  because  a  part  of  them  (omphalic  vessels)  pass  outward, 
by  the  umbilicus,  or  "  omphalos,"  to  the  umbilical  vesicle,  while  the 

FIG.  237. 


Diagram  of  the  EMBRYO  AND  ITS  VESSELS,  showing  the  second  or  placental  circulation.  The  intes- 
tine has  become  further  developed,  and  the  mesenteric  arteries  have  enlarged,  while  the  umbili- 
cal vesicle  and  its  vascular  branches  are  reduced  in  size.  The  large  umbilical  arteries  are  seen 
passing  out  to  the  placenta. 

remainder  (mesenteric  vessels)  ramify  upon  the   mesentery  and   the 
intestine. 

At  first,  the  circulation  of  the  umbilical  vesicle  is  more  important 
than  that  of  the  intestine ;  and  the  omphalic  artery  and  vein  appeal- 
accordingly  as  large  trunks,  of  which  the  mesenteric  vessels  are  small 
branches  (Fig.  236).  Afterward  the  intestine  enlarges,  while  the  um- 
bilical vesicle  diminishes,  and  the  proportion  between  the  two  sets  of 
vessels  is  reversed.  The  mesenteric  vessels  then  come  to  be  the  prin- 
cipal trunks,  while  the  omphalic  vessels  are  minute  branches,  running 

2T 


690  REPRODUCTION. 

out  to  the  umbilici!  1  vesicle,  and  ramifying  in  a  few  scanty  twigs  upon 
its  surface  (Fig.  23  T). 

In  the  meantime,  the  allantois  is  formed  by  a  protrusion  from  the 
lower  extremity  of  the  intestine,  which,  carrying  with  it  two  arteries 
and  two  veins,  passes  out  from  the  abdomen,  and  comes  in  contact 
wiili  the  external  membrane  of  the  egg.  The  arteries  of  the  allantois, 
termed  the  umbilical  arteries,  are  supplied  by  branches  of  the  abdom- 
inal aorta;  while  the  venous  trunks  returning  from  it,  or  the  umbilical 
reins,  join  the  mesenteric  veins,  and  empty  with  them  into  the  venous 
extremity  of  the  heart.  As  the  umbilical  vesicle  diminishes,  the  allan- 
tois enlarges ;  and  the  latter  is  converted,  in  the  human  subject,  into 
a  vascular  chorion,  which  serves  for  the  formation  of  the  placenta 
(Fig.  237).  As  the  placenta  soon  becomes  the  only  source  of  nutrition 
for  the  fetus,  its  vessels  increase  in  size,  and  preponderate  over  all 
other  parts  of  the  circulatory  system.  During  the  early  periods  of  its 
formation  there  are,  as  above  mentioned,  two  umbilical  arteries  and 
two  umbilical  veins.  Subsequently  one  of  the  veins  disappears,  while 
the  other  becomes  enlarged  in  proportion,  and  returns  the  whole  of  the 
blood  from  the  placenta  to  the  foetus.  For  a  long  time  previous  to 
birth  the  umbilical  cord  contains  therefore  two  umbilical  arteries,  and 
but  one  umbilical  vein. 

Adult  Circulation. — The  placental  circulation  is  exchanged  at  birth 
for  the  third  or  adult  circulation.  This  is  distinguished  by  the  disap- 
pearance of  the  placenta  and  the  vessels  connected  with  it,  and  by  the 
entrance  into  activity  of  the  lungs  and  the  alimentary  canal,  as  the 
organs  of  nutrition  and  aeration.  A  large  proportion  of  the  blood  is 
accordingly  turned  away  from  its  former  channels,  and  distributed  to 
new  organs.  This  change  is  comparatively  rapid.  The  previous  tran- 
sition, from  the  vitelline  to  the  placental  circulation,  was  gradual ;  the 
umbilical  vesicle  diminishing  simultaneously  with  the  enlargement  of 
the  placenta,  and  the  two  organs,  with  their  blood-vessels,  coexisting 
for  a  certain  period.  But  at  birth  the  placenta  is  suddenly  withdrawn 
from  the  circulatory  system  and  replaced  in  functional  activity  by  the 
lungs  and  the  alimentary  canal. 

This  change,  however,  has  been  already  provided  for  by  the  gradual 
development  of  the  necessary  organs,  and  by  corresponding  alterations 
in  both  the  arterial  and  venous  systems. 

Development  of  the  Arterial  System. — At  an  early  period  of  devel- 
opment, the  arterial  trunks,  after  passing  off  from  the  anterior  extremity 
of  the  heart,  curve  backward,  as  already  described  (page  688).  in  two 
sets  of  lateral  branehes,  toward  the  vertebral  column,  after  which  they 
reunite,  to  form  the  "vertebral  arteries."  The  curved  branches,  em- 
liraeiiiL:-  the  sides  of  the  neck,  are  called  the  cervical  arches.  They 
pa—  through  the  substance  of  t he  "  visceral  folds,"  already  described 
(paire  r,7T).  and  are  separated  from  each  other  by  the  intervening  cer- 
vical fissures.  In  ihe  embryo  chick,  according  to  Foster  and  Balfour, 
three  cervical  arches,  in  the  three  upper  visceral  folds,  have  been  formed 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM.   691 

by  the  end  of  the  second  day  of  incubation.  During  the  third  and 
fourth  days,  the  first  and  second  cervical  arches  become  obliterated, 
a  fourth  and  a  fifth  appearing  at  the  same  time,  in  the  corresponding 
visceral  folds.  Thus  there  are,  in  all,  five  vascular  cervical  arches; 
but  only  three  are  to  be  found  coexisting  at  any  one  time. 

In  fishes,  the  cervical  arches  remain  as  permanent  blood-vessels  sup- 
plying the  gills,  four  or  five,  in  number  on  each  side.  In  birds  and 
mammalians,  some  of  the  cervical  arches  disappear,  or  leave  only  cer- 
tain arterial  inosculations  as  vestiges  of  their  embryonic  existence. 
Some,  on  the  other  hand,  remain  as  permanent  vascular  trunks  or 
branches,  forming  important  parts  of  the  adult  arterial  system. 

The  details  of  growth  and  modification  in  the  cervical  arches  are  not 
all  described  in  the  same  manner  by  different  observers;  and  there 
seems  to  be  some  difference,  in  this  respect,  between  mammalians  and 
birds.  The  general  features  of  the  process,  however,  are  as  follows : 

The  two  ascending  trunks,  on  the  anterior  part  of  the  neck,  from 
which  the  cervical  arches  are  given  off,  become  the  carotid  arteries. 
The  first  and  second,  that  is,  the  two  upper  cervical  arches,  on  each 
side,  disappear  completely,  or  *remain  only  as  small  and  inconstant  arte- 
rial inosculations.  The  third  arch  becomes  the  subclavian  artery,  giv- 
ing off  the  permanent  vertebral  artery,  and  continuing  its  course  as 
the  axillary  artery,  to  the  upper  limb.  The  fourth  cervical  arch 
undergoes  different  changes  on  the  two  sides.  On  the  left  side  it 
becomes  enormously  enlarged,  giving  off,  as  secondary  branches,  all- the 
arterial  trunks  going  to  the  head  and  upper  limbs,  and  is  thus  converted 
into  the  arch  of  the  aorta.  On  the  right  side  it  grows  smaller,  and 
ultimately  disappears ;  so  that  at  last  there  is  only  a  single  aortic  arch, 
situated  on  the  left  of  the  median  line,  and  continuous  below  with  the 
thoracic  aorta. 

The  fifth  or  last  cervical  arch  becomes  on  each  side  the  pulmonary 
artery ;  its  external  portion  on  the  right  side  disappearing  at  a  very 
early  period,  but  on  the  left  remaining  for  a  certain  time,  as  the  ductus 
arteriosus,  between  the  pulmonary  artery  and  the  aorta. 

Notwithstanding  that  all  the  cervical  arches  are  at  first,  as  their 
name  implies,  situated  in  the  region  of  the  neck,  their  remains  or  per- 
manent representatives  in  the  complete  form  of  the  arterial  system, 
come  to  be  placed  farther  downward,  and  even  in  the  cavity  of  the 
chest.  This  is  due  to  the  varying  rapidity  of  growth  in  different  parts, 
at  successive  periods  of  development.  The  thorax  at  first  has  no  exist- 
ence as  a  distinct  portion  of  the  trunk ;  the  heart  being  placed  imme- 
diately beneath  the  head,  and  afterward  changing  its  position  with  the 
increasing  development  of  the  lungs  and  chest.  The  neck,  with  the 
ffisophagus  and  trachea,  also  elongates  in  an  upward  direction,  so  that 
the  vascular  organs  of  this  region  afterward  occupy  a  situation  farther 
down.  In  fishes,  where  there  are  no  lungs  and  no  thoracic  cavity,  the 
cervical  arches  are  permanent,  and  the  heart  remains  in  the  anterior 
portion  of  the  trunk,  just  behind  the  gills. 


()i'-2  REPRODUCTION. 

Corresponding  changes  take  place,  during  this  time,  in  the  lower  part 
of  the  body.  Here  the  abdominal  aorta  runs  undivided,  on  the  median 
line,  to  the  end  of  the  spinal  column  ;  giving  off  lateral  branches  to  the 
intestine  and  the  abdominal  walls.  When  the  allantois  is  developed, 
two  of  these  branches  accompany  it,  and  become,  consequently,  the 
umbilical  arteries.  These  vessels  increase  so  rapidly  in  size,  that  they 
soon  appear  as  main  divisions  of  the  aorta  ;  while  its  original  continua- 
tion, running  to  the  end  of  the  spinal  column,  appears  as  a  small  branch 
given  off  at  the  point  of  bifurcation.  The  lower  limbs  are  supplied  by 
two  small  branches  from  the  umbilical  arteries  near  their  origin. 

Up  to  this  time,  the  pelvis  and  lower  limbs  are  but  slightly  developed. 
Subsequently  they  grow  more  rapidly,  in  proportion  to  the  rest  of  the 
body,  and  their  arteries  enlarge,  to  a  corresponding  degree.  That  por- 
tion of  the  umbilical  arteries  lying  between  the  bifurcation  of  the  aorta 
and  the  branches  going  to  the  lower  limbs,  becomes  the  common  iliac 
arteries,  which  afterward  divide  into  the  umbilical  arteries  proper  and 
the  femorals.  Subsequently,  in  accordance  with  the  growth  of  the 
pelvis  and  lower  limbs,  the  relative  size  of  their  blood-vessels  is  still 
further  increased ;  and  at  last  the  arterial  system  in  this  part  of  the 
body  assumes  the  arrangement  belonging  to  the  latter  periods  of  ges- 
tation. The  aorta  divides,  as  before,  into  the  two  common  iliac  arteries. 
These  divide  into  the  external  iliacs,  supplying  the  lower  limbs,  and  the 
internal  iliacs,  supplying  the  pelvis ;  and  this  division  is  so  placed  that 
the  umbilical  arteries  arise  from  the  internal  iliacs,  of  which  they  now 
appear  to  be  secondary  branches. 

After  birth,  the  umbilical  arteries  become  for  the  most  part  atro- 
phied, and  are  converted,  in  the  adult  condition,  into  solid  cords,  run- 
ning upward  to  the  umbilicus.  Their  lower  portions,  however,  remain 
pervious,  under  the  name  of  the  "  hypogastric  arteries,"  and  give  off 
branches  supplying  the  urinary  bladder.  The  terminal  continuation 
of  the  original  abdominal  aorta  is  the  arteria  sacra  media,  which,  in 
the  adult,  runs  downward  on  the  anterior  surface  of  the  sacrum,  sup- 
plying the  rectum  and  the  anterior  sacral  nerves. 

Development  of  the  Venous  System. — According  to  Coste,  the  prin- 
cipal veins  of  the  body  consist  at  first  of  two  long  venous  trunks,  the 
vertebral  veins  (Fig.  238),  running  along  the  sides  of  the  vertebral 
column,  parallel  with  the  vertebral  arteries.  They  receive  in  succession 
all  the  intercostal  veins,  and  empty  into  the  heart  by  two  lateral  trunks, 
the  canals  of  Guvier.  When  the  lower  limbs  become  developed,  their 
two  veins  join  the  vertebral  veins  in  the  posterior  portion  of  the  body; 
and,  crossing  them,  afterward  unite  with  each  other,  constituting  a 
third  vein  of  ne\v  formation  (Fig.  239,  a),  which  runs  upward  a  little 
to  the  right  of  the  median  line,  and  empties  by  itself  into  the  lower 
extremity  of  the  heart. 

The  two  branches  which  thus  unite  become  afterward  the  common 
iliac  veins;  and  the  trunk  resulting  from  their  union  is  the  vena  cava 
inferior.  Subsequently,  the  vena  cava  inferior  becomes  very  much 


DEVELOPMENT    OF    THE    VASCULAR    SYSTEM.       693 

larger  than  the  vertebral  veins,  and  returns  to  the  heart  nearly  all  the 
blood  from  the  lower  half  of  the  body. 

Above  the  level  of  the  heart  the  vertebral  and  intercostal  veins  retain 
their  relative  size  until  the  development  of  the  upper  limbs  has  com- 
menced. Then  two  of  the  intercostal  veins  increase  in  diameter  (Fig. 
240),  and  become  the  right  and  left  subclavians ;  while  the  vertebral 


FIG.  238. 


FIG.  239. 


FIG.  240. 


Diagram  of  the  VENOUS 
SYSTEM  in  its  early  con- 
dition ;  showing  the  ver- 
tebral veins  emptying 
into  the  heart  by  two 
lateral  trunks,  the  "ca- 
nals of  Cuvier." 


VENOUS  SYSTEM  farther  ad- 
vanced, showing  the  iliac 
and  subclavian  veins.  —  a. 
Vein  of  new  formation, 
which  becomes  the  inferior 
vena  cava.  6.  Transverse 
branch  of  new  formation, 
which  becomes  the  left  vena 
innominata. 


Further  development  of  the 
VENOUS  SYSTEM. — The  ver- 
tebral veins  are  reduced  in 
size,  and  the  canal  of  Cuvier, 
on  the  left  side,  is  disappear- 
ing, c.  Transverse  branch 
of  new  formation,  which 
becomes  the  vena  azygos 
minor. 


veins  situated  above  them  become  the  right  and  left  jugular  veins. 
Just  below  the  junction  of  the  jugulars  with  the  subclavians,  a  small 
branch  of  communication  now  appears  between  the  two  vertebrals 
(Fig.  239,  b),  passing  from  left  to  right,  and  emptying  into  the  right 
vertebral  vein  a  little  above  the  heart ;  so  that  a  part  of  the  blood 
coming  from  the  left  side  of  the  head,  and  the  left  upper  limb,  still 
passes  down  the  left  vertebral  vein  to  the  heart  on  its  own  side,  while 
a  part  crosses  over  by  the  communicating  branch  (b),  and  reaches  the 
heart  through  the  right  vertebral  vein.  Soon  afterward,  this  branch 
of  communication  enlarges  so  rapidly  that  it  preponderates  over  the 
vertebral  vein  from  which  it  originated  (Fig.  240),  and  becomes  the 
left  vena  innominata. 

On  the  left  side,  that  portion  of  the  superior  vertebral  vein,  which 
is  below  the  subclavian,  remains  as  a  branch  of  the  vena  innominata, 
receiving  the  six  or  seven  upper  intercostal  veins ;  while  on  the  right 
side  it  becomes  excessively  enlarged,  receiving  the  blood  of  both 


694 


R  E  P  R  O  D  U  C  T  J  ( >  \  . 


FIG.  241. 


juirular  and  both  subclavian  veins,  and  is  converted   into  the  vena 
cava  superior. 

The  left  cnnal  of  Cuvier,  by  which  the  left  vertebral  vein  at  first 
communicates  with  the  heart,  is  subsequently  obliterated,  while  that 
on  the  right  side  becomes  excessively  enlarged,  forming  the  lower 
extremity  of  the  vena  cava  superior. 

The  superior  and  inferior  venae  cavas,  accordingly,  do  not  correspond 
with  each  other  so  far  as  regards  their  origin.  The  superior  vena 
cava  is  one  of  the  original  vertebral  veins ;  while  the  inferior  vena 
cava  is  a  vessel  of  new  formation,  resulting  from  the  union  of  two 
lateral  trunks  from  the  inferior  limbs. 

The  remaining  vertebral  veins  finally  assume  the  condition  shown 
in  Fig.  241,  which  is  the  adult  form  of  the  venous  circulation.     At 
the  lower  part  of  the  abdomen  the  vertebral  veins  send  inward  trans- 
verse branches  of  communication  to  the  vena 
cava  inferior,  between  the  points  at  which  they 
receive  the  intercostal  veins.     These  branches 
of  communication  become  the  lumbar  veins  (7), 
which  in  the  adult  communicate  with  each  other 
by  arched  branches,  a  short  distance  to  the  side 
of  the  vena  cava.     Above  the  level  of  the  lum- 
bar arches,  the  vertebral  veins  retain  their  origi- 
nal direction.     That  upon  the  right  side  still 
receives  all  the  right  intercostal  veins,  and  be- 
comes the  vena  azygos  major  (8).   It  also  receives 
from  its  fellow  of  the  left  side  a  small  branch  of 
communication  (Fig.  240,  c),  which  soon  enlarges 
to  such  an  extent  as  to  bring  over  to  the  vena 
azygos  major  all  the  blood  of  the  five  or  six 
lower  intercostal  veins  of  the  left  side,  becom- 
ing, in  this  way,  the  vena  azygos  minor  (Fig. 
241,  9).      The   six   or   seven  upper   intercostal 
veins  on  the  left  side  still  empty,  as  before,  into 
their  own  vertebral  vein  (,0),  which,  joining  the 
AtoV0SYSTKM.-itbRiIht  left  vena  innominata  above,  is  known  as  the 
anricir  of   HI.    h.-sirt.  2.  superior  intercostal  vein.     The  left   canal  of 
JvJpdartitiirvLtetelih   Cuvier  ^as  by  this  time  disappeared;  so  that 
reins.   B,  v.-na  cm  all  the  venous  blood  now  enters  the  heart  by 

inferior.    6,  G.   Iliac   veins.       ,  .  ,       .         .  . 

7.  i.umia,   v,  ins.  s.  \vna  tne  superior  and  the  inferior  vena  cava.     But 
azygos  major.  9.  \ ,  n;.  a/y-   the  original  vertebral  veins  are  still  continuous 

gos  minor.    10.  Superior  in-    ,,  ,, 

throughout,  though  much  diminished  in  size  at 


certain  points;  since  both  the  un-ator  and  lesser 

azygous  veins  inosculate  below  \viththe  superior  lumbar  veins,  and 
tin-  .-upei-ior  intercostal  vein  inosculates  In-low  with  the  lesser  azygous 
vein,  he  fore  it  crosses  to  the  right  side. 

There  ;uv  two  parts  of  the  circulatory  apparatus,  the  development 
of  which   i.-  Miiliek-ntly  important  to   be  described  .-eparately.     These 


DEVELOPMENT    OF    THE    VASCULAR    SYSTEM.        695 


FIG.  242. 


CIRCULATION.  —  1.  Omphalo- 
mesenteric  vein.  2.  Hepatic 
vein.  3.  Heart.  The  dotted 
line  shows  the  situation  of 
the  future  umbilical  vein. 


are,  first,  the  liver  and  the  ductus  venosus,  and  secondly,  the  heart 
and  ductus  arteriosus. 

The  Hepatic  Circulation  and  Ductus  Venosus.— The  liver  appears 
at  a  very  early  period,  in  the  upper  part  of  the  abdomen,  as  a  mass  of 
glandular  and  vascular  tissue,  developed  around 
the  upper  portion  of  the  omphalo-mesenteric 
vein,  just  below  its  termination  in  the  heart 
(Fig.  242).  As  soon  as  the  organ  has  attained 
a  considerable  size,  the  omphalo-mesenteric 
vein  (t)  breaks  up  in  its  interior  into  a  capil- 
lary plexus,  the  vessels  of  which  reunite  into 
a  venous  trunk,  conveying  the  blood  toward 
the  heart.  The  omphalo-mesenteric  vein  below 
the  liver  then  becomes  the  portal  vein  ;  while 

above  that  organ  it  receives  the  name  of  the  Earlv  form  of  the  HEPATIC 
hepatic  vein  (2).     The  liver,  accordingly,  is  at 
this  time  supplied  with  blood  entirely  by  the 
portal  vein,  coming  from  the  umbilical  vesicle 
and  the  intestine  ;  and  all  the  blood  derived 

from  this  source  passes  through  the  hepatic  circulation  before  reaching 
the  heart. 

But  soon  afterward  the  allantois  makes  its  appearance,  and  becomes 
developed  into  the  placenta ;  and  the  umbilical  vein  returning  from  it 
joins  the  omphalo-mesenteric  vein,  and  takes 
part  in  the  formation  of  the  hepatic  capillary 
plexus.     Since  the  umbilical  vesicle,  however, 
becomes  atrophied  and  the  intestine  remains 
inactive,  while  the  placenta  increases  in  size 
and  importance,  a  period  arrives  when  the  liver 
receives  more  blood  by  the  umbilical  vein  than 
by  the  portal  vein  (Fig.  243).     The  umbilical 
vein  then  passes  into  the  liver  at  the  longitu- 
dinal fissure,  and  ramifies  throughout  the  left 
lobe  of  the  organ.    To  the  right  it  sends  a  large  HEPATIC  CIRCULATION  farther 
branch  of  communication,  which  opens  into  the     advanced.— i.  Portal  vein.  2. 

,    i          •  T  ,.   •,-,  •  -i        r»       .  i         •          Umbilical  vein.     3.  Hepatic 

portal  vein,  and  partially  provides  for  the  cir-     vein 

culation  in  the  right  lobe.     The  liver  is  thus 

supplied  with  blood  from  two  sources,  the  most  abundant  of  which  is 

the  umbilical  vein ;  while  all  the  blood  which  enters  it  circulates,  as 

before,  through  its  capillary  vessels. 

But  the  liver  at  this  time  is  much  larger,  in  proportion  to  the  other 
organs,  than  at  a  later  period.  In  the  fostal  pig,  when  very  young,  it 
amounts  to  nearly  twelve  per  cent,  of  the  whole  body ;  while  before 
birth  it  diminishes  to  seven,  six,  and  even  three  or  four  per  cent.  In 
the  latter  part  of  foetal  life,  therefore,  its  capillary  circulation  becomes 
insufficient  to  accommodate  all  the  blood  returning  from  the  placenta ; 
and  a  vascular  canal  is  formed  in  its  interior,  by  which  a  portion  of  the 


FIG.  243. 


696 


REPRODUCTION. 


placental  blood  reaches  the  heart  without  passing  through  the  hepatic 
capillaries.     This  canal  is  the  Ductus  venosus. 

The  ductus  venosus  is  formed  by  a  dilatation  of  one  of  the  hepatic 
capillaries  (Fig.  244),  which  is  thus  converted  into  a  wide  branch  of 
communication  between  the  umbilical  vein  below  and  the  hepatic  vein 
above.  The  circulation  in  the  liver,  at  this  period,  is  as  follows:  A 
cerhlin  quantity  of  venous  blood  still  enters  through  the  portal  vein  (t), 
and  circulates  in  a  part  of  the  capillary  system  of  the  right  lobe.  The 
umbilical  vein  (2)  enters  the  liver  a  little  to  the  left,  bringing  a  larger 
quantity  of  blood,  which  divides  into  three  principal  streams.  One  of 


FIG.  244. 


FIG.  245. 


HEPATIC  CIRCULATION  during  the  latter 
part  of  foetal  life.— 1.  Portal  vein.  2.  Um- 
bilical vein.  3.  Left  branch  of  umbil- 
ical vein.  4.  Right  branch  of  umbilical 
vein.  5.  Ductus  venosus.  6.  Hepatic 
vein. 


ADULT  FORM  OF  HEPATIC  CIRCULATION.— 
1.  Portal  vein.  2.  Obliterated  umbilical 
vein,  forming  the  round  ligament ;  the 
continuation  of  the  dotted  lines  through 
the  liver  shows  the  situation  of  the  ob- 
literated ductus  venosus.  3.  Hepatic  vein. 
4.  Left  branch  of  portal  vein. 


them  passes  through  the  left  branch  of  the  umbilical  vein  (3)  into  the 
capillaries  of  the  left  lobe ;  another  turns  off  through  the  right  branch 
(<),  and,  joining  the  blood  of  the  portal  vein,  circulates  through  the 
capillaries  of  the  right  lobe ;  while  the  third  passes  through  the  ductus 
venosus  (5)  to  the  hepatic  vein  without  traversing  any  part  of  the 
capillary  plexus. 

This  form  of  the  hepatic  circulation  continues  until  birth.  At  that 
time,  two  important  changes  take  place.  First,  the  placental  circula- 
tion is  cut  off ;  and  secondly,  a  much  larger  quantity  of  blood  than 
before  is  supplied  to  the  lungs  and  the  intestine.  The  superabundant 
blood,  previously  circulating  in  the  placenta,  is  now  diverted  to  the 
lung's;  while  the  intestinal  canal  becomes  the  only  source  of  venous 
>iipply  for  the  hepntic  blood.  The  following  changes,  therefore,  take 
place  in  the  liver  (Fig.  24f>).  First,  the  umbilical  vein  shrivels  and 
become-  impervious.  It  remains  in  this  condition,  in  the  adult,  as  the 
rnuml  HijiuiH'nt  ( ..).  extending  from  the  inner  surface  of  the  abdominal 
walk  at  the  umbilicus,  to  the  longitudinal  fissure  of  the  liver.  Secondlv, 


DEVELOPMENT    OF    THE    VASCULAR    SYSTEM.        697 


the  ductus  venosus  is  also  obliterated.  Thirdly,  the  blood  entering  the 
liver  by  the  portal  vein  (t)  passes  by  its  right  branch,  as  before,  to  the 
right  lobe.  But  in  its  left  branch  (4)  the  course  of  the  blood  is  reversed. 
This  was  formerly  the  right  branch  of  the  umbilical  vein,  its  blood 
passing  from  left  to  right.  It  now  becomes  the  left  branch  of  the 
portal  vein ;  and  its  blood  passes  from  right  to  left,  for  distribution  to 
the  capillary  vessels  of  the  left  lobe. 

According  to  Guy,  the  umbilical  vein,  in  man,  is  completely  closed 
at  the  end  of  the  fifth  day  after  birth. 

The  Heart,  and  Ductus  Arteriosus. — When  the  embryonic  circulation 
is  first  established,  the  heart  is  a  straight  tubular  canal  (Fig.  246), 
receiving  the  veins  at  its  lower  extremity  and  giving  off  an  arterial 


FIG.  246. 


FIG.  247. 


FIG.  248. 


Earliest  form  of  the 
FCETAL  HEART.  —  1. 
Venous  extremity.  2. 
Arterial  extremity. 


<\ 


FCETAI,  HEART,  bent 
upon  itself. — 1.  Ven- 
ous extremity.  2.  Ar- 
terial extremity. 


FCETAL  HEART  still  farther  de- 
veloped.—1.  Aorta.  2.  Pul- 
monary artery.  3,  3.  Pul- 
monary branches.  4.  Ductus 
arteriosus. 


trunk  at  its  upper  extremity.  It  soon  afterward  becomes  bent  in  a 
sharp  curve  (Fig.  241),  which  brings  its  venous  and  arterial  extremities 
nearer  the  same  level ;  but  in  such  a  way  that  its  venous  portion  is 
situated  behind,  and  its  arterial  portion  in  front.  It  has  still  a  single, 
undivided  cavity ;  and  the  blood  passes  through  it  in  a  continuous 
stream,  turning  upon  itself  at  the  point  of  curvature  and  emerging  by 
the  arterial  orifice. 

Subsequently  the  venous  extremity  of  the  heart  shows  a  longitudinal 
furrow  which  divides  its  originally  single  cavity  into  two  secondary 
compartments,  placed  side  by  side.  These  compartments  become  the 
right  and  left  auricles ;  and  they  are  furthermore  separated,  by  trans- 
verse constrictions,  from  the  curved  portion  of  the  heart,  which  is  to 
form  the  ventricles.  The  cavities  of  the  two  ventricles  become  sepa- 
rated from  each  other  by  the  growth  of  a  septum,  which  begins  at  the 
most  prominent  part  of  the  curvature  or  apex  of  the  organ,  and  gradu- 
ually  extends  toward  its  base.  When  the  interventricular  septum  is 
completely  formed,  its  situation  is  indicated  by  a  corresponding  furrow 
on  the  external  surface  of  the  organ. 

The  primitive  arterial  trunk,  springing  from  the  upper  extremity  of 
the  heart,  has  already  been  divided,  by  a  longitudinal  furrow,  into  two 
secondary  trunks,  lying  side  by  side  and  nearly  parallel  with  each  other 


698  REPRODUCTION. 

(Fig.  248).  One  of  these  secondary  trunks  becomes  the  commencement 
of  the  aorta,  the  other  the  pulmonary  artery ;  and  the  relation  of  the 
furrow  between  them  to  the  interventricular  septum  is  such  that  the 
aorta  communicates  with  the  left  ventricle,  and  the  pulmonary  artery 
with  the  right. 

But  the  pulmonary  artery,  beside  supplying  small  branches  on  each 
side  to  the  lungs,  also  furnishes  a  large  branch  of  communication  to  the 
arch  of  the  aorta  beyond.  This  branch  is  so  voluminous  that  it  appears 
to  be  the  main  continuation  of  the  pulmonary  trunk.  It  forms,  accord- 
ingly, an  open  canal  or  duct  between  the  two  principal  arteries  nearest 
the  heart,  and  is  known  by  the  name  of  the  Ductus  arteriosus. 

The  ductus  arteriosus  is  at  first  almost  as  large  as  the  pulmonary 
trunk;  and  nearly  the  whole  of  the  blood  from  the  right  ventricle 
passes  through  it  to  the  aorta,  only  an  insignificant  quantity  being 
distributed  to  the  lungs.  But  as  the  lungs  become  developed,  the 
pulmonary  branches  increase  in  size,  though  not  sufficiently  to  receive 
all  the  blood  of  the  pulmonary  trunk.  At  the  termination  of  foetal 
life,  in  man,  the  ductus  arteriosus  is  about  as  large  as  either  of  the 
pulmonary  branches ;  and  a  considerable  portion  of  the  blood,  there- 
fore, coming  from  the  right  ventricle,  still  passes  onward  to  the  aorta 
without  being  distributed  to  the  lungs. 

But  at  birth,  when  the  lungs  begin  the  performance  of  respiration, 
they  receive  a  greater  supply  of  blood.  The  right  and  left  pulmonary 
branches  enlarge,  so  as  to  become  the  principal  divisions  of  the  pul- 
monary trunk  (Fig.  249).  The  ductus  arteriosus  at  the  same  time 

diminishes  in  size,  and  is  soon  obliterated. 
It  remains,  in  the  adult,  as  an  impervious 
cord,  running  from  the  bifurcation  of  the 
pulmonary  artery  to  the  under  side  of  the 
arch  of  the  aorta.  The  obliteration  of 
its  cavity  is  usually  completed  by  the 
tenth  week  after  birth.  (Guy.) 

The  interventricular  septum,  by  which 
the  two  ventricles  are  separated  from 
each  other,  is  formed  at  an  early  date ; 
but  the  interauricular  septum  remains  for 

a  long  time  incomplete,  being  perforated 
HEART  OP  INFANT,  showing  the  disap-    . 

pearance  of  the  arterial  duct  after  bv  an  oval-shaped  opening,  the  foramen 
btrth.-i.Aoru.  2.  Pulmonary  artery.  ovale  which  allows  a  free  passage  from 

3, 8.  Pulmonary  branches.  4.  Ductus      . 

arteriosus  becoming  obliterated.  the  right  auricle   to   the   left.      The   exist- 

ence of  the  foramen  ovale   and   ductus 

arteriosus  gives  rise  to  a  peculiar  crossing  of  the  streams  of  blood 
in  the  liriirt,  eharacteri.-t  ic  of  foetal  life,  as  follows: 

In  the  foetus  the  two  venae  cavse  open  into  the  right  auricle  on  dif- 
ferent planes  and  in  diflerent  directions.  While  the  superior  vena  cava 
is  situated  anteriorly,  and  is  directed  downward  and  forward,  the  in- 
ferior is  situated  posteriorly,  and  joins  the  auricle  in  a  direction  from 


DEVELOPMENT    OF    THE    VASCULAR    SYSTEM.       699 


FIG.  250. 


right  to  left.  A  nearly  vertical  curtain  or  valve  projects  at  the  same 
time  behind  the  orifice  of  the  superior  vena  cava  and  in  front  of  the 
orifice  of  the  inferior.  This  curtain  is  formed  by  the  incomplete  septum 
of  the  auricles,  which  terminates  inferiorly  and  toward  the  right  in  a 
crescentic  border,  at  the  foramen  ovale.  The  stream  of  blood,  coming 
from  the  superior  vena  cava,  falls  in  front  of  this  curtain,  and  passes 
downward,  through  the  auriculo-ventricular  orifice,  into  the  right  ven- 
tricle. But  the  inferior  vena  cava,  owing  to  its  posterior  and  trans- 
verse position,  opens,  properly  speaking,  not  into  the  right  auricle, 
but  into  the  left.  Its  stream  of  blood,  falling  behind  the  above-men- 
tioned curtain,  passes  across,  through  the  foramen  ovale,  into  the  left 
auricle.  This  direction  of  the  cur- 
rent from  the  inferior  vena  cava 
is  further  secured  by  a  second 
membranous  partition,  which  ex- 
ists at  this  period,  termed  the 
Eustachian  valve.  This  valve, 
which  is  very  thin  and  trans- 
parent (Fig.  250, /),  is  attached 
in  front  of  the  orifice  of  the  in- 
ferior vena  cava,  and  terminates 
by  a  crescentic  edge  toward  the 
left ;  thus  standing  between  the 
cavities  of  the  inferior  vena  cava 
and  right  auricle.  A  bougie,  placed 
in  the  inferior  vena  cava,  as  in 
Fig.  250,  lies  behind  the  Eusta- 
chian valve,  and  passes  through 
the  foramen  ovale,  into  the  left 
auricle. 

The  two  streams  of  blood,  there- 
fore, coming  from  the  superior  and 
inferior  venaB  cavae,  cross  each 
other  on  entering  the  heart. 
Owing  to  the  position  of  the  two 
veins  and  their  adjacent  valves,  the  stream  coming  from  the  superior 
vena  cava  enters  the  right  auricle,  while  that  from  the  inferior  passes 
transversely  into  the  left. 

The  relations  of  the  aorta,  pulmonary  artery,  and  ductus  arteriosus 
at  this  time  are  such  that  the  arteria  innominata,  the  left  carotid  and 
left  subclavian  arteries  are  given  off  from  the  arch  of  the  aorta,  before 
the  junction  of  the  ductus  arteriosus ;  and  thus  the  blood-currents  of 
the  two  vense  cavse  are  distributed,  after  leaving  the  ventricles,  to 
different  parts  of  the  body  (Fig.  251).  The  blood  of  the  superior 
vena  cava  passes  through  the  right  auricle  into  the  right  ventricle, 
thence  through  the  pulmonary  artery  and  ductus  arteriosus,  to  the 


HEART  OK  THE  HUMAN  FCETUS,  at  the  end  of 
the  sixth  month.  —  a.  Inferior  vena  cava. 
6.  Superior  vena  cava.  c.  Cavity  of  the  right 
auricle,  laid  open  from  the  front,  d.  Appendix 
auricularis.  e.  Cavity  of  the  right  ventricle. 
/.  Eustachian  valve.  The  bougie,  placed  in 
the  inferior  vena  cava,  can  be  seen  passing 
behind  the  Eustachian  valve,  just  below  the 
point/,  then  crossing,  behind  the  right  auricle, 
through  the  foramen  ovale,  to  the  left  side  of 
the  heart. 


700 


REPRODUCTION. 


FIG.  251. 


Diagram  of  the  CIRCULATION  THROUGH 
THE  FCETAL  HEART.—  a.  Superior  vena 
cava.  6.  Inferior  vena  cava.  c,  c,  c,  c. 
Arch  of  the  aorta  and  its  branches. 
d.  Pulmonary  artery. 


thoracic  aorta;  while  the  blood  of  the  inferior  vena  oavn,  entering  the 
left  auricle  and  left  ventricle,  passes  into  the  arch  of  the  aorta,  and  is 
distributed  to  the  head  and  upper  limbs.  The  two  streams,  therefore, 

in  passing  through  the  heart,  cross  each 
other  both  behind  and  in  front.  The 
venous  blood,  returning  from  the  head 
and  upper  limbs  by  the  superior  vena 
cava,  passes,  through  the  thoracic  and 
abdominal  aorta  and  the  umbilical  ar- 
teries, to  the  lower  part  of  the  body, 
and  to  the  placenta ;  while  that  return- 
ing from  the  placenta,  by  the  inferior 
vena  cava,  is  distributed  to  the  head 
and  upper  limbs,  through  the  vessels 
given  off  from  the  arch  of  the  aorta. 

This  division  of  the  streams  of  blood, 
during  a  certain  period  of  fetal  life,  is 
so  complete  that  Reid,*  on  injecting  the 
inferior  vena  cava  with  red,  and  the 
superior  with  yellow,  in  a  human  foetus 
of  seven  months,  found  that  the  red 
injection  had  passed  through  the  foramen  ovale  into  the  left  auricle 
and  ventricle  and  the  arch  of  the  aorta,  and  had  filled  the  vessels  of 
the  head  and  upper  limbs ;  while  the  yellow  had  passed  into  the  right 
ventricle,  pulmonary  artery,  ductus  arteriosus,  and  thoracic  aorta,  with 
only  a  slight  admixture  of  red  at  the  posterior  part  of  the  right  auricle. 
All  the  branches  of  the  thoracic  and  abdominal  aorta  were  filled  with 
yellow,  while  the  whole  of  the  red  had  passed  to  the  upper  part  of 
the  body. 

We  have  several  times  repeated  this  experiment  on  the  foetal  pig, 
when  about  one-half  or  three-quarters  grown,  first  washing  out  the 
heart  and  large  vessels  with  a  watery  injection,  to  prevent  their  obstruc- 
tion by  coagulated  blood.  The  injections  used  were  blue  for  the  supe- 
rior vena  cava,  and  yellow  for  the  inferior.  The  two  syringes  were 
managed,  at  the  same  time,  by  the  right  and  left  hands ;  their  nozzles 
being  held  in  place  by  an  'assistant.  When  the  points  of  the  syringes 
were  introduced  into  the  veins  at  equal  distances  from  the  heart,  and 
the  two  injections  made  with  equal  rapidity,  it  was  found  that  at  least 
nineteen-twentieths  of  the  yellow  injection  had  passed  into  the  left 
auricle,  and  nineteen-twentieths  of  the  blue  into  the  right.  The  pul- 
monary artery  and  ductus  arteriosus  contained  a  similar  proportion  of 
blur,  and  tin1  arch  of  the  aorta  of  yellow.  In  the  thoracic  aorta,  how- 
evrr.  then-  was  always  an  admixture  of  the  two  colors,  generally  in 
about  equal  proportions.  This  may  be  owing  to  the  smaller  size  of  the 


*  Edinburgh  Mi-dieal  and  Surgical  Journal,  1835,  vol.  xliii.,  p.  11. 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM.    701 

head  and  upper  extremities  in  the  pig,  as  compared  with  the  human 
foetus,  which  would  prevent  their  receiving  all  the  blood  coming  from 
the  left  ventricle ;  or  to  some  difference  in  the  manipulation  of  these 
experiments,  in  which  it  is  not  always  easy  to  imitate  the  force  and 
rapidity  of  the  blood  currents  in  the  living  body.  The  results,  however, 
leave  no  doubt  that,  up  to  an  advanced  stage  of  foetal  life,  most  of  the 
blood  from  the  inferior  vena  cava  passes  through  the  foramen  ovale  into 
the  left  side  of  the  heart ;  while  most  of  that  coming  from  the  head  and 
upper  limbs  passes  into  the  right  side  of  the  heart,  and  thence  outward 
by  the  pulmonary  trunk  and  ductus  arteriosus.  Toward  the  latter 
periods  of  gestation,  this  division  of  the  venous  currents  becomes  less 
complete,  owing  to  the  following  causes : 

First,  the  two  pulmonary  arteries,  as  well  as  the  pulmonary  veins, 
enlarge  in  proportion  to  the  increased  size  of  the  lungs ;  and  a  greater 
quantity  of  blood  from  the  right  ventricle,  instead  of  passing  through 
the  ductus  arteriosus,  is  distributed  to  the  lungs,  and,  returning  thence 
to  the  left  auricle  and  ventricle,  joins  the  stream  passing  out  by  the  arch 
of  the  aorta. 

Secondly,  the  Eustachian  valve  diminishes  in  size.  This  valve,  which 
is  very  large  at  the  end  of  the  sixth  month,  subsequently  becomes  atro- 
phied, and  at  the  end  of  gestation  is  too  small  to  exert  any  influence  on 
the  current  of  the  blood.  Thus,  the  cavity  of  the  inferior  vena  cava, 
at  its  upper  extremity,  ceases  to  be  separated  from  that  of  the  right 
auricle. 

Thirdly,  the  foramen  ovale  becomes  partially  closed  by  a  valvular 
partition  growing  from  behind  forward.  This  valve,  which  begins  to 
be  formed  at  a  very  early  period,  is  the  valve  of  the  foramen  ovale.  It  is 
a  thin,  fibrous  sheet,  attached  to  the  posterior  surface  of  the  auricular 
cavity  a  little  to  the  left  of  the  foramen  ovale,  and  projecting  by  its  free 
border  into  the  left  auricle.  It  accordingly  does  not  interfere  at  this 
time  with  the  flow  of  blood  from  right  to  left,  and  only  prevents  regur- 
gitation  from  left  to  right. 

But  as  gestation  advances,  while  the  heart  continues  to  enlarge,  and 
its  cavities  expand  in  every  direction,  the  fibrous  bundles,  forming  the 
valve  do  not  elongate  in  proportion.  The  valve,  accordingly,  becomes 
drawn  down  more  closely  across  the  foramen  ovale.  It  thus  comes  in 
contact  with  the  inter-auricular  septum,  and  unites  with  its  substance ; 
the  adhesion  taking  place  first  at  its  lower  and  posterior  portion,  and 
extending  gradually  upward  and  forward,  so  that  the  passage  from  the 
right  auricle  to  the  left  becomes  more  oblique. 

At  the  same  time  the  inferior  vena  cava  alters  its  position.  This 
vessel,  which  at  first  looked  transversely  toward  the  foramen  ovale, 
turns  partially  forward ;  and  as  the  Eustachian  valve  has  now  nearly 
disappeared,  some  of  the  blood  from  the  inferior  vena  cava  enters  the 
right  auricle,  while  the  remainder  still  passes  through  the  foramen 
ovale. 


702  REPRODUCTION. 

At  birth  a  change  takes  place,  by  which  the  foramen  ovale  is  com- 
pletely occluded,  and  all  the  blood  coming  through  the  inferior  vena 
cava  is  turned  into  the  right  auricle. 

This  change  depends  on  the  commencement  of  respiration,  by  which 
the  quantity  of  blood  passing  through  the  lungs  is  largely  increased. 
The  left  auricle,  thus  supplied  to  its  full  capacity  with  blood  returning 
from  the  lungs,  no  longer  admits  the  entrance  of  a  further  quantity 
through  the  foramen  ovale;  and  the  valve  of  the  foramen,  pressed 
backward  against  the  septum,  becomes  after  a  time  adherent  through, 
out,  and  obliterates  the  opening.  The  cutting  off  of  the  placental  cir- 
culation also  diminishes  the  volume  of  blood  in  the  inferior  vena  cava. 
It  is  evident  that  the  same  quantity  which  previously  returned  from 

FIG.  252. 


DIAGRAM  OF  THE  ADULT  CIRCULATION  THROUGH  THE  HEART.— cr,  a.  Superior  and  inferior  vense 
cavse.  6.  Right  ventricle,  c.  Pulmonary  artery,  dividing  into  right  and  left  branches.  <f.  Pul- 
monary vein.  e.  Left  ventricle.  /.  Aorta. 

the  placenta  by  the  inferior  vena  cava  on  the  right  side  of  the  inter- 
auricular  septum,  now  returns  from  the  lungs,  by  the  pulmonary  veins, 
on  the  left  side  of  the  same  septum ;  and,  the  pressure  being  thus 
equalized  in  the  right  and  left  auricles,  there  is  no  mixture  of  the  blood 
between  the  two. 

The  foetal  circulation  is  then  replaced  by  the  adult  circulation,  repre- 
sented in  Fi.ir.  252. 

That  portion  of  the  inter-auricular  septum,  originally  occupied  by  the 
foramen  ovale,  is  accordingly  formed,  after  birth,  by  the  valve  of  this 
foramen,  which  has  become  adherent  to  its  edges.  The  septum  in  the 
adult  heart  is  thinner  at  this  spot  than  elsewhere ;  and  presents,  on  its 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM.   703 

right  side,  an  oval  depression,  termed  the  fossa  ovalis,  indicating  the 
site  of  the  original  foramen  ovale.  The  fossa  ovalis  is  surrounded  by  a 
slightly  raised  ring,  the  annulus  ovalis,  representing  the  edge  of  the 
original  inter-auricular  septum. 

The  foramen  ovale  is  sometimes  completely  obliterated  within  a  few 
days  after  birth,  but  often  continues  partially  pervious  for  several  weeks 
or  months ;  and  it  is  not  unfrequent  to  find  a  small  aperture  remaining 
in  adult  life.  In  these  instances,  although  the  consolidation  of  the  inter- 
auricular  septum  is  incomplete,  yet  no  admixture  of  blood  takes  place 
between  the  two  sides  of  the  heart.  The  oblique  direction  of  the  pas- 
sage and  its  valvular  arrangement  prevent  any  regurgitation  from  left 
to  right ;  and  the  complete  filling  of  the  left  auricle  with  blood  from 
the  lungs  is  a  sufficient  obstacle  to  the  entrance  of  venous  blood  from 
the  right. 


CHAPTER  XVII. 
DEVELOPMENT  OF  THE  BODY  AFTER  BIETIL 

THE  newly-born  infant  is  still  far  from  a  condition  of  complete  de- 
velopment. The  changes  through  which  it  has  passed  in  foetal  life 
are  followed  by  others  during  infancy,  childhood,  and  adolescence. 
The  anatomy  of  the  organs,  their  physiological  functions,  and  even 
the  morbid  derangements  to  which  they  are  subject,  continue  to 
undergo  progressive  alterations  throughout  the  whole  course  of  sub- 
sequent life.  The  history  of  development  extends,  properly  speaking, 
from  the  earliest  organization  of  the  embryonic  tissues  to  the  complete 
formation  of  the  adult  body.  The  period  of  birth  is  only  a  single 
epoch  in  a  long  series  of  changes,  some  of  which  have  preceded,  while 
many  others  are  to  follow. 

The  weight  of  the  newly-born  infant  is  about  seven  pounds.  The 
middle  point  of  the  body  is  nearly  at  the  umbilicus,  the  head  and  upper 
limbs  being  still  large,  in  proportion  to  the  lower  limbs  and  pelvis. 
The  abdomen  is  larger  and  the  chest  smaller,  in  proportion,  than  in  the 
adult.  The  lower  limbs  are  still  partially  curved  inward,  so  that  the 
soles  of  the  feet  look  obliquely  toward  each  other,  instead  of  being 
directed  horizontally  downward,  as  at  a  subsequent  period.  The  arms 
and  legs  are  curled  forward  over  the  chest  and  abdomen,  and  all  the 
joints  are  in  a  semi-flexed  position. 

The  process  of  respiration  is  imperfectly  performed  for  some  time 
after  birth.  The  expansion  of  the.  pulmonary  vesicles,  and  the  accom- 
panying changes  in  the  circulation  at  birth,  far  from  being  instanta- 
neous, are  more  or  less  gradual,  requiring  an  interval  of  several  days 
for  their  completion.  Respiration  seems  to  be  accomplished,  during 
this  period,  to  a  considerable  extent  through  the  skin,  which  is  soft, 
vascular,  and  ruddy.  The  animal  heat  is  less  actively  generated  than 
in  the  adult,  and  requires  to  be  sustained  by  careful  protection,  and 
by  contact  with  the  body  of  the  mother.  The  young  infant  sleeps 
during  the  greater  part  of  the  time ;  and  wrhen  awake  exhibits  but 
few  manifestations  of  intelligence  or  perception.  The  special  senses 
sin-  comparatively  inexcitable,  and  even  consciousness  seems  present 
only  to  a  limited  extent.  Voluntary  motion  and  sensation  are  nearly 
absent;  and  the  almost  constant  irregular  movements  of  the  limbs, 
•  •liHTvable  at  this  time,  are  mainly  automatic.  Nearly  all  the  nervous 
phenomena  presented  by  the  newly-born  infant,  are  of  a  similar  nature. 
The  motions  of  its  hands  and  feet,  the  act  of  suckling,  and  even  its 
cries  and  the  contortions  of  its  face,  are  reflex  in  origin,  and  do  not 

704 


DEVELOPMENT    OF    THE    BODY    AFTER    BIRTH. 

indicate  any  active  volition,  or  distinct  perception  of  external  objects. 
There  is  but  little  nervous  connection  with  the  external  world,  and  the 
system  is  occupied  almost  exclusively  with  the  functions  of  nutrition 
and  respiration. 

The  difference  in  organization  between  the  newly-born  infant  and 
the  adult  is  represented,  to  some  extent,  in  the  following-  list,  which 
gives  the  relative  weight  of  the  most  important  organs  at  the  period 
of  birth  and  in  adult  age  ;  the  weight  of  the  entire  body  being  reck- 
oned, in  each  case,  as  1000.  The  relative  weight  of  the  adult  organs 
is  calculated  from  the  estimates  of  Cruveilhier,  Solly,  and  Wilson,  that 
of  the  organs  in  the  foetus  at  term  from  our  own  observations : 

Foetus  at  term.  Adult. 

Weight  of  the  entire  body     .         .         .  1000. oo  1000.00 

u    encephalon      .         .         ..  148.00  23.00 

"    liver        ....  37.00  29.00 

"    heart       ....  7.77  4.17 

"    kidneys  ....  6.00  4.00 

"    supra-renal  capsules        .  1.63  0.13 

"            "    thyroid  gland           .         .  0.60  0.51 

a            "    thymus  gland          .         .  3.00  0.00 

It  appears  that  most  of  the  internal  organs  diminish  in  relative  size 
after  birth,  owing  principally  to  the  increased  development  of  the 
osseous  and  muscular  systems,  both  of  which  are  very  imperfect 
throughout  intra-uterine  life,  but  come  into  activity  during  childhood 
and  youth. 

The  remains  of  the  umbilical  cord  begin  to  wither  within  twenty- 
four  hours  after  birth,  and  become  completely  desiccated  by  about  the 
third  day.  A  superficial  ulceration  then  takes  place  at  its  point  of 
attachment  and  it  is  thrown  off  within  the  first  week.  After  separa- 
tion of  the  cord,  the  umbilicus  becomes  completely  cicatrized  by  the 
tenth  or  twelfth  day.  (Guy.) 

An  exfoliation  and  renovation  of  the  cuticle  takes  place  over  the 
whole  body  soon  after  birth.  According  to  Kolliker,  the  eyelashes, 
and  probably  all  the  hairs  of  the  body  and  head,  arc  thrown  off  and 
replaced  by  others  within  the  first  year. 

The  teeth  in  the  newly-born  infant  are  but  partially  developed,  being 
still  enclosed  in  their  follicles  and  concealed  beneath  the  gums.  They 
are  twenty  in  number,  namely,  two  incisor,  one  canine,  and  two  molar 
teeth  on  each  side  of  each  jaw.  At  birth  there  is  a  thin  layer  of  den- 
tine and  enamel  covering  their  upper  surfaces,  but  the  body  and  fangs 
of  the  tooth  are  formed  subsequently  by  progressive  elongation  and 
ossification  of  the  tooth-pulp.  The  fully  formed  teeth  emerge  from  the 
gums  in  the  following  order:  The  central  incisors  in  the  seventh  month 
after  birth ;  the  lateral  incisors  in  the  eighth  month ;  the  anterior  molars 
at  the  end  of  the  first  year ;  the  canines  at  a  year  and  a  half ;  and  the 
second  molars  at  two  years  (Kolliker).  The  eruption  of  the  teeth  in 

2U 


706  REPRODUCTION. 

the  lower  ja\v  generally  precedes  by  a  short  time  that  of  the  correspond- 
ing teeth  in  the  upper  jaw. 

During  tin-  seventh  year  a  change  begins  to  take  place  by  which  the 
first  set  of  teeth  are  replaced  by  the  second  or  permanent  set.  The 
anterior  permanent  molar  tooth  first  shows  itself  just  behind  the  pos- 
terior temporary  molar,  on  each  side.  This  happens  at  about  six  and 
a  half  \  ears  after  birth.  At  the  end  of  the  seventh  year  the  middle 
incisors  arc  thrown  oil'  and  replaced  by  corresponding  permanent  teeth, 
of  larger  size.  At  the  eighth  year  a  similar  exchange  takes  place  in 
the  lateral  incisors.  In  tho  ninth  and  tenth  years,  the  anterior  and 
second  molars  are  replaced  by  the  anterior  and  second  permanent  bi- 
cuspid teeth.  In  the  twelfth  year,  the  canine  teeth  are  changed.  In 
the  thirteenth  year  the  second  permanent  molars  show  themselves ;  and 
from  the  seventeenth  to  the  twenty-first  year,  the  third  molars,  or 
"  wisdom  teeth,"  emerge  from  the  gums,  at  the  extremities  of  the 
dental  arch.  (Wilson).  The  jaw,  therefore,  in  the  adult  condition, 
contains  three  teeth  on  each  side  more  than  in  childhood,  making  in 
all  thirty-two  permanent  teeth;  namely,  on  each  side,  above  and 
below,  two  incisors,  .one  canine,  two  bicuspids,  and  three  permanent 
molars. 

The  generative  apparatus,  which  is  inactive  at  birth,  begins  its  func- 
tional activity  from  the  fifteenth- to  the  twentieth  year.  The  general 
configuration  of  the  body  alters  at  this  period,  and  the  distinction  be- 
tween the  sexes  becomes  more  marked.  The  beard  is  developed  in  the 
male ;  and  in  the  female  the  breasts  assume  the  size  and  form  charac- 
teristic of  puberty.  The  voice,  which  is  shrill  and  sharp  in  infancy 
and  childhood,  becomes  deeper  in  tone,  and  the  countenance  assumes  a 
more  sedate  expression.  After  this  period,  the  muscular  system  in- 
creases still  farther  in  size  and  strength,  and  the  consolidation  of  the 
skeleton  also  continues ;  the  bony  union  of  its  various  parts  not  being 
entirely  accomplished  until  the  twenty-fifth  or  thirtieth  year.  Finally, 
all  the  organs  of  the  body  arrive  at  the  adult  condition,  and  the  entire 
process  of  development  is  then  complete. 


INDEX. 


Abdomen,  movements  of,  in  respiration,  236. 
Abdominal  plates,  of  the  blastoderm,  620. 
Abdominal  preg-iiancy,  606. 
Abdominal  respiration,  237. 
Abducens  nerve,  467. 

origin  of,  467. 

physiological  properties  of,  467. 
Absorption.  195. 

by  the  intestinal  villi,  196. 

by  blood- vessels,  198. 

by  laeteals,  200. 

of  carbo-hydrates,  203. 

of  oxygen  in  respiration,  240. 

of  serum  in  ruptured  Graafian  follicle,  609. 

by  the  vitelline  circulation,  638. 

of  oxygen  in  animals  and  vegetables,  232. 

by  the  blood,  251. 

by  the  fowl's  egg.  in  incubation,  644. 

by  the  placenta,  659. 

by  different  tissues.  312. 
Absorption  and  transudation,  in  the  living 

body.  317. 
Absorption  bands,  94. 

of  blood,  95. 

of  bile,  100. 

of  urine.  102. 

of  chlorophylle.  103. 

of  Pettenkofer's  test,  112, 113. 
Accommodation,  of  the  eye  for  vision  at 
different  distances,  539,  541. 

mechanism  of,  5-i:>. 

normal  limits  of.  543. 
Acid,  uric,  45,  117,  3;',2. 

lactic,  59. 155. 

carbonic,  50,  240,  242,  246,  253. 

stearic.  65. 

of  the  gastric  juice,  155. 

hydro-chloric,  155. 

tartaric,  250. 

oxalic,  339. 

perosmic,  344. 

oxalic,  from  decomposition  of  albumenoid 
substances,  71. 

phospho-glyceric,  105. 

glycocholic,  108. 

taurocholic,  109. 

Acid  biphosphate,  of  the  urine,  45,  329. 
Acid  fermentation,  of  milk,  124. 

of  bread.  1'Jii. 

of  the  urine.  338. 

Acid  and  alkaline  animal  fluids,  44. 
Acidification  of  fats,  in  saponiflcation,  65. 

by  the  pancreatic  juice,  87, 1<>9,  172. 
Acidity,  of  the  urine,  45,  325,  329. 

of  the  gastric  juice,  155. 
Action  of  arrest,  488,  489,  507. 
Action,  reflex,  of  the  nervous  system,  359. 

of  the  spinal  cord,  401. 

of  the  medulla  oblongata,  442,  443. 
Acuteness,  of  touch  in  different  regions,  511. 

of  smell  in  animals.  519. 

of  vision,  in  the  retina,  533. 
Adipose  tissue,  66. 

uses  of,  70. 

digestion  of,  163. 
Adult  circulation,  690. 

establishment  of,  at  birth,  702. 
Air,  atmospheric,  composition  of,  240. 

quantity  of,  used  in  respiration,  239. 

changes  in,  by  respiration,  210. 

vitiation  of.  by  continued  respiration,  246. 
Air  cells,  of  lungs,  234,  235. 


Air  chamber,  in  fowl's  egg,  5sn. 
Air  space,  estimates  of,  for  ventilation,  240. 
Ala  ciiierea.  in  medulla  oblongata,  441. 482. 
AlbugJ  neons  tunic,  of  the  ovary,  590. 
Albumen.  80. 

of  egg,  80, 588. 

of  blood,  80. 

vegetable.  84,  85. 

in  milk.  12:5. 

ill  saliva,  143. 

of  blood-plasma,  222. 

in  the  urine,  335. 
Albumenoid  substances.  73. 

general  characters  ot,  73. 

origin  of.  79. 

classification  of,  79. 

source  and  destination  of,  90,  91. 
Albuminous  matters,  80. 

proportion  of.  in  food,  130. 

daily  consumption  of,  132. 

conversion  of,  into  peptone,  139. 

digestion  of,  159,  1(59,  173. 
Albuminous  secretion,  of  the  oviducts, 

587.  f>ss. 

-   of  the  Fallopian  tubes,  617. 
Albuminous  urine.  335. 
Alcohol,  from  fermentation  of  glucose.  57. 

action  of,  on  albuminous  ferments.  85. 
Alimentary  canal.  136. 

different  parts  of,  137. 

development  of,  672. 
Alkalescence,  of  the  blood,  44,  22:;. 

of  urine,  340. 

Alkaline  fermentation,  of  the  urine,  339. 
Alkaline  phosphates,  44. 

carbonates.  46. 

animal  fluids,  44. 
Allantois,  640. 

formation  of.  641, 642. 

physiological  action  of,  642. 

circulation  of,  690.  . 
Amblyopia,  454, 
Ammonia,  in  the  air,  240. 
A  in  in  on  io-iuau  iK'si  an  phosphate,  840. 
Amnesic  aphasia,  432. 
A  in ii  ion.  640,645. 

formation  of,  641. 

in  man,  645. 

contact  of,  with  chorion,  646. 
Amiiiotic  cavity.  641. 

enlargement  of.  during  pregnancy,  645, 646. 
Amniotic  fluid,  646. 
Amniotic  folds,  641. 
Amoeba,  220. 

movements  of,  221. 
Amoeboid,  movements  of  the  white  globules 

of  the  blood,  220. 

Ampulla,  of  the  membranous  labyrinth,  55<». 
Analysis,  of  animal  fluids,  31. 
Anaesthesia,  401. 
Angular  convolution,  of  the  brain,  416. 

localization  of  sight  in,  439. 

excision  of,  in  the  dog,  431. 
Animal  charcoal,  as  a  decolorixer,  93. 
Animal  fluid,  acid  and  alkaline,  44. 

internal  renovation  of,  323. 
Animal  heat,  258. 

quantity  of,  produced  in  the  body,  260. 

production  of,  262. 

sources  of,  271. 

Animalcules,  infusorial,  577. 
Annulus  ovalis,  703. 

707 


708 


INDEX. 


Anterior  chamber,  of  the  eyeball,  f>22. 

Anterior  columns,  of  the  spinal  cord,  383. 

excitability  of,  3'J2. 

connections  of.  with  brain,  386. 
Anterior  pyramids.  377. 

decussation  of,  38'..  :;(.)7. 
Anus,  formation  of,  in  the  embryo,  621. 

imperforate,  673. 

Aorta,  formation  of,  in  the  embryo,  688,  691. 
Aphasia.  >:,-'. 

amnesic.  432. 

ataxic,  I:;:;. 
Apparatus,  circulatory,  274. 

registering.  368. 

ferment.  333. 

for  measuring  duration  of  electric  spark, 

Appendix    vermiform!*,  formation    of, 
878. 

Appetite,  disturbance  of,  from  nervous  con- 
dition-, 166. 

Aqueous  humor.  522. 
Arbor  vitae  uteriiia.  591. 

Arch  of  the  aorta,  formation  of,  691. 
Arch  of  4'orti.  565. 

A  relies,  cervical.  690. 
Area  opaca.  (i2t'1. 
Area  pellucida,  r.l'.t,  r.2H. 
Area  vasculosa.  ti:;5,  <;::r.,  637. 
Arrest,  action  of.  -iss.  507. 

of  heart,  by  galvanizing  the  pneumogastric 

nerve,  489. 
Arterial  circulation,  285. 

development  of,  690. 
Arterial  pressure,  292. 
Arterial  pulse.  286. 

traces  of,  by  sphygmograph,  289,  290,  291. 

characters  of,  287. 
Arteries,  285. 

movement  of  blood  in;  286. 

increased  curvature  of,  in  pulsation,  2!S7. 

muscularity  and  eontractibility  of,  500,  501. 

rhythmical  contraction  of,  501. 

contraction  and  dilatation  of,  under  nerv- 
ous influence,  502. 

vitelline,  638. 

omphalo-mesenteric,  688. 

vertebral.  688.  690. 

umbilical,  690. 
Articulation,  conditions  of,  444,  445,  495. 

in  facial  paralysis,  IT:;. 
Aryteiioid  cartilages,  238. 
Ascaris  lumbricoides,  573. 
Asparagus,  effect  of,  on  the  urine,  335. 
Ataxia,  loeomotor,  408. 
Ataxic.  aphasia.  .]:;::. 

Atropine,  absorption  of,  by  the  cornea,  317. 
Attitude,  and  locomotion, influence  of  spinal 

cord  on,  406. 

Auditory  hairs,  560. 
Auditory  nerve,  177. 

origin  of,  477. 

physiological  properties  of,  478. 

distribution  of,  in  the  membranous  laby- 
rinth, 560. 
Auditory  spots,  in  membranous  labyrinth, 

560. 

A  ii  ricu  lo- vent  ricnlar  valve**,  275,  276. 
Axis,  ce-rebro-spinal,  structure  of,  378. 
Axis  cylinder,  of  nerve  fibres.  :U5,  346. 
Azygous  veins,  formation  of,  694. 

Bacteria.  580. 

Bacterium  termo.  in  putrefaction,  78.  580, 
66L 

Base,  of  brain,  377. 

of  crura  oerebri.  171. 
Belladonna,  action  of,  on  the  iris.  317. 
Bile.  174. 

coloring  matters  of,  98,  99,  177. 

spectrum  of.  100. 

organic  salts  of.  IDS. 

physical  proper! iesiuid  composition  of.  177. 

secretion  ;ind  discharge  of,  180. 

daily  quantity  of.  l.vj. 

physiological  action  of.  183. 
Bile  duets.  ca|>illary,  177. 


Bile  tests.  Gmelin's,  178. 
Biliary  salts.  108. 

formation  of,  lid. 

Pettenkofer's  test  for,  110. 

in  bile,  179. 

reaction  of,  with  gastric  juice,  184. 

disappearance  of,  in  the  intestine,  185. 

presence  of,  in  the  urine.  334. 
Biliary  list u la.  179, 180. 183, 184, 185. 
Bilimbine.  «.»s,  177. 
Bilivcrdinc.  W,  177. 

spectrum  of,  100. 

production  of.  from  bilirubine,  101. 
Binocular  vision,  546. 
Bi phosphate,  acid,  of  the  urine.  45,  329. 
Bladder,  gall,  as  a  receptacle  for  the  bile,  180, 
181. 

contraction  and  evacuation  of,  in  diges- 
tion, 1*2. 

Bladder,  urinary,  as  a  reservoir  for  the  urine, 
410; 

contraction  and  evacuation  of,  410. 411,  412. 

development  of,  in  the  embryo,  676. 
Blastoderm.  618,  t»2 .. 

external  and  internal  layers  of.  618. 

intermediate  layer  of,  619. 

formation  of,  in"  fowl's  egg,  624. 

extension  of,  in  incubation,  626. 

folds  of,  628. 
Blastodermie  layers,  618,619. 

formation  of,  624,  627. 
Blind  spot,  in  the  eye,  529. 

illustration  of.  530. 

Blindness,  unilateral,  from  lesions  of  the 
brain.  430,  431.  454. 

from  lesion  of  the  optic  nerve,  453,  454. 
Blood,  212. 

diagnosis  of.  218. 

plasma  of,  221. 

coagulation  of,  224. 

quantity  of,  in  the  body,  2:u>. 

chaimvs  in,  by  respiration,  251. 

temperature  of,  259,  265. 

cooling  of,  in  lungs  and  skin,  266. 

circulation  of,  274. 

formation  of,  in  the  embryo,  635. 
Blood  current,  rapidity  of,  in  arteries,  293. 

in  veins,  297. 

in  capillaries,  300. 
Blood  globules,  red,  212. 

physical  properties  of,  212. 

structure  of,  214. 

alteration  of,  by  desiccation,  214. 

by  imbibition  of  water,  214. 

by  acid  and  alkaline  solutions,  215. 

composition  of,  215. 

characters  of.  in  man,  213. 

in  animals,  216. 

physiological  function  of,  219. 

in  urine,  337. 
Blood  globules,  white.  219. 

amoeboid,  movements  of,  220. 

physiological  functions  of,  221. 
Blood  pressure,  in  the  auricles  and  ven- 
triHes,  285. 

in  the  arteries,  292. 
Blood  stains,  recognition  of,  218. 
Blood-vessels,  muscularity  and  contract- 
ility of.  500. 

influence  of  sympathetic  nerve  on,  502. 

tonic  contraction  of,  505. 

reflex  contraction  and  dilatation  of,  507. 

development  of,  in  the  embryo,  635. 

of  the  chorion,  647. 

of  the  placenta,  657,  658. 
Body,  of  the  uterus,  590. 
Bones,  composition  of,  38. 

os.silieation  of,  40,  644, 706. 
Bra  in.  375,  413. 

of  alligator.  :V75. 

human,  :',7C.. 

in  vertical  section.  379. 

connections  of  spinal  cord  with,  385. 

ti>snres  and  convolutions  of.  413,  111. 

ccntresof  motions  and  sensation  in,  426,  4"". 

base  of.  :'>77. 

formation  of,  in  the  embryo,  667. 


INDEX. 


709 


Bread.  124. 

Broad  ligaments,  of  the  uterus,  685. 

Bronchi,  division  of,  234,  285. 

Bronchial  tubes,  ultimate,  235. 

Brunner's  glands,  188. 

Bulb,  olfactory,  448. 

Butter,  124. 

Butyrine,  124. 

Canal,  alimentary,  136. 

development  of,  672. 

i-entral,  of  spinal  cord,  374. 

medullary,  in    the   embryo,  620,  630,  631, 
667. 

of  Petit,  523. 

of  Schiemm,  520. 
Canals,  of  Cuvier,  692. 

semicircular,  559. 
Cane  sugar.  59. 
Capillary  blood-vessels,  297. 

of  the  intestinal  villi,  199. 

absorption  by,  198. 

movement  of  the  blood  in,  300. 

of  the  lungs,  235. 

of  the  pia  mater,  298. 

of  the  chorion  and  placenta,  657. 
Capillary  circulation,  297. 

in  web  of  frog's  foot,  300. 

causes  of,  301. 

rapidity  of,  302. 

local  variations  of,  304. 
Capillary  plexus.  299. 
Capsule,  internal,  378,  417,  421,  434. 

external,  417. 

Caput  coli,  formation  of,  673. 
Carbo-hydrates,  49. 

in  the  food,  52, 54, 120. 

insufficient  for  nutrition,  121. 

daily  consumption  of,  132. 

digestion  and  absorption  of,  172,  203. 
Carbon,  in  organic  substances,  33,  49. 

daily  consumption  of,  132. 
Carbonate,  ammonium,  from  decomposition 
of  urea,  115. 

in  decomposing  urine,  340. 
Carbonates,  lime  and  magnesium,  41. 
Carbonates,  sodium  and  potassium,  46. 
Carbonic  acid,  deoxidation  of,  by  plants, 
50. 

quantity  of,  in  the  atmosphere,  50. 

produced  from  fermentation  of  glucose,  57. 

exhaled  in  the  breath,  134. 

produced  in  respiration,  242. 

quantity  of,  exhaled  per  hour,  243. 

discharged  by  the  kidneys  and  skin,  243, 244. 

effects  of,  on  respiration,  246. 

proportion  of,  to  oxygen  used  in  respira- 
tion, 248. 

exhalation  of,  from  the  blood,  253. 

condition  of,  in  the  blood,  254. 

source  of,  in  the  tissues,  255. 

discharge  of,  by  fowl's  egg,  in  incubation, 

644. 
Cardiac  circulation,  274,  275,  276. 

in  the  fffitus,  698,  699,  700. 
Cardiograph.  283. 
Cardiographic  trace,  284. 
Carotitt  arteries,  formation  of,  in  the  em- 
bryo, 691. 
Caseine.  81. 
Catalysis,  76. 

Catoptric  images,  in  the  eye,  541,  542. 
Caudate  nucleus,  of  the  corpus  striatum, 

4-6. 
Cells,  nerve,  356. 

pyramidal,  in  brain,  418. 

giant,  419,  429. 

of  the  cerebellum,  435. 

of  the  sympathetic  ganglia,  496. 
Cellulose,  of  starch.  51. 
Centre,  nervous,  definition  of,  359. 
Centre,  of  language  in  cerebral  convolutions, 
432. 

of  respiration  in  medulla,  oblongata,  441. 

of  vision  in  angular  convolution,  439 
Centres,  motor,  in  cortex  of  brain,  426, 427, 
429,  430. 


Centrifugal  and  centripetal  degeneration 

of  divided  nerve  fibres,  389,  390. 
Cereal  grai  ns.  composition  of,  125. 
Cerebellum,  376, 435. 

peduncles  of,  377.  378,  386, 435. 

convolutions  of,  435. 


physiological  properties  of,  435 
effects  of  injury  or  ren 


injury  or  removal  of,  436. 

development  of,  668. 
Cerebral  ganglia,  376. 
Cerebral  vesicles,  in  the  embryo,  668. 
Cerebrine,  106. 
Cerebro-spinal  axis,  structure  of,  378. 

formation  of,  in  the  embryo,  620,  630,  631, 

632. 
Cerebrum.  375,  376. 

vertical  section  of.  379. 

fissures  and  convolutions  of,  413,  414. 

centres  of  motion  and  sensation  in,  426, 430. 

development  of,  667. 
Cervical  arches,  690. 
Cervical  enlargement,  of  spinal  cord, 

375. 

Cervical  fissures,  677. 
Cervix  uteri,  591. 

in  pregnancy,  664. 

in  the  foetus,  686.  , 
Chalazje,  588. 

Chalaziferous  membrane,  588. 
Channels,  for  sensation  and  motion  in  the 

spinal  cord,  392. 
Cheese,  124. 

Chest,  movements  of,  in  respiration,  236. 
Chiasma,  of  the  optic  nerves,  449,  451,  452, 

453,  454. 

Chick,  development  of,  626. 
Chloride,  sodium,  41. 

in  the  body,  42. 

in  the  food,  42. 

usefulness  of.  42. 

discharge  of,  43. 

in  the  urine.  330. 
Chloride,  potassium,  43. 
Chlorophylle,  103. 

action  of,  in  plants,  50, 104. 
Cholesterine,  71. 

in  the  bile,  72. 

physiological  relations  of,  72. 
Cholic  acid,  108, 109. 
Choiidrine,  89. 
Chorda  dorsalis,  620,  633,  634. 
Chorda  tympani.  476. 

influence  of,  on  circulation  and  secretion, 
476. 

on  the  sense  of  taste,  477. 
Chordae  vocales,  movement  of,  in  respira- 
tion, 238. 

action  of,  in  the  formation  of  the  voice,  486. 
Chorion.  645,  646. 

villosities  of,  647. 

blood-vessels  of,  647. 

office  of,  in  formation  of  the  placenta,  656. 
Choroid  coat,  of  the  eyeball,  520,  521. 
Chyle,  172. 

oily  granules  of,  66,  67, 197. 

composition  of,  320. 
Cicada  septendecim.  572. 
Cicatricula,  of  the  fowl's  egg,  587,  623. 

segmentation  of,  624. 
Ciliary  body.  521. 
Ciliary  muscle,  521.  543. 
Ciliary  processes,  521. 
Ciliary  nerves,  497. 
Circulation,  of  the  blood,  274. 

through  heart  and  lungs,  275,  276. 

arterial,  285. 

venous,  295. 

capillary,  297. 

general  rapidity  of,  303. 

influence  of,  on  local  temperature,  267. 

influence  of  sympathetic  nerve  on,  502. 

vitelline,  687. 

placental,  688. 
*  adult.  690. 
Circulatory  apparatus,  274. 

development  of;  687. 
Claiistmm,  417. 


710 


INDEX. 


Clot,  of  coagulated  blood,  225. 

in  ruptured  <  Jraalian  follicle.  609. 
<  o;iuniai>ilii.v,  ci  albumenoid  substances, 

of  the  yellow  and  white  yolk,  038. 
Coagulation.  75. 

oT  albumen.  KO. 
of  caseine.  M.  1-1. 
of  paraglobuline,  81. 

of  tibrinoiren.  *2. 
of  milk.  124. 
of  myosine.  s:'. 

of  peptom 

of  ibe  blood,  224 

(if  menstrual  blood,  t'uT. 
Coelilea.  ><•:; 

physiological  action  of,  565. 
Cold, 'resistance  to.  by  iiiiiinals,  270. 

effect  of,  when  excessive,  269. 
Coloring  m:Ul«  i  s.  H2. 

of  thel.lood. '.':;. 

of  the  hair  and  skin,  98. 

of  the  bile,  '.is.  •.«». 

of  the  urine,  101. 

of  green  plants,  103. 

of  the  retina,  534. 

Column,  vertebral,  formation  of,  r,:;:;.  r,:v>. 
Columns,  of  the  spinal  cord,  :!75,  3.S2. 

untcrior.  38 

lateral.  883,  :w7.  :i'.»l,  392. 

posterior,  :W4,  :&",  :;m. 

«»f  Clarke,  382. 

Of  '.oil,  408. 

ofT.irck,  :;:i:,. 
Commissure,  anterior,  of  brain.  420. 

gray,  of  spinal  cord,  :;71.  :'>>2. 

white,  of  spinal  cord,  :171,  383. 
Composition,  of  Fehl  ing's  liquor,  56. 

of  albumenoid substances,  7:>. 

of  albumen,  74. 

of  melanine,  98. 

of  eblorophylle.  103. 

of  milk,  li.':;! 

of  butter,  121. 

of  the  cereal  grains,  125. 

of  bread.  126. 

of  meat,  126. 

of  eggs,  127. 

of  potatoes,  128. 

of  beans,  12s. 

of  the  daily  food,  llXl,  132. 

of  starch,  130. 

of  fat,  130. 

of  saliva,  143. 

of  gastric  juice,  155. 

of  pancreatic  juice,  167. 

of  bil< 

of  Intestinal  juice,  190. 

of  red  blood';  !.,hnies,  215. 

Of  blood  plasma,  221. 

of  atmospheric  air,  210. 

of  lymph.  319. 

of  Ivinph  and  chyle,  ".20. 

of  the  urine,  327. 
Congenital    diaphragmatic  hernia, 

876. 

Congenital  inguinal  hernia.  684. 
Congenital  umbilical  hernia.  671. 
4  on-4  slion.  vascular,  from  division  of  sym- 
pathetic nerve.  5o2. 
4'4>ii<>s.  and  nxls.  of  the  retii 
<'oiiNtri«'tioiiM    of    Itaiivier,    in    nerve 

fibres,  :;ic.. 

Con  vol  it  tioiiH.  of  the  cerebral  hemispheres. 
19,  11::.  111. 

gray,  substance  of.  Us 

Structure  Of,  in  special  regions.  II1.'. 

first,  second,  and  third  frontal.  ll.">. 

anterior  and  posterior  central,  11C>. 

supra-marginal.  -IK'.. 

angular,  lit',.  i:;n,  r.;i. 

temporal,  IK'.. 

Cooking,    effect    of.   on    albumenoid    sub- 
stain  .  * 

on  bread. 

on  meat.  127. 

Oil  vegetables.  128. 


Coo rdination. of  muscular  power.in  spinal 

cord.  107. 

in  cerebellum.  I"/.. 
Cord,  spinal.  :J74.  :M. 

gray  substance  of,  374. 

white  substance  of,  375,  382. 

columns  of.  :;7"». 

arrangement  of  gray  and  white  substance 
in.: 

gray  substance  of,  381. 

transverse    sections  of,  374,  382,  :\*',,   :',%. 
406. 

connections  of,  with  brain,  385. 

transmission  of  motor  and  sensitive  im- 
pulses in,  370,387,390,892. 

sensitive  and  excitable  parts  of,  I'.'.H. 

channels  for  sensation  and  motion  in,  :i'.i2. 

erased  action  of,  397. 

as  a  nervous  centre,  401. 

reflex  action  of,  401,  405. 

influence  of,  on  attitude  and  locomotion, 
406. 

on  the  sphincter  muscles,  409. 

on  the  urinary  bladder.  411. 

formation  of,  in  the  embryo,  667. 
Cord,  umbilical.  661. 

spiral  twist  of,  t'.r.2. 

separation  of,  after  birth,  705.  • 
Cornea.  519,  520. 

inflammation  of,   after  division  of  trige- 
minus  nerve.  466. 

development  of,  669. 
Cormia.  of  the  uterus,  590. 
Corona  radiata.  :'.7s. 
Corpora  Ktriata.  :Mi. 
Corjwra  Wolfliaiia.  <>1. 
Corpus  <  allosiim.  :;TS,  |jn. 
Corpus  Inteiini.  *>'is. 

of  menstruation,  tios. 

of  pregnancy,  612. 

distinctions  between  them,  615. 
Corpus  striatiim,  :>7<*>. 

caudate  nucleus  of,  -U6. 

lenticular  nucleus  of,  417. 
Corti.  qrgan  of,  5tii. 

fibres  of.  565. 

arch  of,  565. 

<'ranial  nerves,  446. 
Creatine,  113. 

source  of,  114. 

conversion  of,  114. 
Creatiniiie.  111. 

in  the  urine,  :'.2!>. 
C remaster  muscle,  684. 
Crossed     aetioii,    of    the     cercbro-splnal 
nerves.  :',73. 

of  the  spinal  cord,  397. 

of  motor  and  sensitive  centres  in  the  brain, 
427,  430,  431. 

of  optic  nerves,  451. 

of  oculo  motorius  nerve,  456. 

of  patheticus  nerve.  15s. 

of  the  trigeminus,  1">(.). 

of  the  facial  nerve,  -17:'.. 

of  hypoglossal,  493. 
Crura  cerebri,  o78,  :;sf.,  120. 

base  of.  121. 

tegmentumof,  -Mil. 
C  rystalline  lens.  520.  5-J3. 

refractive  ]>ower  of,  523. 

function  of.  in  vision,  .VJ1. 

change  of  form  of.  in  accommodation,  541. 

development  of.  r>r><>. 
Cr.y stall ixaltle  nitrogenous  matters. 

in:,. 
Crystals,  of  stearine  and  palmitin. 

of  cholesterine.  71. 

of  hemoglobin. 


of  chlorophylle.  ID:',. 
of  biliarv  salts, 


ts,  ins. 

of  urea.  11.".. 

of  uric  aeid.:i::2. 

of  sodium  urate.  :;:'.7. 

of  oxalic  acid.  :;:;;». 

of  aminonio-magiiesiau  phosphate,  340, 
Ciimuliis  proltsjeriuh  '•"-• 
Cuticle,  exfoliation  of,  after  birth,  7n5. 


INDEX. 


711 


Cuvier,  canals  of,  692. 
Oysticereus  cellulosse,  574. 
reproduction  of,  575. 

Daily  ration,  of  food,  129. 

under  different  conditions  of  exercise,  132. 
I>eci<liia,  650. 

vera,  651. 

reflexa,  651. 

discharge  of,  in  abortion,  652. 

vera  and  reflexa.  contact  of,  663. 
Decussation,  of  cerebro -spinal  nerves,  373. 

of  anterior  pyramids,  377,  397. 

of  anterior  columns  of  spinal  cord,  383. 

of  posterior  columns  of  spinal  cord,  387. 

of  motor,  tracts  in  cerebro-spinal  axis,  397. 

of  sensitive  tracts  in  the  spinal  cord,  398. 

of  optic  nerves,  377,  451. 

of  oculomotorius,  456. 

ofpatheticus,  458. 

of  trigeminus,  459. 

of  facial,  473. 

of  hypoglossal,  493. 
Degeneration,  of  divided  nerve  fibres,  353. 

centrifugal  and  centripetal,  389. 

of  pyramidal  tracts  in  spinal  cord,  395,  398. 

of  columns  of  Goll,  408. 
Degeneration,  fatty,  of  decidua,  664. 

of  muscular  fibres  of  uterus,  after  delivery, 

665. 

Degenerations,  secondary,  in  the  spinal 
cord,  394. 

in  the  brain,  421. 
Deglutition,  nervous  mechanism  of,  443. 

influence  of  glossopharyngeal  nerve  on,  481. 

influence  of  pneumogastric  nerve  on.  487. 

connection  of  hypoglossal  nerve  with,  495. 

independent  of  sensibility  and  volition,444. 
Dehydration,  of  glucose,  59,  61,  206. 

of  taurocholic  acid,  109. 

of  creatine,  114. 
Dentition,  first,  705. 

second,  706. 
Deoxitlation,  of  carbonic  acid  and  water 

by  plants,  50. 
Deposits,  urinary,  336. 
Descent,  of  the  testicles,  683. 

of  the  ovaries,  685. 

of  the  uterus,  686. 
Development  of  spermatozoa,  594. 

of  eggs  in  the  ovaries,  600. 

of  the  impregnated  egg,  616. 

of  the  tadpole  and  frog,  619. 

of  the  embryo  chick,  623. 

of  the  umbilical  vesicle,  amnion  and  allan- 
tois,  639. 

of  the  amnion  and  chorion,  645. 

of  the  decidua,  650. 

of  the  placenta,  655. 

of  the  nervous  system,  607. 

of  the  organs  of  special  sense,  669. 

of  the  skeleton  and  limbs,  670. 

of  the  integument,  671. 

of  the  alimentary  canal,  672. 

of  the  liver,  675. 

of  the  lungs,  thorax,  and  diaphragm,  675. 

of  the  urinary  bladder  and  urethra,  676. 

of  the  lips  and  cheeks,  679. 

of  the  paiate,  679. 

of  the  Wolffian  bodies,  681. 

of  the  kidneys,  682. 

of  the  vascular  system,  687. 

of  the  aorta,  688. 

of  the  arteries,  690. 

of  the  veins,  692. 

of  the  hepatic  circulation,  695. 

of  the  heart  and  ductus  arteriosus,  697. 

of  the  body  after  birth,  704. 
Dextrine,  53. 
Diabetes  mellitus,  211,  233. 

temporary,  210. 

from  puncture  of  medulla  oblongata,  211. 
Diagnosis,  of  blood,  218. 
Dialysis,  75. 
Diaphragm.  236. 

action  of,  in  respiration,  236,  237. 

development  of,  675. 


Diaphragmatic  hernia,  congenital,  676. 
Diastase,  88. 

transforming  power  of,  on  starch,  76. 
Dichroism,  of  bile,  178. 
Dicrotie  pulse.  2'JO. 

Diet,  average.  129. 

variation  of,  under  exercise  and  labor,  132. 
Diffusible  and    non-diffusible    sub- 
stances, 74,  310. 

Diffusibility,  of  crystallizable  matters,  74. 

of  peptone,  75,  318. 

of  saline  solutions  in  water,  316. 

of  urea,  316. 

of  sugar,  gum,  and  albumen,  316. 

influence  on,  of  temperature,  repose,  and 

agitation ,  316. 
Digestion,  136. 

nature  of,  138. 

of  starch,  53,  148, 172. 

of  cane  sugar,  59. 

of  bread,  163. 

of  adipose  tissue,  163, 

of  muscular  flesh,  163. 

of  milk,  164. 

of  vegetables,  164. 

of  the  stomach,  by  its  own  gastric  juice,  160. 

of  albuminous  matters  by  trypsine,  168, 173. 

of  fats.  171. 

in  small  intestine,  164, 173, 192. 

connection  of  pneumogastric  nerve  with, 

Digestive  apparatus,  136. 

'fluids,  136,  138. 

artificial,  158. 
Dilator  nerves,  506. 

pupillae,  522. 

Direct  and  indirect  vision,  538,  553. 
Discus  proligerus,  602. 
Distance  and  solidity,  appreciation  of, 

548. 

Distoma,  573. 
Division  of  nerves,  347.    • 

of  nerve  fibres,  349. 

Dorsal  plates,  of  the  blastoderm,  620,  630. 
Ductus  arteriosus,  697. 

cochlearis,  564. 

venosus,  695. 
Duodenum,  fistula  of,  180. 

glandules  of,  188. 
Duration,  of  visual  impressions,  550. 

of  light,  necessary  for  perception,  550. 

of  sound  necessary  for  perception,  568. 

Ear,  external,  554. 

middle,  554.  555. 

internal,  558. 

development  of,  670. 
Ear-sand,  560. 
Earthy  phosphates,  41. 

in  the  blood,  224. 

in  the  urine,  330. 

deposits  of,  336. 
Ectoderm,  628. 
Egg,  584. 

growth  and  maturity  of,  585,  586. 

discharge  of,  from  the  ovary,  586. 

in  menstruation,  605. 

white  of,  588. 

expulsion  of,  from  oviduct,  589. 

passage  of,  through  Fallopian  tube,  606. 

impregnation  of,  606. 
Eighth  cranial  nerve,  477. 
Elastine,  90. 

Eleventh  cranial  nerve,  490. 
Embryo,  formation  of,  in  the  frog,  619. 

in  the  fowl's  egg.  623,  626. 

position  of,  in  the  egg,  629. 
Embryonic  spot,  619. 
Emmetropic  eye,  544. 
Emulsion,  64. 

of  fats  in  digestion,  140. 

by  pancreatic  juice,  167, 171. 
Encephalon.  375. 
End-bulbs,  of  the  conjunctiva,  349. 

termination  of  nerves  in,  350.  351. 
Eiidosmosis  and  exosmosis,  311. 
Eitdosmometer,  312. 


'12 


i  N  D  i :  x  . 


Enlargement,  cervical,  of  spinal  cord.  :::."•. 

lumbar.  :'.7">. 
Eiitodcrin. 

Ento/.oa.  reproduction  of.  .">T:'.. 
Epidermis,  exfoliation  of,  after  birth,  70T>. 
I  |»i<li<l>  inis.     u 

fonnatioo  ol 
Epirl«t*i». 

I  l»il<  |»s>  .  iVom  injury  of  the  spinal  cord.  in:;. 
Epithelium..  ;    salivary  ;_;iunds.  141. 

deposited  from  saliva.  1 12. 
Mric  follicles.  I.M. 

of  intestinal  villi.  1'A  198. 

of  capillary  blood-\  es-els,  299. 
Equilibrium,  sense  of,  562. 
Erethism,  sexual,  ">'.<7. 
Ether,  elimination  of.  by  the  urine 
Eiisfaehiau  tube.  ."••>. 

valve 

Evacuation,  of  the  pill  bladder,  in  diges- 
tion, 182. 

of  the  rectum  and  urinary  bladder,  4u'.i.-Un. 
Excrement.  I'.'!. 
Excrcmciltitious  mat  His.  ;;j). 

Excretion,  •  •~\. 

Exfoliation,  nf  the  hairs  and  cuticle,  after 

birth.  705. 
Exhalatioii.ofwatery  vapor  from  the  lun^s, 

38,  21.\ 

from  the  skin.  ::s.  '21 -2. 
from  the  e<_r^.  during  incubation,  01:;. 
I  x  osmosis,.  :,]] 

Expiration,  movements  of,  J;;7. 
Ex  I  <TII  a  I  capsu  le.  of < -erebral  hemisphere, 

Eye,  "il'.i. 

inflammation  of,  after  section  of  tritfeminus 

nerve,  466. 
development  of,-669. 
Eyeball.  519. 

immobility  of,  from  lesions  of  the  oculo- 

motoriui  nerve 

Eyelids,  movement  of,  in  winking,  473,  474. 
development  of.  0711. 

Face,  motor  nerve  of,  408. 
sensitive  nerve  of,  Kl'J. 
Facial  nerve,  468. 

origin  of.  His. 

branches  and  distribution  of,  469. 

physiological  properties  of.  468. 

effects  of  dividing,  470, 471. 

sen-ibilitj,  of,  -171,  17-. 

communications  of,  in  aqueduct  of  Fallo- 
]>\n*,  171. 

peripheral  and  central  lesions  of,  474. 

crossed  action  of,  47:5. 
Facial  paralysis.  171    17_> 

from  peripheral  and  central  lesions.  171. 

effect  of,  on  the  eyelids,  17n. 

on  the  nostrils,  17o. 

on  the  lips,  471. 

on  the  ears.  171. 

on  the  features  and  expression,  171. 

on  drinking  and  mastication,  17'J. 

on  articulation.  17:'-. 

on  the  sense  of  ta<te.  177. 
Fallopian  tubes. 

development  of.  ''>v-'.  • 

Fat.  production  of,  from  starch  and  suuar.  i'.s. 

Tjn. 
nee,-- -ary  for  nutrition,  121. 

•>  h   e(|iiivalent  of,  l:;|. 
aciditication  of,  by  pancreatic  juice,  .s",  ICi'.i 

•ion  of.  171. 
ab-orption  of.  l-.iT. 
in  the  bl.,., 

I   .11    Ulolllll- 

of  chyle,  C.7,  1'.'7. 
of  mi'lk.  C,7. 

in  liver  eel 

in  degenerated  muscular  lihp 

Fats.  f.l. 

jiliy-ical  pro],,Ttie-  ol 
origin  ol', 
viirietifx  ,,• 
emulsion  of.  ill. 


aj.o 

condition  ot.  in  living  body.  f 
extraction  of,  ii<;. 
production  of,  in  the  body.  us. 


.      . 
Fatty  «lcj;'ciicratioii.  of  the  decidua.  (144. 


physiological  relations  of.  70. 
tty  «lcj;'ciicratioii.  of  the 

ol  the  uterine  muscular  fibres,  after  deliv- 

ery. titi.i. 
Feature*.  deviation  of,  in  facial  paralysis,  17_>. 


retention  and  evacuation  of,  ln'.». 
Fecundation  of  the  e.u.ir.  595,606,  016. 
Fehlinj;"s  test,  for  glucose,  56. 
Female  organs  of  generation.  r-M. 

of  fro 

of  fov, 

of  pi- 

human  "<1»1. 
Eenestra  oval  is.  :..VJ. 

rotunda,  .v>n. 
Fermentation,  of  glucose,  57,  63. 

of  bread,  125. 

acid,  of  milk.  121. 

of  urine,  338. 

alkaline,  of  urine,  339. 
Ferment-apparatus,      for      saccharine 

urine,  888. 
Ferments,  characters  of,  75,  85. 

action  of,  in  digestion,  139. 

pancreatic.  N;,  n;s. 
Ferrocyaiiide.  potassium,  elimination  of, 

by  the  urine.  ::::!. 
Fibres,  nerve.  348. 
Fibres  of  1'orti.    i.  >. 
Fibrine.  82. 

ferment,  «2,  87,  22«. 
Fibrino^cii.  S2. 

in  blood  plasma.  222. 
Field  of  vision. 
Fifth  cranial  nerve,  4 :•<.». 
First  pair  of  cranial  nerves,  448. 
Fissure,  of  Sylvius,  113. 

of  Rolando.  11  1. 

parietal,  414. 

pni'central,  11'). 

frontal  in  dogs,  127. 
Fissure  of  the  palate.  080. 
Fissures,  cervical,  in  the  embrvo,  077. 
Fissures  and  convolutions  of  the  cerebral 

hemispheres,  11  I. 
Fistula,  gastric,  I.Vj. 

pancreatic,  166. 

duodenal,  180. 

biliarv.  179,  182, 183, 185, 186. 

intestinal.  190,  191,  193. 

Fixation,  point  of,  in  binocular  vision,  547. 
Fluids  of  the  body,  acid  and  alkaline,  44. 

digestive,  130.  138. 

internal  renovation  of,  323. 
Fluorescence,  of  bile,  178. 
Folds,  of  the  blastoderm,  628. 

amniotic.  641. 

visceral,  077.  090. 
Follicles,  salivary,  111. 

gastric,  151. 

of  Lieberkiihn.  189. 

closed,  of  small  intestine,  195. 
Follicle*,  Oraaflan,  686, 601. 

rupture  of,  (i(i2. 

in  menstruation,  605. 
Food.  mi. 

composition  of,  118.  120,  122,  123. 

daily  quantity  of.  I.1.'. 

under  different  conditions  of  exercise,  131, 
182. 

inlluence  of,  on  the  urine.  40. 

on  production  of  urea,  116, 117. 

of  uric  acid,  lls. 

on  secretion  of  saliva.  110.  147.  148. 

on  the  products  of  respiration,  249. 

on  heat-production,  202. 
Foramen  ovale. 

valve  of.  701. 

occlusion  of.  7(i:'.. 
Force,  nervous,  rapiditv  of  transmission  of, 

866. 
Eos*. a  ovalis.  7<i:'.. 


INDEX. 


13 


Fourth  cranial  nerve,  457. 
Fovea  centralis.  531,  532. 

Galvanism,  influence  of,  on  muscles,  361. 

on  motor  nerves,  362. 

Galvanic  currents,  direct  and  inverse,  ac- 
tion of,  363. 
Ganglia,  spinal,  374. 

ol factory,  375. 

optic,  376. 

cerebral,  376. 

sympathetic,  496.  498. 
Gang-lion,  ophthalmic,  457,  497. 

Qasserian,  460. 

geniculatum,  475. 

spheno-palatlhe,  475,  497,  518. 

Otic,  475,  497. 

petrosal,  479. 

jugular.  182. 

submaxillary,  497. 

semilunar.  498. 

coeliac,  498. 

impar,  499. 

Ganglion ic  system  of  nerves.  496. 
Gasseriiiii  g-aiig-lioii,  460. 
Gases,  intestinal,  87. 
Gastric  fistula.  152. 
Gastric  follicles.  151. 
Gastric. juice,  150. 

mode  of  obtaining,  153. 

secretion  of,  153. 

physical  properties  and  composition  of,  154. 

antiseptic  properties  of,  157. 

physiological  action  of,  159. 

self-digestion  of  stomach  by,  160. 

daily  quantity  of.  161. 

reabsorption  of,  1B5. 
Gelatine,  89. 
Gelatinous  albumciioid  substances, 

88. 

General  sensibility.  510. 
Generation,  reproduction  by,  570. 

spontaneous,  572. 

sexual,  582. 

female  organs  of.  584. 

male  organs  of,  592. 
Germ,  5S2. 

Germinal  membrane,  618. 
Germination,  of  plants,  production  of  heat 
in,  260. 

requisite  temperatures  for,  268. 
Germinal  ive  spot.  585. 
Germiiiativc  vesicle.  585. 

disappearance  of,  after  impregnation,  616. 
Giant  pyramidal  cells,  in  brain  cortex, 

419,  429. 
Gills,  233. 
Gland,  sub-maxillary,  142. 

vasomotor  and  dilator  nerves  of,  506. 
Glands,  lymphatic,  309. 
Glandular,  solitarije  and  agminatse,  195. 
Globules,  of  the  blood,  red,  212,  214,  215,  219, 
251. 

white,  219,  220,  221. 

of  the  lymph,  319,  320. 

Glomeruli,  of  the  Wolffian  bodies  and  kid- 
neys, 681. 

G  losso-la  bio-la  ry  uji'eal  paralysis, 445. 
Glosso-pharyng-eal  nerve,  479. 

connection  of,  with  sense  of  taste,  480. 

with  deglutition,  481. 

motor  properties  of,  481. 
Glottis,  respiratory  movements  of,  238. 

paralysis  of,  from  section  of  pneumogastric 
nerves.  485,  492. 

from  evulsion  of  spinal  accessory  nerve,  492. 

protection  of,   from    entrance  of   foreign 

bodies,  486,  487. 
Glucose,  54. 

composition  of,  54. 

production  of,  from  starch,  55. 

tests  for,  55. 

fermentation  of,  57,  333. 

conversion  of,  into  saccharose,  59. 

into  glycogen,  61. 

dehydration  of.  59.  61. 

production  of,i  n  the  liver,  from  gl  y cogen  ,206. 


Glucose,  accumulation  of.  after  death,  207. 
reabsorption  and  disappearance  of,  208. 
proportion  of,  in  arterial  and  venous  blood, 

accumulation    and    discharge  of,  by  the 
urine,  209,  332. 

quantitative  determination  of,  in  urine.  ::34. 
Gluten,  125. 
Glycerine,  produced  in  saponification,  65. 

influence  of,  on  production  of  glycogen  in 

liver,  206. 
Glycine.  108. 
Glycocholato.  sodium,  108. 

rotatory  power  ot,  on  polarized  light,  109. 

in  the  bile,  179. 

in  the  urine,  334. 
Glycocholic  acid.  108. 

production  of,  from  taurocholic  acid,  109. 
Glycogen,  60,  201. 

preparation  of,  60. 

production  of,  in  liver,  203. 

origin  and  formation  of,  204. 

under  varying  diet,  205. 

transformation  of,  into  glucose,  61,  206. 
Glycog-enic  function  of  the  liver,  206. 

in  the  foetus,  675. 
Gmelin's  bile-test.  99. 
Graafian  follicles,  585,  601,  602. 

rupture  of,  602. 

in  menstruation,  605.  608. 
Granulose  of  starch,  51. 
Grape  sugar.  54. 

Gray  commissure,  of  spinal  cord,  374. 
Gray  substance,  of  the  nervous  system, 
343. 

anatomical  characters  of.  356. 

physiological  action  of,  359. 

of  the  spinal  cord,  374.  381.  391. 

of  the  medullary  canal.  378. 
Gravity,  specific,  of  the  saliva,  142. 

of  gastric  juice.  154. 

of  bile,  177. 

of  intestinal  juice,  190. 

of  blood,  212. 

of  blood-globules,  212. 

of  blood  plasma,  212. 

of  lymph,  318. 

of  urine,  325. 

Groove,  medullary,  620,  630,  667. 
Gubernaculum  testis,  683. 
Gustatory  nerves,  464,  480,  515. 

Hair,  coloring  matter  of,  98. 

development  of,  671. 

exfoliation  of,  after  birth,  705. 
Hairs,  auditory,  560. 
Hare  lip,  679. 
Headache,  from  affection  of  the  fifth  cranial 

nerve,  463. 
Hearing1,  sense  of,  554. 

influence  of  trigerninus  nerve  on,  466. 

organ  of,  554. 
Heart,  274. 

valves  of,  275,  276. 

pulsation  of,  277. 

sounds,  movement  and  impulse  of,  277. 

transverse  section  of,  280. 

influence  of  pneumogastric  nerve  on,  189. 

development  of,  697. 
Heat,  internal,  in  animals,  258. 

in  vegetables,  259. 

quantity  of.  produced  in  body,  260. 

relations  of.  to  respiration,  263. 

local  production  of,  in  the  tissues,  264. 

sources  of,  271. 
Heat  unit,  260. 
Hemaplueiiic.  102. 
Hematine,  31. 
Ilematoidine,  99. 
Hemianresthesia,  401. 

from  cerebral  lesions,  433,  434. 
Hemiopia.  453. 
Hemipleffia.400. 

from  cerebral  lesions.  433.  434. 
Hemispheres,  cerebral,  376,  378,  380, 413. 

fissures  and  convolutions  of.  413,  414. 

horizontal  section  of,  417. 


711 


INI)  K  X  . 


functions  of,  -l 

localization  of  functions  in,  1JO. 
development  of,  in  tin-  embi  \ 
II,  ii.oulolnti.  .  ;;l    <..;;. 
.-  pect  rum  of,  li-l.  '.'  i. 
charges  of.  under  tin-  imluciice  o!  oxy-en. 

94. 

in  ditt'erent  animals,  '.'«'•. 
junction  of,  <.i7. 
in  blood  globules.  'Jl"). 
in  ropiiation.  'J.M. 

]I<>iiiorrliau-o.  arrot  of  by  coagulation,  229. 
from  tin-  uterus  in  menstruation,  0117. 
from  the  (iraaiian  follicle.  in  menstruation, 

fr<>m  the  placenta  and  uterus,  after  deliv- 

ery. r,r,::. 

ll«-i  iiiji.  umbilical,  in  tin-  embryo,  (171. 
congenital.  071. 
diaphragmatic,  070. 
inguinal.  Os(. 
llilM>riiati<»ii,  intlneiice  of.  on  respiration, 

241 
on  beat-production,  •_!<;:;. 

II  i|»|»nral<>.  sodium.  ll.\ 
Hlpparle  neid,  UK. 
llono.y.  .v.i. 

Horn**.  of  gray  substance,  in  the  spinal  cord, 

Horns.  of  the  uterus.  iV.H). 
Iliiiuor.  aqueon- 

Hyaloid  Iii4'iiibraii4>.  of  the  eyeball 
ll.xlratioii.  (,C  starch.  66,  do.  189. 

of  bilirubine,  Ktl,  1  (»•_». 

of  albuminous  matter.  i:;;i. 

of  Klycocholic  acid,  HIS. 

of  taurocholic  acid,  K".i. 

of  urea,  11."),  :;iu. 

of  stcarine,  d.>,  170. 
ll.Y'lrohilii  nhiiK  .  102. 
II.V4lr4K'arboiia<'4>4HiNKiibsfaii<M>s.:,:;.  I'.t. 
II,  ydro;;-4'ii.  introduction  and  discharge  of,  87. 

daily  consumption  of,  1  ::•_'. 
]Iyi»4'ra'sf  lu'sia.  after  injury  to  the  spinal 

cord.  :;!•'.'. 
II  >  !»<»:;  lossal  11  or  ve,  493. 

distribution  of,  494. 

physiological  properties  of.  494. 

connection  of,  v.  ith  mastication  and  deglu- 
tition, l'.ir>. 

with  articulation,  495. 

Idiocy,  condition  of  the  brain  in.  L'l. 

.  catoptric,  in  the  eye.  Ml. 

.  negative,  of  risible  object- 
luiporforato  aims.  07:;. 

lni|>r<'Kiiial4'4l  <'^«.  nucleus  of,  Ciic.. 
lni|>r<>Uii;it  ion.  '>s_'. 

of  the  e.L'^,  .")(.i".,  diK). 

immeiliate  etlects  of,  f>16. 
liii|»iils<  .  ,,f  the  heart.  L'77.  L's-J. 
Incisions,  of  Schmidt,  in  medullated  nerve 

libr. 

Incubation,  of  the  !'.-•.'. 
Incus. 

binlir,  <  I  vision.  680, 

Iiilaiif.  newly  born,  weight  and  general  con- 
dition of,  7nl. 

relative  sixe  of  organs  in,  7nr>. 

teeth  of.  7li:,. 
lnl<  ii«»r    iMMliinclcs    of     < 

luiii.  :;77.  :;N;. 
lnlus<»ria.  .'>77. 

re].roducti-'U  of.  :,7'.i. 
In^r4'4li4>nts.  of  the  b..dy. 

extraction  of,  ::]. 

Inorganic, 


albumeiioid.  :;i.  7:;. 

coloring.  B4 

cry-tallixable  nitrogenous.  :;!.  in."). 

inuniiiai  lu'rniu.  congenital,  684. 

I  IIOI^MIIK-  Niil»slaii«-4's.  in  the  body. 
Iiios4-ulati<»n,  of  l)lood-ves-i-ls.  :".• 

of  lymiilnttiev 

of  nerve-,  ::i7.  :;is. 


I  noscii  la  I  ion  .  of  peripheral  branches  of  tri- 

^eminus  nerve,  101. 
Inspiration,  movements  of,  •_':;(',. 
Insnla.  111.  117. 

centre  of  laii-ua-e  in.  V.',:'. 
I  ii<<-uiiiii4-iil.  termination  of  nerves  in,  :il'.i. 

development  of.  071. 
Internal  <*a|>sul4*.  :!7S,  117.  lL'1. 

injuries  of.  causing  hemipleKia  und  hemi- 

ana->thesia.  1:11. 
liilesliii.il  <li^4'slion.  I'.rJ. 
InK'stinal  JMI4M-.  iss. 

composition  of.  1  './'». 

action  of.  in  di-estion.  T.ll. 
IilK  sliiM  .  1:17. 

Kliinds  and  follicles  of,  188. 

digestion  in.  I'JL'. 

nerves  of,  I'.t'.t. 

development  of,  in  the  embryo,  Oiil.  072. 
I4><liiip.  elimination  of,  by  the  urine,  :'.:'.!. 
Iris.  .Vj(i.  :>L'l. 

niovemeiits  of.  4  .">'»,  -1  '.»;». 

influence  of  oculomotorius  nerve  on.  |.">7, 
489. 

Influence  of  sympathetic  nerve  on,  iw. 

development  of,  <i'i(.». 
Iron,  in  hemo-lobine,  !»7. 

in  melanine.  '.is. 

in  beef,  '.'7. 

in  fruits  and  vegetables,  «.)7. 
Irritability,  muscular,  HOI. 

nervous.  :;oo. 

of  sensitive  nerve  iibrcs.  :ido. 

of  motor  nerve  fibres.  :itil. 
Island  of  Koil,  41  1,  117,  !:;:;. 

Jacobs4>ii.  nerve  of,  47;T. 

.[MIIII<|MM>.  yi'llo\v  color  of  (lie  urine  in,  334. 

Jugular  ^aiiKli4»n,isj. 

Jiii<*4>.  gastric.  I-'.O. 

pancreatic,  io.">. 

iiue>tinal.  l.ss. 

Keratiiie.  90. 

KidiioyN.  circulation  in.  :'.n.~>. 

elimination  of  substances  by,  ::i'7.  :::'.!.  ::.!"). 

nerves  of,  r.i;i. 

(U:velo}>ment  of,  dvj. 

l.abyrinlli.  of  the  car,  f>.~>8. 

bony..V,l). 

membranous,  .",:,M. 

physiological  action  of,  ">01. 
I.a<*l4'al  V4'»*s4'ls.  absori>tion  by,  200. 
l,M4-l4-als  and  lymphatics,  in  digestion,  'J01. 


fermentation  of 
I.:M-IIII:«-.  lymphatic.  308. 
LamellHt4ed  shoatli.  of  nerves,  :',17. 

spiralis.  of  the  cochlea 
^'o.  articulate,  i:i_'. 
centre  of,  in  the  brain,  i:!2. 

iii(4-sf  iti4>.  1:17. 
contents  of,  l«i:l. 
development  of.  07:1. 
l.:ir>  iix.  functions  and  innervntion  of,  482, 

492. 

Lateral  4-oliimits.  of  the  spinal  cord,  383. 
sensibility  of,  ".'.M. 

excitability  of.  :  :!»•_'. 

,  iiH-dullary.  of  nerve-  fibres,  ",11. 

blastodermie,  externul,  middle  anil 
internal,  (ils.  oi'.i. 

I  e,  it  ill  II.  .    If,.  10,. 
l,4>^UIIlill4>.  S  .. 

!<«>iiM.  <-rysiallinc.  .",'JH.  .VJ3,  "rJl.  -Ml. 

developmenl  of,  or,'.). 

!.4'll4'ill4'.    107. 

Lieberktthn,  follicles  of.  is-.». 

l,iu;iiii<>ii  t.  of  the  ova! 

l.i-  .iiiK-nl.  bi-iiad.  Of  the  uterus, 

round,  of  the  uterus,  i 

round,  of  the  liver,  0%. 
l.i-lil.  perception  ot. 

destruction  of  retinal  red  by. 
l.inibs.  development  of,  007,  071. 


INDEX. 


715 


I, i mo  carbonate.  11. 
Lime  phosphate,  •"•*. 

quantity  of,  in  the  body,  38. 

in  the  tissues  and  fluids,  39. 

condition  and  uses  of,  39. 

source  and  excretion  of,  40. 

in  the  urine,  :;::<). 

deposits  of.  ;;:;t;. 
Lime  sa  1  ts.  secretion  ofby  fowl's  oviduct,589. 

absorption  of,   by  allaiitois,  from  the  egg- 
shell. (111. 

Li  110  of  direct  vision,  538. 
Lingual  nerve,  4(1:;. 
Liver,  174. 

secretion  of.  177. 

nerves  of,  is;:. 

development  of,  675. 
Liver  cells,  (is. 
Lobules,  glandular,  141. 

<>f  parotid.  141. 

of  liver,  174. 

of  lungs,  'Jo.'). 

Localization,  of  function,  in  cerebral  hemi- 
spheres, 4'26,  430.  ' 

Locomotion,  influence  of  spinal  cord  on, 
406. 

mechanism  of,  in  different  animals,  439. 
Locomotor  ataxia,  408. 
Longitudinal  fissures,  of  the  brain  and 

spinal  cord,  formation  of,  669. 
Lumbar  enlargement,  of  spinal  cord,  375. 
I. H  n us.  234. 

cooling  of  blood  in,  266. 

nerves  of,  483. 

condition  of.  after  section  of  pneumogastric 
nerves.  IM. 

development  of,  675. 
Lymph,  200.  307. 

physical  characters  and  composition  of,  318. 

movement  of.  in  lymphatic  vessels,  320. 
Lymph  and  chyle.  318. 

comparative  analyses  of,  320. 

daily  quantity  of,  321. 
Lymph  corpuscles,  196,  309-320. 
Lymph  paths.  310. 
Lym  p  ha  tic  g  la  ii<ls,309. 
Lymphatic  lacunae,  308. 
Lymphatic  system,  307. 
Lymphatic  vessels.  307. 

of  small  intestine,  196,  200. 

origin  and  course  of,  308. 

valves  of,  321. 

Macula  auditiva,  560. 
Macula  In  tea.  531. 
Magnesium  phosphate.  41. 
Mascots,  reproduction  of,  572. 
Mule  organs  of  generation,  592. 

development  of,  682. 
Malleus.  555. 
Mastication.  140. 

unilateral.  145. 

effect  of,  on  secretion  of  saliva,  145. 

muscles  of,  464. 

disturbance  of,  in  facial  paralysis,  472. 

connection  of  hypoglossal  nerve  with,  495. 
Measly  pork,  574. 
Meat,  126. 
Mecoiiinm.  674. 
Medulla  oblongata,  376,  377,  385,  439. 

gray  substance  of,  140. 

physiological  properties  of.  440. 

action  of,  as  a  nervous  centre.  440. 

influence  of,  on  respiration,  440. 

on  deglutition,  443. 

on  the  voice  and  articulation,  444. 
Medullary  canal.  620,  631,  667. 

gray  substance  of,  378. 

Medullary  fibres,  of  the  brain.  420.  421. 
Medullary  groove.  020.  <wo.  667. 
Medullary  layer,  of  nerve  fibres,  344,  345. 
Melanine.  98. 
Mem  bran  a  basilaris.  563. 
Membrana  grannlosa.  6u2. 
Membrana  tympani.  554. 
Membrane,  germinal,  618. 
Membrane,  pupillary,  669. 


Membrane,  vesicular,  of  the  Graafian  folli- 
cle. 601. 

Memory,  425. 

Meiiobraiichus,  gills  of,  233. 
.Menses.  604. 

suspension  of,  during  pregnancy,  604. 
Menstrual  periods,  (in I. 
Menstruation.  (><M. 

without  ovulation,  607. 

corpus  luteum  of,  608. 
Meseiiteric  glands,  200. 
Mesoderm.  62*. 
Micromillimetre,  51. 
Microphyte,  584. 
Middle  ear,  554. 
Milk.  123. 

globules  of,  67,  124. 

acid  fermentation  of,  124. 
Milk  sugar,  58. 
Millimetre,  51. 
Mineral  matters,  in  the  blood  plasma,  223. 

daily  discharge  of,  120. 
Motion,  channels  for,  in  spinal  nerve  roots, 

in  spinal  cord,  394. 

centres  of.  in  brain,  427. 

Motor  centres,  in  the  cerebral  hemispheres, 
427,  428. 

extirpation  of,  429. 

disease  of,  in  man.  430. 
Motor  tracts,  in  spinal  cord,  394. 

decussation  of,  397. 

Mouth,  formation  of,  in  the  embryo,  621. 
Movements,  of  respiration,  236,  238. 

of  the'heart,  277. 

of  the  limbs  from  galvanizing  brain  cortex, 
426,  427. 

of  bacteria.  78,  581. 

of  spermatozoa,  594. 

of  the  iris,  450,  457. 

Movements,  peristaltic,  of  the  oesophagus, 
150,  443,  487. 

of  the  stomach,  162, 163. 

of  the  intestine,  197. 

of  the  oviduct,  588. 
Mu cine,  88. 

usefulness  of,  89. 

in  saliva,  143. 
Mucus,  88. 

in  the  urine,  338. 

of  cervix  uteri,  591. 

Mucous  membrane,  of  the  alimentary 
canal.  137. 

of  the  stomach,  151. 

of  the  intestine,  188, 195. 

of  the  lungs,  235. 

of  the  uterus,  650. 
Muscles,  irritability  of,  361. 

termination  of  nerves  in.  350,  351,  352. 
Muscular  fibres,  of  the  uterus,  664. 

after  parturition,  665. 

Musical  sounds,  production  and  percep- 
tion of.  567. 

My  el  i  lie,  of  nerve  fibres,  344. 
Myeline  forms,  105. 
Myopia.  545. 
Myosine,  83. 

Nails,  development  of.  671. 
Near-sighted  eye,  545. 

Negative  images,  of  visible  objects,  553. 
Nerve,  olfactory.  448,  517. 

optic,  449,  519.  528. 

oculomotorius.  455. 

patheticus,  457. 

trigeminus,  459. 

alxlucens,  467. 

facial,  468. 

lingual,  463. 

great  superficial  petrosal.  475. 

small  superficial  petrosal,  475. 

of  Jacobson,  479. 

superior  laryngeal,  482. 

inferior  laryngeal,  482. 

auditory,  477. 

glosso-pharyngeal,  479. 

pneumogastric,  482. 


716 


INDEX. 


Nerve,  spinal  accessory,  490. 


sympathetic.  488. 
Nerve  cells),  356. 

in  anterior  horns  of  spinal  cord.  '•'. 

in  posterior  columns  of  >pinul  c»nl.  :'>v_. 

in  the  columns  of  riar'-s' 

in  the  cortex  of  tin-  brain  cerebral  hemi- 

vphero.  41*.  42'.). 
in  the  cerebellum.  >::'.. 
in  spinal  JUKI  sympathetic  ganglia. 

sheath  of.  :'».">  7. 

prooec 

coiinectioii  of.  with   nerve  fibre-. 

hip.)hir,  35H. 

physiological  propertied  of, 
Nerve  lib  res.  :;>:;. 

structure  of.  :;»4. 

medullated,  344. 

non-medullated.  :146. 

course  ami  mutual  relation  of,  347. 

division  of.  849. 

peripheral  tenninaiimi  of.  :;ix. 

in  the  Integument,  :'.r.». 

in  Pacinian  bodie- 

in  end  bulbs  of  the  conjunctiva,  I'-A  :]:,]. 

in  muscles,  ;;.MI,  :;:,].  :;.Y'." 

physiological  propertied  of,  351. 

motor  and  :-cnHtive,  :;.~>2,  364. 

degeneration    and  regeneration  of,  after 
division. 

connection  of,  with  nerve  cells.  367,  858,884. 
Nerve  force.  transmission  of.  :;c,r,. 
Nerve  roots,  spinal,  connection  of,  with 
spinal  cord,  384. 

excitability  of.  :;s7. 

sensibility  of,  388. 

effects  of  dividing,  387.  388. 

degeneration  of,  after  section,  389,  390. 
Nerve**,  structure  of,  :'>17. 

division  and  im»culation  of,  347. 
Nerves,  cranial,  1  16. 

classification  of,  1  17. 
Nerves.  ciliary  4H7. 
Nerve**,  spinal,  374. 

origin  of,  :;M. 

transmission  of  motor  and  sensitive  im- 

pulses in,  365,  366.  387. 
Nerves,  of  special  sense,  447. 
Nerves.  sympathetic,  r.'-. 

vaso-niotor,  ."HXJ. 

dilator,  606. 
Nervous  centre.  definition  of,  359. 

physiological  action  of.  359. 
Nervous  irritability.  360. 
Nervous  system.  29.  342. 

general  structure  and  functions  of.  I1,  12. 

white  and  gray  substance  of,  :;i:;. 

reilex  action  of, 

general  arrangement  of,  373. 

cerebro-spinal.  :;7::. 

sympathetic,  I'.'ti. 

dcvclopineiit  of,  titi". 
N<  (xvoi  k.  capillary,  299,  300. 
Neiiri  lemma.  ::i7.' 
\  i«-l  ilat  iii^  iiK'iiilirane.  500. 
Nliilli  «  i  anial  IHTVI-.  47l». 

Nitroiceii.  in  organic  substanceB,  9 

daily  consumption  of,  l:;j. 

in  the  atmosphere,  i'iu. 

Indifference  of.  in  respiration.  _'JI. 
N  i(ro-<  ii«»nv  01  -:nii<    iiia(l<-rs.     ;    7: 

in  the  food,  !•_••_'.  i:;n,  i::j. 
>'oii-iiilr4»^4-iioiis          or^-anir         suli- 

StaiKM'S.    I'.l. 

in  tin-  foo.l.  l-jo. 
<laily  consuni|>tion  of.  i:;o.  ]:vj. 
Insuffldenl  for  nutrition,  li'l. 
Niieleiiw.  oculomotorlufl  and  j)athcticiiv  166. 
trijrcniinal.  I.".1.'. 
abducciis  and  facial    >ii7,  H.s 
auditory.  477.  17s. 

glOMO-pnaryngeal,  t7'.i. 
pnenmoganric, 

spinal  aci  •• 
hypoLilo->al    I'.'.': 


Nucleus,  olivary,  493. 

of  the  impregnated  egg,  616. 
Nutrition,  functions  of,  29,  136. 

Obliteration,  of  ductus  arteriosus,  698. 

of  ductus  veiiosn.-.  i',:i7. 
of  fni-ainen  ovale.  703. 
O<-iiloiiioloi-iiis  nerve,  455. 

origin  of.  -1-V). 
decii.-sation  of.  •!">('). 

physiological  properties  of,  -irid. 

influence  of.  on  movements  of  eyeball  and 
eyelids  l.'.r,. 

on  "iris  and  pupil.  •!."./. 
<i:<sopliai:iis.  187. 

peristaltic  movements  of,  150,  443,  487. 

nerves  of. 

paralysis  of.  after  section  of  pneumogastric 

nerves,  1^7. 
<Est  mat  ioii,603. 
Oleaginous  substances.  61. 

in  the  food.  6± 

in  tJie  cliyle  C.7,  1<>7. 

in  the  blood.  •_'•_';{. 

digestion  of.  171. 

absorption  of,  197. 
Oleiiie,  64. 
Olfactory  bulb.  448. 
Olfactory  ^aii^-lia,  375. 
Olfactory  lobe,  448. 
Olfactory  nerves.  148,  517. 

physiological  properties  of,  448. 

congenital  absence  of,  449. 

effect  of  removing.  1 19. 
Olfactory  tracts.  448. 
Olivary  bodies.  ::77. 

connection  of,  with  hypoglossal  nerves, 

493. 

Opcrciilmn.414. 
Ophthalmic  ganglion,  457. 
Oph  t  ha  I  moscope,  ~>u~>. 
Optic  ganglia.  :'•<<<. 
Optic  nerves.  II1.). 

decussation  of,  :',77.  419,  451,  45J,  4 :•:'..  454. 

central  origin-  of,  4 •")(). 

]ihysiol<igieal  properties  of,  4. ""•<>.  :.js. 

development  of.  669. 

Optic  nerves  and  tracts.  ".77,  451.4f>:>  4.M. 
Optic  thalami.  376,  417. 
Optic  tracts.  II'.). 
Optograms.  >:,»>. 
Ora.  serrata,  526. 

Orbital  muscle,  in  quadrupeds,  500. 
Organ  of  <  orli.  :>f>4. 
Organic  matter,  production  of  by  plants, 

I'.i,  C.:;,  7'.). 

Os  exteriiiim.  of  the  uterus,  .v.u. 
Os  intern  mil.  of  the  uterus,  .v.M. 
4»seillalori:e. 

Ossicles,  of  the  middle  ear,  554. 
Ossification,  in. 

of  skeleton,  in  the  chick,  644. 

in  the  human  io'tus.  t'>7n. 
Osteomalakia.  in. 
Otic  ganglion.  47."..  l!»7. 
Of oconia.  "'tin. 
Ovarian  |»regnaney,  606. 
Ovaries.  582-586. 

])hysinlogical  action  of,  :.!);>. 

quiescence  of,  during  pregnancy,  612,  614. 

development  of,  • 

descent  of,  685. 

condition  of,  at  birth,  686. 
Oviducts. 

physiological  action  Ol 
0\iil:ilion.  699. 

iii  menstruation 

suspended  during  pregnancy,  613,  614. 
Ovum 

Oxalic  acid,  in  fermenting  urine.  339. 
Oxidation,  of  starch,  fat,  and  albumen. oxy- 
•4cu  required  for,  131. 

of  March.  1 

of   I:    ' 

of  albumen.  KM. 
of  tartaricacid 
Ov>  K-en,  .Ahaled  in  vegetation,  50. 


INDEX. 


717 


Oxygen,  necessary  for  putrefaction,  77. 

action  of,  on  hemoglobine,  94. 

daily  consumption  of,  in  the  food,  132. 

absorption  of,  in  respiration,  232.  '240. 

proportion  of,  to  carbonic  acid  exhaled,  218. 

effect  of,  on  the  color  of  the  blood,  252. 

quantity  of,  in  arterial  and  venous  blood, 253. 

absorption  of,  by  the  tissues,  253. 

by  the  fowl's  egg,  in  incubation,  644. 
Ox y hemoglobine,  94,  95. 
Oxynris  vermicularis,  573. 

Paciniaii  bodies,  349. 

termination  of  nerves  in,  350. 
Painful  impressions,  transmission  of,  in 

spinal  cord,  371. 
Palate,  formation  of,  679. 

fissure  of,  680. 
Palmitiiie,  64. 
Pancreas,  165. 166. 

secretion  of.  165. 

nerves  of,  499. 

Pancreatic  ferments,  86, 168. 
Pancreatic  fistula,  166. 
Pancreatic  juice,  165. 

physical  properties  and  composition  of,  167. 

secretion  and  daily  quantity  of,  170. 

physiological  action  of,  171. 
Pancreatine,  86,  168. 
Papilla,  of  the  retina,  526. 
Papillae,  lingual,  514. 
Par  vagum.  is- 
Paras  lobnline.  81. 

in  blood-plasma,  222. 
Paralysis,  various  forms  of,  400. 

facial,  471. 

from  cerebral  lesion,  4ol,  429,  4:50.  4:j:!,  4'.i:;. 

of  tongue  from  disease  of  medulla  oblou- 
gata,  445. 

of  glottis,  after  section  of  pneumogastric 
nerve,  485,  492. 

of  oesophagus  and  stomach,  after  section 
of  pneumogastric  nerve,  487,  488. 

of  glottis,  after  evulsion  of  spinal  accessory 

nerve,  492. 
Paraplegia,  400. 

reflex  action  of  spinal  cord  in,  405. 
Parasites,  internal,  573. 
Parotid  gland,  141. 
Parotid  saliva,  144. 
Parotid  plexns,  of  facial  nerve,  468. 
Parturition,  663. 

arrest  of  hemorrhage  in,  663,  664. 
Patheticus  nerve.  457. 

origin  of,  458. 

physiological  properties  of.  458. 
Peduncles,  of  the  brain,  378. 
Peduncles,  of  the  cerebellum,  anterior,  378. 

inferior,  377.  386. 

middle,  378. 
Pepsi  ne,  84,  86. 

in  gastric  juice,  156. 

production  of,  157. 
Pepsin e  extracts,  158. 
Peptone.  84. 

diffusibility  of,  75,  84,  159. 

produced  in  digestion,  159. 

contained  in  blood-plasma,  223. 
Perception,  visual,  general  laws  of,  549. 
Peri  lymph.  55'.). 

Peristaltic  action,  of  the  oesophagus,  150, 
443,  487. 

of  the  stomach,  162.  163. 

of  the  intestine,  197. 

of  the  oviduct,  588. 
Peritoneal  cavity,  formation  of,  in  the 

embryo,  636. 
Perosmic  acid,  action  of,  on  medullary 

layer  of  nerve  fibres,  344,  345. 
Persistence,  of  luminous  impressions,  549. 

of  sonorous  impressions,  507. 
Personal  error.  371. 

variation  of,  372. 
Personal  equation.  372. 
Perspiration,  cutaneous,  272. 
Pes  aiiserinus,  468. 


Petrosal  ganglion.  479. 

Petrosal  nerve,  great  superficial,  475. 

small  superficial,  475. 

Pctteiikoter's    test    for    the    biliary 
salts.  110. 

spectrum  of,  111. 

!  Peyer's  patches,  in  small  intestine,  196. 
I  Pharynx,  137. 

action  of,  in  swallowing,  481,  487. 

nerves  of,  479,  482.  487. 

development  of,  677. 
Phenomena,  of  living  beings,  general  and 

special,  27. 
Phoiiatioit,  444. 

connection  of  medulla  oblongata  with,  444. 

of  pneumogastric  nerve,  486. 

of  spinal  accessory,  491. 
Phosphate,  lime,  38. 

magnesium,  41. 

sodium.  44. 

aminonio-magnesian,  340. 
Phosphates,  alkaline,  44.  45,  330. 
Phosphates,  earthy,  41,  330. 

deposits  of,  in  the  urine,  336. 
Phospho-glyceric  acid,  105. 
Phosphor! zed  fat.  105. 
Phosphorus,  in  lecithine,  45, 106. 

oxidation  of,  in  the  body,  46, 106. 
Physiological  chemistry,  28,  30. 
Physiology,  definition  of,  25. 

modern  study  of,  26. 

different  departments  of,  28. 
Placenta.  655. 

development  of,  657. 

blood-vessels  of,  658. 

function  of,  659. 

separation  and  discharge  of,  661. 
Placeiital  circulation,  688. 
Plasma,  of  the  blood,  221. 
Plasm i lie.  227. 
Plates,  dorsal,  of  the  blastoderm,  620,  630. 

abdominal.  620. 
Plexns.  capillary,  299,  300. 

lymphatic,  308. 

terminal,  of  nerves,  348. 

parotid,  468. 

laryngeal,  482. 

pulmonary,  483. 

(jesophageal,  483. 

solar.  498. 
Pneumogastric  nerve,  482. 

origin  and  branches  of,  482. 

physiological  properties  of,  483. 

connection  of,  with  respiration,  484. 

with  the  voice,  486. 

with  deglutition,  487. 

with  stomach  digestion,  488. 

with  the  heart's  action,  489. 
Point  of  distinct  vision,  531. 
Point  of  fixation,  in  binocnlar  vision,  547. 
Polarized  light,  rotation  of,  53. 

by  dextrine,  53. 

by  glucose.  55. 

by  lactose,  58. 

by  saccharose.  59. 

by  glycogen.  60. 

by  cholesterine,  71. 

by  albumenoid  substances,  74. 

by  albumen,  80. 

by  the  biliary  salts,  109. 
Pollen.  582. 
Pons  Tarolii.  377.  435. 
Portal  vein,  distribution  of,  in  the  liver,  174, 
175, 

development  of,  695. 

Posterior    columns    of    the    spinal 
cord,  375,  377,  384. 

sensibility  of,  391. 

effect  of  dividing.  393.  407. 

influence  of,  on  the  attitude  and  locomo- 
tion. 407. 

ascending  degenerations  of,  407,  408. 

locomotor  ataxia,  from  sclerosis  of,  408. 
Posterior  pyramids,  of  medulla  oblou- 

gata,  408. 
Potassium,  carbonate,  46. 

chloride,  43, 


718 


IXDEX. 


Potassium,  phosphate,  n. 

biphosphate.  1 ... 
sulphate,  17. 
Pregnancy,  influence  of,  on  the  exhalation 

of  carbonic  acid,  24:;. 
suspension  of  me  use-  in.  ''>"1. 
ovarian   < 

abdominal,  606. 

tubal.  tun;. 

growth  of  uterine  m  in 'ous  mem branein.r.,.0. 

Pressure,  of  the  bloo.l,  in  auricle-  and  veii- 
tricl. 

in  the  arteries.  2'.»2. 
Primitive  furrow.  »',27. 
Primitive  trace.  619,  ttt1..  r.27. 
Prota^oii.  in., 
Protovertcbra'.  r, :;:;. 

transformation  and  disappearance  of,  ('<;'•[. 

Ptosi*. 
I'l.valine.  85. 

in  saliva.  1  C'.. 
Puberty.t,oo 
Piilsati«»n.  of  the  heart.  277,  288. 

of  the  artel  ie- 
Pulse,  arterial.  2*;.  2*7. 

traces  of,  2*'.',  2'.K).  2'.M. 
Pulse,  dierotic.  2<». 
Fuplll  520, 521, 522, 

sphincter  ami  «lilator  muscles  of,  .VJ2. 

movements  of.  l.".o. 

dilatation  of.  alter  division  of  oculo-mo- 
torius  nerve,  l.",7,  !'.»»'>,  I'.*',). 

contraction  of,  alter  section  of  sympathetic 

nerve.  I'.i'.i. 

Pupillary  membrane,  in  the  fuutus,  669. 
Pus,  in  the  urine.  338. 
Putrefaction.  76. 

conditions  of,  77. 
Pyramids,  anterior,  397. 

deeiissation  ot. 
Pyramids,  posterior,  408. 
Pyramidal  cells,  in  cortex  of  brain,  418. 

giant,  419, 429. 

Pyramidal   tracts,  in  brain  and   spinal 
cord,  395. 

Quantity,  daily,  of  air  used  in  respiration, 

239. 

of  the  food,  12!». 
of  bile,  182. 
ofbiliaryaci.ls.llO. 
of  carbonic  acid  exhaled,  212. 
of  creatiniue.  1 1 1. 

of  eartby  posphatcs  in  the  urine.  11. 
of  feces,  194. 

of  fluids  secreted  and  reabeorbed,  :;2;;. 
of  gastric  juice,  161. 

Of  Dme phosphate,  in  the  urine,  10. 
of  lymph  and  chyle,  :!J1. 
of  magnesium  phosphate,  in  the  urine,  II. 
of  mineral    matter    introduced    and    dis- 
charged, 120. 

of  oxygen  consumed.  2 in. 
of  pancreatic  juice,  170. 
of  perspiration,  272. 

of  saliva,  n:.. 

of  sodium  chloride  discharged.  I::. 

of  sodium   and  potassium  phosphate-,  in 

the  urine,  I*',. 

of  sodium  and  potassium  sulphates,  in  the 
urine.  47. 

lid  matters,  in  the  urine,  :!2t'.. 
of  urea.  1 1",. 
of  urine. 

Quantity,  entire,  of  Mood  in  the  body,  2::o. 
of  iron  in  the  bloo.l,  -.17. 
of  lime  phosphate  in  the  bo.; 

•iium  chloride  in  the  body,  II. 
of  sulphur  in  the  albuminoiis'ingredients 

of  the  body.  47. 
<tuiiiiiic,  elimination  of,  by  the  urine. 


llato  of  transmission,  in  sensitive  nerves, 
869. 

in  spinal  cord.  :!7u. 
in  tlie  brain,  ;!71. 


K.M  luiix    in. 

Italoot  Iraiismissioii.ot  nerve  for. 

methods  of  determining,  307. 
in  motor  aerve 


|{<  «  Him.  ]:,7. 

evacuation  of,  409,410. 
Ro«l  slolmlos.  of  the  blood,  'Jl-J. 

structure  of,  L'l  I. 

composition  of.  'Jif>. 

physiological  function  of.  -Jilt. 

absorption  of  oxygen  by,  •_'!'.»,  '2'A, 
Rod.  retinal,  :.::!. 

BefleetiOB,  images  of,  in  the  eye.  .'41. 
lO-Ilcv  a<*tii»ii.  of  the  nervon>  system,  359. 

of  the  spinal  cord.  -lol. 

of  the  medulla  oblongata,  -1  -!_•_',  11:'.. 

for  movements  of  the  iris,  1  .'.;>. 

for  tlie  movements  of  winking,  473,  474. 

for  the  movements  of  respiration,  is">. 
Reilcx     contraction    and    dilatation    of 

blood-vessels,  JV)7. 

Refraction,  by  the  crystalline  lens..Vj:;.  .Vjl. 
Res'«?"«'ration.  of  divided  nerve  libro,  855. 

of    the  uterine    mucous    membrane  and 

muscular  tissue,  in  pregnancy,  tir.i. 
CCcu'istcriiiU'  apparatus,  of  Marey,  368. 
Rcil,  island  of,  114,417,433. 
Rennet.  1JI. 
ilcprodiictioii,  29,  569. 

nature  of,  fn;;i. 

by  generation,  570. 

of  maggots,  r>72. 

of  entozoa,  573. 

of  cystieercus  eellnlosie,  575. 

of  trichina  BpiraUs,576. 

of  infusoria.  .".T'.t. 

oviparous  and  viviparous,  .v.i'.i. 
Resinous  matters  of  the  bile,  108. 
Respiration.  j:J± 

organs  of,  233. 

aquatic.  2:  '.:'.. 

aerial,  234. 

movements  of,  -j:;t;. 

abdominal,  287. 

thoracic,  2:;7. 

nii>i<lity  of,  •_':'.'.». 

((iiantity  of  air  used  in.  2:  '.7,  2:  •!'.). 

nature  of,  256. 

relation  of,  to  heat  production,  2fi:-. 

nervous  centre  of,  in  medulla  oblongata, 
ill. 

influence  of  pncnmogastric  nerve  • 

reflex  action  of,  485, 

suspension  of,  in  deglutition,  488. 

in  muscular  ellort.  492. 
Restitorm  bodies. 
Retina,  520,626. 

layers  of,  526,  ;vj7,  .vjs. 

ganglionic  cells  of.  .vj~. 

rods  and  cones  of.  :>27,  .Vjs. 

reception  of  luminous  impressions  by,  528, 

development  of,  <'''•'.'. 
Retinal  red.  f>:u. 

destroyeil  by  the  action  of  light, 

reproduction  of,  during  life. 
Rhythm,  of  the  heart's  action,  'JMI. 
Rods  and  cones,  of  the  retina.  ,VJ7. 
Rotation,  of  the  ]>lane  of  polarisation,  for 

polari/ed  light,  .>:!. 
R<»tatory  power,  of  dextrn 

of  glucose 

of  lactoM 

of  sacchar 

of  glycogen,  60. 

of  cholesterine,  71. 

of  albumenoid  Mibstnnces,  <  1. 

of  albumen,  so. 

of  the  liiliary  sal' 
Round  ligament,  of  the  uteru^. 

of  the  liver.  r.'.M1,. 

Itiimiiiat  ion.  secretion  of  saliva  in,  1  !•>. 
ICn  1  1  inu  season,  •'>".'.. 

Sa<'chariii<>  siil»stane<>s.   >1. 
Sac<-haromyees  <*erevisiae,  57, 

in  fermentation 


INDEX. 


719 


Saccharose,  59. 

Sacculus.  of  the  internal  ear,  559. 
Saliva,  141. 

physical   properties  and  composition  of, 
142. 

action  of,  on  starch,  143. 

varieties  of,  144. 

daily  quantity  of,  145. 

physiological  action  of,  140. 

as  auxiliary  to  the  sense  of  taste,  516. 
Salivary  glands,  141. 
Sal  is.  biliary,  108. 

of  the  blood,  223. 

of  the  urine,  329. 
Sapoiiification,  04. 
Scala  tympaiii,  503. 
Scala  vestibuli.  >t»:j. 
Schlemnt,  canal  of,  520. 
Sclerosis,  of  posterior  columns  of  spinal 

cord,  408. 

Sclerotic  coat,  of  the  eyeball,  519,  520. 
Sebaceous  matter,  of  the  skin,  71. 

in  the  fetus,  671. 

Second  pair  of  cranial  nerves,  449. 
Secretion,  of  saliva,  144. 

of  gastric  juice,  153. 

of  pancreatic  juice,  170. 

of  bile,  180. 

of  albuminous  matter  by  the  oviducts  and 
Fallopian  tubes,  587,  588,  617. 

of  calcareous  matter  by  the  oviduct,  589. 
Segmentation,  of  the  vitellus,  617. 

in  the  fowl's  egg,  624. 
Self-digestion,  of  stomach,  160. 

of  pancreas,  169. 
Semicircular  canals,  559. 

office  of,  561. 

effects  of  iniury  to,  562. 
Seminal  fluid,  582. 
Seminiferous  tubes,  594. 
Sensation.  510. 

of  pain,  512. 

of  temperature,  512. 

channels  for,  in  spinal  nerve  roots,  388. 

in  spinal  cord,  393. 

centres  of,  in  the  cerebral  hemispheres,  430. 
Sense,  of  touch,  510. 

of  taste.  513. 

of  smell,  517. 

of  sight,  519. 

of  hearing,  554. 

organs  of,  development  of.  007. 

special,  nerves  of,  '117. 
Senses,  the,  510. 

mode  of  action  of,  513. 
Sensibility,  general,  510. 

delicacy  of,  in  different  regions,  511. 

tactile,  510. 

of  the  tongue,  403. 
Serum,  of  coagulated  blood,  225. 
Seventeen-year  locust,  572. 
Seventh  cranial  nerve,  408. 
Sexes,  male  and  female,  582. 
Sexual  generation,  582. 
Sexual  organs,  male,  594. 

female,  585. 

development  of,  683.  685. 
Sheath,  lamellated,  of  nerves,  347. 

tubular,  of  nerve  iibres,  344. 

of  Henle,  348, 

of  Schwann,  344. 
Shock,  nervous,  362. 
Sight,  sense  of,  519. 

organ  of,  519. 

physiological  conditions  of,  537. 

influence  of  trigeminus  nerve  on,  466. 
Single  vision,  with  two  eyes,  547. 
Sinuses,  vascular,  of  the  placenta,  657,  658. 
Sixth  cranial  nerve,  467. 
Skeleton,  mass  and  composition  of,  38. 

ossification  of,  39,  40,  644. 
Skin,  sebaceous  matter  of.  71. 

watery  secretion  of.  38,  272. 

development  of,  671. 
Smell,  sense  of.  517. 

nerves  of,  448,  517. 

necessary  conditions  of,  518. 


Smell,  acuteness  of,  in  animals,  519. 

influence  of  trigeminus  nerve  on,  465. 
Sodium  carbonate,  46. 
Sodium  chloride,  41. 

proportion  of,  in  the  tissues  and  fluids,  42. 

in  the  food,  42. 

usefulness  of,  -12. 

discharge  of,  -13. 

in  the  urine,  330. 
Sodium  glycocholate  and  taurocho* 

late.  108,  109,  179,  334. 
Sodium  hippurate,  118. 
Sodium  phosphate,  44. 

biphosphate,  45. 

in  the  urine,  329. 
Sodium  sulphate,  47. 
Sodium  u  rate,  117,  329. 
Solar  plexus,  498. 
Solidity  and  projection,  appreciation 

of,  in  binocular  vision,  548. 
Sonorous   impressions,  persistence  of, 

567. 

Sound,  sensation  of,  554. 
Sounds,  of  the  heart,  277. 

musical,  production  and  perception  of,  567. 
Special  sense,  nerves  of,  447. 
Species,  definition  of,  570. 
Specific  gravity,  of  saliva,  142. 

of  gastric  juice,  154. 

of  bile,  177. 

of  intestinal  juice,  190. 

of  blood,  212. 

of  blood  globules,  212. 

of  blood  plasma,  212. 

of  lymph,  318. 

of  urine,  325. 
Spectrum,  of  hemoglobine,  94. 

of  biliverdine,  100. 

of  urobiline,  102. 

of  chlorophylle,  103. 

of  Pettenkofer's  test,  111. 
Sperm.  r>82. 

Spermatic  fluid,  582,  592. 
Spermatozoa,  592,  593. 

movements  of,  592. 

formation  and  discharge  of,  594. 

fecundation  by,  595. 

entrance  of,  into  egg,  596,  016. 
Spheno-palatine  ganglion,  475,  497,518. 
Spheres,  vitelline,  618. 
Sphincter  ani,  action  of,  409. 

muscles,  influence  of  spinal  cord  on,  409. 

pupillae,  522. 

vesicse,  410. 

resistance  of,  to  pressure,  411. 


Sphygmog-raph,  289. 
Spiiiabefida.  670. 


Spinal  accessory  nerve,  490. 

branches  and  distribution  of,  491. 

motor  properties  of,  491. 
Spinal  column,  development  of,  633,  670. 
Spinal  corcl,  374,  381. 

gray  substance  of,  374. 

white  substance  of,  375. 

columns  of,  375. 

arrangement  of  gray  and  white  substance 
in,  381. 

transverse  sections  of,  374,  382,  383,  396,  408. 

connections  of.  with  brain,  385. 

transmission  of  motor  and  sensitive  im- 
pulses in,  370,  387,  390,  392. 

sensitive  and  excitable  parts  of,  391. 

channels  for  sensation  and  motion  in,  392. 

crossed  action  of,  397. 

reflex  action  of,  401. 

physiological  action  of,  as  a  nervous  centre, 
405. 

origin  of  vaso-motor  nerves  in,  504. 

development  of,  667. 
Spinal  nerves,  origin  of,  374,  S81. 

transmission  of  motor  and  sensitive  im- 
pulses in.  365,  366,  387. 

degeneration  of,  after  division,  353, 389, 390. 
Spiral  ganglion,  of  the  cochlear  nerve,  565. 
Spiral  lamina,  of  the  cochlea,  563. 
Spleen,  nerves  of,  499. 
Spontaneous  generation,  572. 


720 


INDEX. 


Npot  embryonic,  •'.l-. 
Stapedius  muscle, 


Slar«  I. 

production  of,  in  planl 

ci-mposiiiiiii  i.t'.  t'.t. 
quantity  of,  in  f<ni«l.  .")'_'. 

transformation  of.  into  dextrine,  •>:'>. 
into  Mi-jar.  ."•:;.  1  !•'•. 
di-eMion  of.  172. 

SI  <i  roll  c«in  2  ^  -alciit.  of  fatty  substances,  131. 
Star<  li  grains.  51. 
St«-ari«-  a«-i«i.  > 
Stearin*-.  61. 

sai  .....  ifirution  • 
Sl<  r«  OH<  op«-.     I'1. 
Sloma*  h.  [87, 

mucous  membrane  »f,  r>i. 

-:ric  juice  hv 

liMlll:. 

self  dk-vstion  (,f,  160. 

process  (lf  digestion  in.  162. 
peristaltic  action  of.  Id:;. 

nerves  of,    I- 

Inflnenee  of  pneumogastrio  nerve  on,  488. 

irritulu'lity  ol,  in  pregnancy.  <'il2. 

development  of,  672. 

Strabismus.  external,  from  lesion  of  oculo- 

motorius  nerve. 
internal,  from  lesion  of  abducens  nerve, 

Striated  bodies.  :7...  116. 
Strvrliuiiic.  elVeet  of,  on  spinal  cord,  |u:;. 
Snbliii^iial  ii«'i-\4>.  i  hypoglossal,)  493. 
SubliiiKual  saliva.  Ml. 
Siibmaxillary  uaiiKlioii,  497. 
.Siilmia  x  1  1  1:«  r>   ^  laud.  1  12. 

vasomotor  and  dilator  nerves  of,  :>06. 

saliva,  144. 
.  54. 

quantity  of  in  dillei-ent  Mihstnnccs.  .".1. 

varieties  of.  :.l. 

tecti  i 

fermentation  of.  57. 

production  of,  from  starcli,  ~>:\. 

from  glyoogen,  <>i. 

in  the  li\«  i 

detection  of.  in  the  urii  •• 

internal  production  of,  in  the  l«etn>.  C>7.~>. 
Sul|»liat<>s.  sodium  and  potassium,  17. 

in  the  urine,  :;:;i. 

Siil|»lio<-.>  aii4»^4-ii.  in  saliva,  1  i:',. 
Sulphur,  in  albuminous  matters.  -17. 
iu.  I!:;.  1  1  1,  !M,  1M,  I'.-... 
1  1«    -au^li.t  and  norvcN.  l'.»s. 

f  ii«'ii<-  n«>r%«>.  Influence  of,  on  tlie 

ocal  circulation,  "lOL*. 
S>  iui»atli«>(i«*  s^sieiu.  general   arrangu- 

llH'Ilt    Of, 

ganglia  and  nerve-  of 
diMril.ution  of.  \\>7.  -Jus.  \w. 
sensibility  and  motor  power  in,  1'.''.'. 
connection  of,  \\  itii  sp  .  I(JD. 

\\ith  the  circulation. 
.S.yiitoniii. 

produced  in  stomach  di-.-Mion,  lo'J, 

I  n<  Ml.   s«>i.sil»ility,  510. 

in  the  skin,  .Ml. 

ofthetongnt 
Tadpoi*'.  development  of.  «',-ji. 

tran>tnrmation  of.  ini 
Ta-uia  soliiim. 
I  >ip<  uorui.  rejiroductioii  ot 
Tarlarl<-  acid.  "\id;ition  of,  250. 
eof,  r,i:;. 

n-iniisite  conditions  of,  .M">. 

locali/ation  of,  in  ti.n^ue  and  fa" 

in  11  u-  -uce  nf  tri'.:i-ijiiniis  :ic!  \  e  mi,  H'«t'.. 
aMrctioiiof.  fmm  le-ion  of  cliorda  tymi.au  i. 

'.uds,  in  the  lom;i;. 


Taiirocliolatc,  M,dium.  lu-.i. 


Taurocholate  in  the  bile,  17'J. 

in  uriue,  334. 
Taurocholio  acid.  Km. 

hydration  of.  Km. 

dehydration  of.  109. 
Teeth,  action  of,  in  mastication,  no. 

condition  of,  in  newly-born  infant,  705. 

change  of,  in  second  dentition.  700. 

riiieiitum.  <ff  crura  cerebri,  4LI1. 
l'ciiii»cratnrc.  animal.  'J'.s. 

variations  of,  201. 

in  man,  •_'»;_'. 

effect  of  digestion  on,  -Jd-J. 

of  arterial  and  venous  blood,  'j*;;,. 

local  elevation  of.  'Jii7,  r.u:;. 

regulation  of,  ~2ffi. 

eft%ct  of  lowering,  269. 

effect  of  elevating,  -J7o. 

moderation  of,  by  breathing  and  perspira- 
tion, 272. 

influence  of.  on  diffusion,  :;!<>. 

sensations  of.  f>l2. 
Tensor  timpani.  •>'>'>. 

action  of,  .:>:>7. 

Ten  Hi  cranial  nerve.  482. 
Terminal  buds,  of  sensitive  nerve  fibres, 

860. 
Termination,  peripheral,  of  nerve  fibres, 

848. 
Tests,  for  starch,  52. 

for  glucose,  55. 

for  the  biliary  salts,  110. 

for  bilirubine.  99. 

for  saccharine  urine,  333. 

for  albuminous  urine,  335. 

for  the  urates,  336. 

for  blood,  mucus,  and  pus,  in  the  urine. 

337.338. 
Testicles,  582. 

development  of,  i^J. 

descent  of,  688. 

Tetanus,  reflex  phenomena  of,  403,  40  1. 
T  ha  la  mils,  optic.  :'.7(),  417. 

development  of,  Oils. 
I'liaiimat  rop<>.  ."MM. 
Third  cranial  nerve.  I'M. 
Thoracic  duct.  201. 

respiration,  2.'i7. 
Thorax,  movements  of,  in  respiration,  2:;r>. 

development  of,  •'•"."). 
Tie  douloureux.  !•.:'-. 
Tong-iic.  oflice  of,  in  mastication,  150. 

tactile  sensibility  of,  463. 

paralysis  of.  from  disease  of  medulla  ob- 
longata,  44.">. 

from  cerebral  hemorrhage,  493. 

innervation  of,  494,  .">]  1. 

vasomotor  and  dilator  nerves  of,  r>(>6. 

as  the  organ  of  taste,  -ir.i.  f>i:;. 
Toothache,  from  affections  of  the  trigeminus 

nerve,  463. 
Touch,  sense  of,  510. 

organs  of,  511. 

Trace,  primitive,  of  the  embryo.  6U»,  626.  627. 
Tracts,  motor,  in  the  spinal  cord,  394. 

pyramidal.  :!'.»,">. 

olfactory,  HS. 

optic,  1  a. 

.  of  motor  and  sensitive  im- 


pulses, in  the  spinal  cord  and  nerves,  365, 

§66,  887.  :>:>2. 
Transiidalioii  and  absorption,  by  ani- 

mal tissues.  :;io. 
Trichina  spiral!*.  ">7l. 

reproduction  of,  ;>76. 
Triclioecphalus  dispar 
Tricus|>id  valves,  27  .  276. 


nerve.  )>'.). 

origin  and  distribntii>n  of.  -1 
physiological  properties  of,  ItVJ. 
painful  atVecti-.ns  of.  If,;;. 
lingual  branch  of.  !''«:'>. 
motor  branches  of.  162.  |»;i. 
anastomotic  branclies  of,  46t. 
influence  of.  on  sjiecial  sensi  - 
Trominer'M  test  for  glucose,  55. 
,  87,168. 


INDEX. 


721 


Tubal  pregnancy,  606. 

Tube,  Eustachian,  558. 

Tuber  aimulare,  377. 

Tubercula  quadrigcmiiia,  376,  450. 

development  of,  668. 
Tubes,  Fallopian,  590. 

seminiferous,  594. 
Tubules,  gastric,  151. 

intestinal.  189. 

uterine,  650. 
Tufts,  of  the  chorion  and  placenta,  655,  656, 

657. 

Tunica  albugiiiea,  of  the  ovary,  590. 
Tunica  vag-inalis  testis, formation  of, 684. 
Turck.  columns  of,  395. 
Twelfth  cranial  nerve,  493. 
Tympanum  of  the  ear,  membrane  and 

chain  of  bones  of,  554,  555. 
Tyrosine,  107. 

Umbilical  arteries  and  veins,  forma- 
tion of,  690. 
Umbilical  cord,  661. 

spiral  twist  of,  662. 

separation  of,  after  birth,  705. 
Umbilical  hernia,  congenital,  674. 
Umbilical  vein,  689,  690. 
Umbilical  vesicle,  636.  640,  662,  663. 

circulation  of,  688. 
I  *  radius.  676. 
Urate.  sodium,  117. 

in  the  urine.  329. 

deposits  of,  336,  337. 
Urea,  114. 

production  of,  from  albuminous  matters, 
115. 

conversion  of,  into  ammonium  carbonate, 
115. 

daily  quantity  of,  115. 

variations  of,  under  food  and  exercise,  116, 
117,  328. 

decomposition  of,  in  fermenting  urine,  340. 
Uric  acid,  45,  117. 

relations  of,  to  urea,  food  and  exercise, 
118. 

in  the  urine,  332. 

Urinary  bladder,  innervation  and  action 
of,  410. 

paralysis  of,  411. 

development  of,  676. 
Urinary  deposits,  336. 
Urine,  334. 

physical  properties  of,  325. 

daily  quantity  of,  326. 

composition  of,  327. 

reactions  of,  331. 

alkalescence  of,  from  vegetable  food,  46. 

carbonic  acid  in,  243. 

abnormal  ingredients  of,  332. 

deposits  in,  336. 

decomposition  of,  338. 

retention  and  evacuation  of,  110. 
Urobiline,  102. 
Urochrome,  101. 
Urohematine,  102. 
Urosacine.  102. 
Urosiite,  102. 
Uroxanthine,  102. 
Uterus,  590. 

influence  of,  on  other  organs,  612. 

mucous  membrane  of,  650. 

growth  of,  in  pregnancy,  651. 

regeneration  of,  after  delivery,  664. 

development  of.  in  the  embryo,  685. 
Utricle,  of  the  internal  ear,  559. 
Uvea,  522. 

Vagus  nerve.  482. 

Valve,  Eustachian,  699. 

of  the  foramen  ovale,  701. 

of  Vieussens,  458. 
Valves,  cardiac  and  arterial,  275,  276. 

of  the  veins,  296. 

of  the  lymphatics,  321. 
Valvula?  conniventes,  development  of, 

673. 
Vapor,  organic,  in  the  breath,  245,  248. 


Vapor,  watery,  in  the  air,  240. 

in  the  breath,  245. 

Vascular  area,  in  the  incubated  egg,  635. 
Vascular  system.  274. 

development  of,  687. 
Vas  deferens.  594. 

formation  of,  684. 
Vaso-motor  nerves,  500. 

influence  of,  on  the  circulation,  502. 

origin  of,  504. 

Vegetables,  as  food,  127. 
Veins,  295. 

inter-lobular,  intra-lobular,  and  hepatic, 
174, 175. 

Vitelline,  638,  687. 

omphalo-mesenteric,  688. 

umbilical,  690. 

vertebral,  692. 

portal  and  hepatic,  formation  of,  695. 
Vena  azygos,  major  and  minor,  formation 

Vena  cava.  superior  and  inferior,  formation 

of,  692,  694. 

Vena  innominata,  formation  of,  693. 
Veil  a  terminalis,  of  the  area  vasculosa, 
636. 

disappearance  of,  687. 
Venous  system,  development  of,  692 
Ventricles,  of  the  heart,  275. 

comparative  thickness  of,  280. 

muscular  fibres  of,  281,  282. 

pressure  of  blood  in.  284,  285. 
Vermiform  appendix,  development  of, 

673. 

Vernix  caseosa,  671. 
Vertebral  arteries,  688. 
Vertebral  column,  development  of,  633, 

635. 

Vertebral  veins.  692. 
Vesicle,  germi  native,  585. 

disappearance  of,  after  impregnation,  616. 
Vesicle,  umbilical,  639,  640. 

circulation  of,  688. 

Vesicles,  cerebral,  in  the  embryo,  668. 
Vesicles,  pulmonary,  235. 
Vesicular  seminales,  594. 

.     development  of,  684. 
Vesicular  membrane,  of  the  Graafian 

follicle,  601. 

Vestibule,  of  the  internal  ear,  558. 
Villi,  of  the  intestine,  195. 

of  the  chorion,  645,  647. 
Visceral  folds,  in  the  embryo,  677,  690. 
Vision,  519. 

localization  of,  in    angular  convolution, 
439. 

disturbance  of,  from  lesion  of  optic  nerves 
and  tracts,  453. 

function  of  crystalline  lens  in,  524. 

physiological  conditions  of,  537. 
Vision,  double,  outside  the  point  of  fixation, 
547. 

from  pressure  on  the  eyeball,  548. 

from  paralysis  of  patheticus  nerve,  458. 
Visual  impressions,  550. 
Visual  perception,  general  laws  of,  549. 
Vitelline  arteries,  638. 
Vitelline  circulation.  687. 
Vitelline  membrane.  584. 
Vitelline  spheres.  6181 
Vitelline  veins,  638. 
Vitellns.  584. 

segmentation  of.  617. 

Elastic  and  nutritive,  624. 
ation  of  the  air,  by  respiration,  246. 
Vitreous  body,  of  the  eyeball,  522,  523. 

development  of,  669. 
Vocal  chords,  action  of,  in  respiration,  238. 

in  the  voice,  486. 
Vocalization.  486. 

control  of.  by  medulla  oblongata,  444. 
Voice,  formation  of,  444,  486. 

connection  of  pneumogastric  nerve  with, 

486. 

of  spinal  accessory  nerve,  491. 
Volition  and  perception  in  the  brain,  rapid- 
ity of,  371. 


2V 


722 


I  N  D  K  X  . 


Voluntary   motion,  channels  for,  in    the 
spinal  conl,:;'.U. 

%Val«T.  in  tin-  bod] 

proportion  of,  iii  tin-  tissues  and  fluids.  :;r>. 
in  the  fond,  UN 

diM-han,rc  I 

from  tin-  hums  iiml  skin,  :;*•,  _'i:>,  I'tif,,  i'7'J. 

by  tin-  kid!;- 

from  ilic  (owl's  t'ur«.  in  incubation.  <Vi:;. 
\\  <  ii;lit  of  oricaiiM.  in  the  iu>\vly-born  in 

I'uni  ami  adult.  7n:>. 
%Vln>al.  \-S>. 
\\li «•;«(«> ii  hr<»a<l.  IJi, 


sHiir.  .  of  ih<-   >pinul 
: '.71,383. 

of  the  brain,  878. 
>Vhit<>  of  ou-tt-.  MI.  1-7.  588,  r,i7. 
\Vliii«-  K-lobiil(>M.  of  the  blood.  -_>iy. 

ol'  tlie  lymph.  .'309. 
Winking,  movements  of,  -470 

reflex  action  of.  -17:5.471. 
Wolfiian  bodies,  684. 

Y«'a*».  action  of.  in  fermentation,  :>7. 
1'<>llow  N|»ol.  of  tlie  retina 
Yolk.  587. 

white  an<l  yellou 

Zoiia  |M'llii<-i<l:i 
/oiio  of  Ziiiii,  <_>:;. 


LIBRARY 

COLLEGE    OP   DENTISTRY 
UNIVERSITY   OP  CALIFORNIA 


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